UBC Theses and Dissertations

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UBC Theses and Dissertations

Space weather and the MOST microsatellite Skaret, Kristina A. 2001

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S P A C E W E A T H E R A N D T H E M O S T M I C R O S A T E L L I T E b y K R I S H N A A . S K A R E T B . S c . , M c G i l l U n i v e r s i t y , 1 9 9 8 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L M E N T O F T H E R E Q U I R E M E N T S F O R T H E D E G R E E O F M A S T E R O F S C I E N C E i n T H E F A C U L T Y O F G R A D U A T E S T U D I E S D e p a r t m e n t o f P h y s i c s a n d A s t r o n o m y W e a c c e p t t h i s t h e s i s as c o n f o r m i n g to the r e q u i r e d s t a n d a r d T H E U N I V E R S I T Y O F B R I T I S H C O L U M B I A A p r i l , 2 0 0 1 © K r i s h n a S k a r e t , 2 0 0 1 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r a n a d v a n c e d d e g r e e at the U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e that t h e L i b r a r y s h a l l m a k e it f r e e l y a v a i l a b l e f o r r e f e r e n c e a n d s t u d y . I f u r t h e r a g r e e that p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s m a y b e g r a n t e d b y t h e h e a d o f m y d e p a r t m e n t o r b y h i s o r h e r r e p r e s e n t a t i v e s . It is u n d e r s t o o d that c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t b e a l l o w e d w i t h o u t m y w r i t t e n p e r m i s s i o n . D e p a r t m e n t o f P h y s i c s a n d A s t r o n o m y T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a V a n c o u v e r , C a n a d a II Abstract The MOST (Mcrovariability and Oscillations of Stars) microsatellite is designed to obtain the most precise stellar photometry (AL/L -10"6) ever achieved. In preparation for the launch of the first satellite devoted to asteroseismology, a complete evaluation of space weather in the baseline orbit including radiation analysis is performed, providing a 'weather forecast' for the mission in order to assist the MOST instrument team with crucial planning decisions. Results of assessing the effects of space weather include recommendations for the choice of orbit, design structure, operating guidelines, and data reduction guidelines. This analysis has aided the MOST team to convince the Canadian Space Agency (CSA) to identify a launch vehicle capable of taking MOST to a polar sun-synchronous orbit. Preliminary shielding recommendations have been incorporated into the mechanical design of the telescope. Estimates of the amount of degradation the C C D will experience, including the number of Single Event Effects (SEEs, effects caused by interaction with a single cosmic ray), have influenced current operating procedure guidelines. It is shown that radiation doses to the C C D are not expected to cause critical failure of the detector. A minimum mission lifetime is established for a worse-case radiation environment and found to be of sufficiently long duration to meet all primary scientific objectives. As the impact of the radiation environment (and other orbital environment related factors) is less than critical thresholds, the forecast for the MOST microsatellite looks 'sunny and warm'. • * • Mi Table of Contents A b s t r a c t i i T a b l e o f C o n t e n t s $ h L i s t o f T a b l e s VI L i s t o f F i g u r e s ' V I I L i s t o f A c r o n y m s \X A c k n o w l e d g m e n t s a n d D e d i c a t i o n X ( C h a p t e r 1: I n t r o d u c t i o n 1 1.1 S p a c e W e a t h e r a n d A s t r o n o m y 1 1.2 S p a c e W e a t h e r a n d M O S T 3 1.3 T h e M O S T m i c r o s a t e l l i t e : A S p a c e S e i s m o l o g y P i o n e e r 4 1.4 C h a r g e - C o u p l e d D e v i c e s ( C C D s ) 8 1.4.1 T h e M O S T C C D 11 C h a p t e r 2: S p a c e W e a t h e r 14 2.1 H i s t o r y 14 2 .2 C h a r g e d P a r t i c l e M o t i o n i n a M a g n e t i c F i e l d 15 2. 2.1 A d i a b a t i c I n v a r i a n t s 17 2 .2 .2 B a n d L C o - o r d i n a t e s 2 0 2 .3 T h e G e o m a g n e t o s p h e r e 2 1 2 .3 .1 T h e S o u t h A t l a n t i c A n o m a l y 2 3 2 .3 .2 G e o m a g n e t o s p h e r i c S h i e l d i n g 2 4 2 .3 .3 G e o m a g n e t i c S t o r m s 2 5 2.4 C h a r g e d P a r t i c l e P o p u l a t i o n s 2 6 2 .4 .1 M a g n e t o s p h e r i c P a r t i c l e s 2 7 2 .4 .2 S o l a r E n e r g e t i c P a r t i c l e s 3 0 2 .4 .3 G a l a c t i c C o s m i c R a d i a t i o n 31 2 .4 .4 T h e A n o m a l o u s C o m p o n e n t o f G a l a c t i c C o s m i c R a d i a t i o n 3 2 2.5 S o l a r C y c l e M o d u l a t i o n 33 C h a p t e r 3: M o d e l i n g t h e R a d i a t i o n E n v i r o n m e n t 3 7 3.1 A p p r o a c h 3 7 3 .2 A P 8 / A E 8 T r a p p e d P a r t i c l e M o d e l s 3 9 3:3 G e o m a g n e t i c S h i e l d i n g m o d e l s 4 0 3 .4 C R E M E 4 0 3.5 S o l a r E n e r g e t i c P a r t i c l e s 4 1 3 .6 U n c e r t a i n t i e s 4 3 IV C h a p t e r 4: C h o o s i n g a B a s e l i n e O r b i t 4 5 4 .1 T h e M O S T B a s e l i n e O r b i t 4 5 4 .2 C o s m i c R a y H i t s 4 6 4 .3 T h e C o n t i n u o u s V i e w i n g Z o n e 4 7 4 .4 T h e M O S T D u t y C y c l e 5 0 4 .5 E c l i p s e S e a s o n 53 4 .6 S t r a y L i g h t E f f e c t s 55 C h a p t e r 5: T h e W e a t h e r F o r e c a s t f o r the M O S T M i c r o s a t e l l i t e 5 9 5.1 T h e G e o m a g n e t i c F i e l d 5 9 5.2 G e o m a g n e t i c S h i e l d i n g .62 5.3 T r a p p e d P r o t o n s a n d E l e c t r o n s 63 5 .4 G a l a c t i c C o s m i c R a d i a t i o n 6 4 5.5 A n o m a l o u s C o s m i c R a d i a t i o n 6 7 5 .6 S o l a r E n e r g e t i c P a r t i c l e s 6 8 5 .7 S a t e l l i t e S h i e l d i n g 7 0 5.8 C u m u l a t i v e D o s e s 7 6 5 .9 A l t i t u d e v e r s u s D o s e 7 7 C h a p t e r 6: R a i n o r S h i n e ? I m p l i c a t i o n s o f S p a c e W e a t h e r o n M O S T 7 9 6.1 C C D D a m a g e 80 6 .1 .1 D a r k C u r r e n t 82 6 .1 .2 D a m a g e d P i x e l s 84 6 .1 .3 R T S • 85 6 .1 .4 F l a t B a n d V o l t a g e S h i f t s 86 6 .1 .5 C T E D e g r a d a t i o n 8 7 6 .1 .6 I m p l i c a t i o n s f o r the P h o t o m e t r i c E r r o r B u d g e t 8 9 6.2 S i n g l e E v e n t E f f e c t s ( S E E s ) 8 9 C h a p t e r 7: M i t i g a t i o n o f E n v i r o n m e n t a l D a m a g e 9 6 7.1 R e c o m m e n d a t i o n s f o r the M O S T M i c r o s a t e l l i t e . 96 7.2 O t h e r A s t e r o s e i s m o l o g y M i s s i o n s 9 7 7.3 F u t u r e W o r k 9 8 R e f e r e n c e s : . . 100 A p p e n d i x A : M O S T T a r g e t S tars 104 A p p e n d i x B : O r b i t a l P a r a m e t e r s 105 A p p e n d i x C : T a r g e t S t a r D w e l l T i m e i n t h e C V Z 109 A p p e n d i x D : M a p s o f T r a p p e d P r o t o n a n d E l e c t r o n F l u x 113 A p p e n d i x E : C u m u l a t i v e D o s e s A p p e n d i x F : S p e c i f i c a t i o n s S h e e t f o r M a r c o n i C C D 4 6 - 2 0 List of Tables: T a b l e 1.1 N o i s e l e v e l a n d d e t e c t i o n l i m i t s o f t h e M O S T m i c r o s a t e l l i t e 11 T a b l e 1.2 C C D 4 7 - 2 0 D e s c r i p t i o n 11 T a b l e 2.1 L o c a t i o n o f c e n t r o i d o f m i n i m u m o f S A A b e t w e e n 1 9 7 0 a n d 1993 2 3 T a b l e 2 .2 C o m p a r i s o n o f t r a p p e d p a r t i c l e p o p u l a t i o n s 2 7 T a b l e 5.1 U n c e r t a i n t i e s i n r a d i a t i o n e n v i r o n m e n t m o d e l s 7 6 V VII List of Figures: F i g u r e 1.1 P h o t o o f a m o c k - u p o f the M O S T m i c r o s a t e l l i t e 4 F i g u r e 1.2 F a b r y m i c r o l e n s p u p i l i m a g e f r o m t e s t i n g o f t h e M O S T m i c r o l e n s a r r a y .6 F i g u r e 1.3 S c h e m a t i c o f t h e M O S T f o c a l p l a n e .7 F i g u r e 1.4 S c h e m a t i c o f C C D f u n c t i o n 9 F i g u r e 1.5 T o p v i e w o f C C D , s h o w i n g t h r e e gates 10 F i g u r e 1.6 S c h e m a t i c o f t y p i c a l b u r i e d c h a n n e l C C D , i n i n v e r t e d m o d e . . . 12 F i g u r e 2.1 M e r i d i a n p r o j e c t i o n o f a t r a p p e d c h a r g e d p a r t i c l e 14 F i g u r e 2 .2 A r t i s t s c o n c e p t i o n o f the V a n A l l e n r a d i a t i o n b e l t s 15 F i g u r e 2 .3 S c h e m a t i c o f c h a r g e d p a r t i c l e m o t i o n i n the g e o m a g n e t i c f i e l d 17 F i g u r e 2 .4 S c h e m a t i c o f t h e E a r t h ' s g e o m a g n e t o s p h e r e 21 F i g u r e 2.5 C r o s s s e c t i o n o f t h e r a d i a t i o n b e l t s s h o w i n g S A A 2 3 F i g u r e 2 .6 R a d i a l d i f f u s i o n i n r e s p o n s e t o a c o m p r e s s e d m a g n e t i c f i e l d 2 9 F i g u r e 2 . 7 S u n s p o t n u m b e r as a f u n c t i o n o f date 3 4 F i g u r e 2 .8 R e c e n t s u n s p o t d a t a s h o w i n g s o l a r a c t i v i t y c y c l e f o r t h e n e x t d e c a d e . 3 6 F i g u r e 3.1 A p p r o a c h to m o d e l i n g r a d i a t i o n e n v i r o n m e n t f o r the M O S T m i c r o s a t e l l i t e . . . 3 8 F i g u r e 4.1 D a t a f r o m t h e F U S E g u i d e c a m e r a c o m p a r i n g r e g i o n s i n a n d o u t o f S A A 4 6 F i g u r e 4 .2 S c h e m a t i c o f t h e M O S T b a s e l i n e o r b i t 4 7 F i g u r e 4 .3 M O S T targets a n d l i m i t s o f C V A p r o j e c t e d o n the s k y 4 9 F i g u r e 4 . 4 T h e s p e c t r a l w i n d o w f o r t h e M O S T m i c r o s a t e l l i t e 5 2 F i g u r e 4 .5 E c l i p s e d u r a t i o n f o r the M O S T b a s e l i n e o r b i t 5 4 F i g u r e 4 .6 L i g h t c u r v e t a k e n b y the s t a r - s e n s o r o n b o a r d the W I R E sa te l l i te 55 F i g u r e 4 . 7 S c h e m a t i c o f the M O S T o r b i t i n g t h e E a r t h l o o k i n g d o w n o n N o r t h P o l e 5 6 v i i i F i g u r e 4 .8 T h e t a as a f u n c t i o n o f L T A N o v e r the c o u r s e o f a y e a r 5 7 F i g u r e 4 . 9 M a x i m u m a l l o w a b l e v a l u e s o f L T A N f o r h e l i o s y n c h r o n o u s o r b i t s 5 8 F i g u r e 5.1 M a g n e t i c f i e l d s t r e n g t h f o r M O S T b a s e l i n e o r b i t 5 9 F i g u r e 5 .2 T r a p p e d p r o t o n s p e c t r a w i t h t h r e e d i f f e r e n t m a g n e t i c f i e l d m o d e l s 61 F i g u r e 5.3 G e o m a g n e t i c t r a n s m i s s i o n f u n c t i o n f o r t h e M O S T b a s e l i n e o r b i t 6 2 F i g u r e 5 .4 P r o t o n a n d e l e c t r o n f l u e n c e o v e r M O S T m i n i m u m m i s s i o n l i f e t i m e 6 3 F i g u r e 5 .5 I n t e g r a l f l u x e n e r g y s p e c t r u m o f G C R 65 F i g u r e 5 .6 D i f f e r e n t i a l f l u x e n e r g y s p e c t r u m o f G C R 6 6 F i g u r e 5 .7 I n t e g r a l a n d d i f f e r e n t i a l f l u x e n e r g y s p e c t r a o f A C R 6 8 F i g u r e 5.8 D i f f e r e n t i a l e n e r g y s p e c t r a o f S E P e v e n t s 6 9 F i g u r e 5 .9 D o s e v s . D e p t h c u r v e f o r s i m p l e s h i e l d i n g g e o m e t r y 71 F i g u r e 5 .10 E n g i n e e r i n g s c h e m a t i c o f t h e p r e l i m i n a r y M O S T sa te l l i te d e s i g n 7 2 F i g u r e 5 .11 C o m p a r i s o n o f the p r o t o n f l u e n c e w i t h a n d w i t h o u t s h i e l d i n g 73 F i g u r e 5 .12 L E T s p e c t r a o f t r a p p e d p r o t o n s w i t h d i f f e r e n t s h i e l d i n g 7 4 F i g u r e 5 .13 L E T s p e c t r a o f s o l a r e n e r g e t i c p r o t o n s as m o d e l e d b y J P L 9 1 7 5 F i g u r e 5 .14 L E T s p e c t r a d u e to G C R 7 5 F i g u r e 5 .15 D o s e at t h e c e n t e r o f a n A l s p h e r e w i t h v a r y i n g a l t i t u d e o r b i t s 7 7 F i g u r e 5 . 1 6 A p p r o x i m a t e b o u n d a r y o f t h e S A A at 6 0 0 , 8 0 0 , a n d 1 0 0 0 k m a l t i t u d e 7 8 F i g u r e 6.1 C h a r g e g e n e r a t i o n o r i o n i s a t i o n d a m a g e o c c u r i n a C C D 80 F i g u r e 6 .2 D i s p l a c e m e n t d a m a g e 81 F i g u r e 6.3 N o n - i o n i s i n g e n e r g y l o s s as a f u n c t i o n o f A l s h i e l d i n g t h i c k n e s s 8 8 F i g u r e 6 .4 P r o t o n i n d u c e d s i n g l e e v e n t e f f e c t rate 9 2 F i g u r e 6.5 H e a v y i o n i n d u c e d u p s e t s v s . s e n s i t i v e v o l u m e a n d c r i t i c a l c h a r g e 9 4 ix F i g u r e 7.1 I o n i s i n g d o s e s f o r M O S T , M O N S a n d C O R O T 9 7 F i g u r e A . 1 P o s i t i o n a l p l o t o f t r a p p e d p r o t o n f l u x >1 .0 M e V 113 F i g u r e A . 2 P o s i t i o n a l p l o t o f t r a p p e d p r o t o n f l u x > 1 0 . 0 M e V 114 F i g u r e A . 3 P o s i t i o n a l p l o t o f t r a p p e d p r o t o n f l u x > 3 0 0 . 0 M e V 114 F i g u r e A . 4 P o s i t i o n a l p l o t o f t r a p p e d e l e c t r o n f l u x >1 .0 M e V 115 F i g u r e A . 5 P o s i t i o n a l p l o t o f t r a p p e d e l e c t r o n f l u x >5 .0 M e V 115 LIST OF ACRONYMS A C R : A n o m a l o u s C o s m i c R a y s A C S : A t t i t u d e C o n t r o l S y s t e m C C D : C h a r g e - C o u p l e d D e v i c e C M E : C o r o n a l M a s s E j e c t i o n C R A N D : C o s m i c R a y A l b e d o N e u t r o n D e c a y C R E M E : C o s m i c R a y E f f e c t s o n M i c r o - E l e c t r o n i c s C R R E S : C o m b i n e d R e l e a s e a n d R a d i a t i o n E f f e c t s S a t e l l i t e C V Z : C o n t i n u o u s V i e w i n g Z o n e D A O : D o m i n i o n A s t r o p h y s i c a l O b s e r v a t o r y D S N U : D a r k S i g n a l N o n - U n i f o r m i t y E S R T C : E u r o p e a n S p a c e R e s e a r c h a n d T e c h n o l o g y C e n t e r F U S E : F a r - i n f r a r e d U l t r a v i o l e t E x p l o r e r F E S : F i n e E r r o r S e n s o r G C R : G a l a c t i c C o s m i c R a d i a t i o n H S T : H u b b l e S p a c e T e l e s c o p e I G R F : I n t e r n a t i o n a l G e o m a g n e t i c R e f e r e n c e F i e l d E V I O : I n v e r t e d M o d e M I S : M e t a l I n s u l a t i n g S e m i c o n d u c t o r M O S : M e t a l O x i d e S e m i c o n d u c t o r M O S F E T : M e t a l O x i d e S e m i c o n d u c t o r F i e l d E f f e c t T r a n s i s t o r M O S T : M i c r o v a r i a b i l i t y a n d O s c i l l a t i o n s o f Stars L E O : L o w E a r t h O r b i t O N V : O r b i t N o r m a l V e c t o r Q E : Q u a n t u m E f f i c i e n c y S A A : S o u t h A t l a n t i c A n o m a l y S E B : S i n g l e E v e n t B u r n o u t S E E : S i n g l e E v e n t E f f e c t s S E F : S i n g l e E v e n t F a i l u r e S E F I : S i n g l e E v e n t F u n c t i o n a l I n t e r r u p t S E G R : S i n g l e E v e n t G a t e R u p t u r e S E L : S i n g l e E v e n t L a t c h u p S E P : S o l a r E n e r g e t i c P a r t i c l e S E U : S i n g l e E v e n t U p s e t s S H E : S i n g l e H a r d E r r o r S O H O : S o l a r a n d H e l i o s p h e r i c O b s e r v a t o r y S P E N V I S : S p a c e E n v i r o n m e n t I n f o r m a t i o n S y s t e m W E T : W h o l e E a r t h T e l e s c o p e W I R E : W i d e - f i e l d I n f r a - R e d E x p l o r e r XI Acknowledgements and Dedication M a n y p e o p l e h a v e c o n t r i b u t e d t o t h i s t h e s i s i n m a n y d i f f e r e n t w a y s . O n the a c a d e m i c s i d e , m y s i n c e r e t h a n k s g o o u t to m y s u p e r v i s o r , J a y m i e M a t t h e w s , f o r a l w a y s s t a y i n g i n t e r e s t e d a n d p a t i e n t , w i t h h i s s e n s e o f h u m o u r c o n s t a n t l y p r e v a i l i n g . I a m a l s o g r a t e f u l to the M O S T s c i e n c e t e a m at U B C , R a i n e r K u s c h n i g , G o r d o n W a l k e r , R o n J o h n s t o n , J o h n P a z d e r , a n d E v g e n y a S h k o l n i k f o r t h e i r c o m m e n t s a n d d i s c u s s i o n s , a n d f o r t h e i r s u p p o r t o f m y w o r k , a n d to o u r p a r t n e r s at C S A ( G l e n C a m p b e l l ) a n d D y n a c o n . I ' m g r a t e f u l to S t e p h e n s o n Y a n g f o r i n t r o d u c i n g m e to the w o r l d o f o b s e r v a t i o n a l a s t r o n o m y . A n d o f c o u r s e , I o w e m u c h to J a n e t J o h n s o n , o u r g r a d u a t e s e c r e t a r y at U B C f o r h e r e n d l e s s p a t i e n c e a n d great a d v i c e , as w e l l as to a l l m y f r i e n d s a n d f a m i l y w h o h e l p e d m e t h r o u g h h a r d t i m e s b y p r o v i d i n g g o o d t i m e s ( y o u k n o w w h o y o u a r e ! ) . T h i s t h e s i s is d e d i c a t e d to m y f a t h e r , D r . R e g J . S k a r e t ( 1 9 4 9 - 2 0 0 0 ) . H i s i n c r e d i b l e s u p p o r t , e n c o u r a g e m e n t , a n d e n t h u s i a s m e n s u r e d that I f o l l o w m y d r e a m s . I c o u l d n o t h a v e c o m p l e t e d th is p r o j e c t w i t h o u t h i s g u i d a n c e . H e w a s a n a m a z i n g m a n , a n d a n e v e n m o r e a m a z i n g fa ther . A s y o u r e a d t h i s t h e s i s , k n o w that I o w e m u c h o f e v e r y s u c c e s s i n m y l i f e t o h i m . H e w i l l b e t r u l y m i s s e d . L o o k d a d - 1 f i n i s h e d ! 1 Chapter 1: Introduction 1.1 Space Weather and Astronomy Astronomers who use space telescopes don't have to cope with the hassles of a cloudy night at the observatory, or poor seeing due to atmospheric interference. At first glance, the space environment would appear to be very calm and 'weather-free'. But on closer inspection, one finds that low-Earth orbit (LEO) is actually quite active, has its own weather, and its own set of problems which space astronomers must be aware of. The chance to peer out at space from outside the atmosphere affords astronomers the ability to analyse wavelength regions opaque through the Earth's atmosphere. For others, the telescope needs to be in orbit about the Earth to escape the scintillation noise associated with a turbulent atmosphere and to have a complete duty cycle. The sensitivity and capacity of micro-electronics such as memory devices, signal processors, and photo-electric detectors has provided astronomers with a new chance to probe regimes not before open for observation. However, the trade-off has repetitively been an increasing sensitivity to the charged particle environment associated with the space environment. The near-Earth radiation environment is complex. A l l variety of atoms, from light protons to uranium nuclei (z=92), are accelerated to high energies by a wide variety of sources, some of which remain mysteries even today. Plasma from the solar wind constantly injects and replenishes the supply of charged particles which bombard satellites. Hence, the number and intensity of the particles varies strongly during the solar cycle. The presence of'cosmic radiation' first discovered in 1912 by Hess (Van Allen 1983) creates adverse conditions in the space orbital environment. During very strong Coronal Mass Ejections (CMEs) from the sun, charged particle interaction with the Earth's magnetosphere can be so severe that charged particles reach northern latitudes, disrupting power supplies, creating dangerous currents through long oil pipelines, and wiping out radio communications. These events are few and isolated to solar maximum here on Earth. However, in the orbital environment with less geomagnetic shielding, satellites experience much higher doses as well as a greater duration of exposure to 2 c h a r g e d p a r t i c l e s . T h u s , sa te l l i tes i n L E O m u s t b e d e s i g n e d t o t o l e r a t e i s o l a t e d s o l a r e v e n t s a s s o c i a t e d w i t h a l a r g e flux o f c h a r g e d p a r t i c l e s as w e l l as the a m b i e n t flux o f c h a r g e d p a r t i c l e s m o s t l y c o n c e n t r a t e d i n t h e V a n A l l e n R a d i a t i o n b e l t s . T h e r a d i a t i o n e n v i r o n m e n t c a n p r o d u c e a m y r i a d o f h a z a r d s to a n o r b i t i n g s p a c e c r a f t . T h e m o s t c r i t i c a l e f f e c t i s a S i n g l e E v e n t F a i l u r e ( S E F ) i n w h i c h a s i n g l e i n t e r a c t i o n b e t w e e n a c h a r g e d p a r t i c l e a n d a n o n b o a r d m i c r o - e l e c t r o n i c ( u s u a l l y m e m o r y ) d e v i c e c a u s e s c r i t i c a l f a i l u r e . L u c k i l y , S E F s are v e r y r a r e i n m o d e r n sa te l l i tes as c r i t i c a l m i c r o e l e c t r o n i c s a r e n o r m a l l y d u p l i c a t e d to p r o v i d e o n b o a r d r e d u n d a n c y , o r b a c k u p . S E F s a r e j u s t o n e o f a c l a s s o f e f f e c t s c a l l e d S i n g l e E v e n t E f f e c t s ( S E E s ; S e c t i o n 6 .2) w h i c h are c a u s e d b y a s i n g l e p a r t i c l e i n t e r a c t i o n w i t h a m i c r o - e l e c t r o n i c d e v i c e . M o s t S E E s d o n o t i n t e r r u p t n o r m a l o p e r a t i o n s b u t d o n e c e s s i t a t e r e g u l a r g r o u n d c o m m u n i c a t i o n s w i t h t h e sate l l i te i n c l u d i n g r e g u l a r u p l i n k o f o p e r a t i n g s e q u e n c e s to a v o i d m o r e c r i t i c a l e f f e c t s . T h e p r e s e n c e o f the V a n A l l e n R a d i a t i o n b e l t s a n d the i m p l i c a t i o n s o f r e g u l a r t r a v e r s e s t h r o u g h t h e i r p a r t i c l e r i c h e n v i r o n m e n t s o f t e n i n f l u e n c e s t h e c h o i c e o f o r b i t f o r a sa te l l i te ( C h a p t e r 4) . I n t h e h e a r t o f t h e r a d i a t i o n b e l t s i n L E O ( a f e a t u r e c a l l e d the S o u t h A t l a n t i c A n o m a l y ( S A A ) b e c a u s e o f its g e o g r a p h i c a l l o c a t i o n ) it i s o f t e n n o t p o s s i b l e to c o l l e c t g o o d d a t a . C h a r g e d p a r t i c l e s m a y h i t d e t e c t o r s c r e a t i n g s p u r i o u s s i g n a l ( S e c t i o n 4 .2 ) , o r as i n the c a s e o f the H u b b l e S p a c e T e l e s c o p e ( H S T ) , t h e sa te l l i te m a y b e p o w e r e d d o w n i n o r d e r to r e d u c e l o n g t e r m d a m a g e . F o r s p a c e a s t e r o s e i s m o l o g y m i s s i o n s s u c h as M O S T ( S e c t i o n 1.3), o n e g r e a t a d v a n t a g e o f b e i n g i n o r b i t i s t h e a b i l i t y t o o b s e r v e a ta rget f o r a n e x t e n d e d p e r i o d o f t i m e . T h u s , the l o s s o f d a t a t h r o u g h the S A A c a n b e d e t r i m e n t a l to m e e t i n g s c i e n c e g o a l s . R e g u l a r p a s s e s t h r o u g h t h e r a d i a t i o n b e l t s a l s o c a u s e c u m u l a t i v e d a m a g e i n s e n s i t i v e m i c r o e l e c t r o n i c s . G r a d u a l l y , c h a r g e d p a r t i c l e s c a n d e s t r o y t h e p h y s i c a l p r o p e r t i e s o f s p e c i f i c d e v i c e s . I n p a r t i c u l a r , s i l i c o n la t t i ces are b r o k e n d o w n b y c h a r g e d p a r t i c l e s . C h a r g e c o u p l e d d e v i c e s ( C C D s ; S e c t i o n 1.4) a r e o n e t y p e o f d e v i c e u t i l i s e d r e g u l a r l y b y a s t r o n o m e r s a n d s p a c e a s t r o n o m e r s a l i k e a n d are s u s c e p t i b l e to t h i s e f f e c t o f s p a c e w e a t h e r . C h a r g e m a y a l s o a c c u m u l a t e w i t h i n c i r c u i t s o v e r t i m e . I f t h e c u m u l a t i v e c h a r g e b u i l d u p is s u f f i c i e n t l y h i g h to c r e a t e a d i s c h a r g e , c r i t i c a l f a i l u r e i s a p o s s i b i l i t y d e p e n d i n g o n t h e d e s i g n o f the sate l l i te . 3 S p a c e a s t r o n o m e r s m u s t a l s o b e a w a r e o f h o w the o r b i t a l e n v i r o n m e n t e f f e c t s par t s s p e c i f i c to t e l e s c o p e s . C o a t i n g s u s e d o n o p t i c a l c o m p o n e n t s c o u l d p o t e n t i a l l y i n t e r a c t w i t h a t o m i c o x y g e n to c a u s e b r o w n i n g . I n o r d e r to m i t i g a t e the d a m a g e c a u s e d b y s p a c e w e a t h e r a n d a v o i d c r i t i c a l f a i l u r e s , it i s e s s e n t i a l f o r a t h o r o u g h r a d i a t i o n a n a l y s i s to b e p e r f o r m e d o n a s p a c e c r a f t . A sa te l l i te s h o u l d a l w a y s u s e r a d i a t i o n h a r d e n e d par ts , o n - b o a r d r e d u n d a n c y i n c r i t i c a l o p e r a t i n g d e v i c e s , a n d r e g u l a r p l a n n e d g r o u n d c o m m u n i c a t i o n s . I n c o r p o r a t i o n o f a s p a c e ' w e a t h e r f o r e c a s t ' i n t o o p e r a t i n g p r o c e d u r e a n d d a t a r e d u c t i o n g u i d e l i n e s w i l l h e l p e n s u r e a l l s c i e n t i f i c g o a l s w i l l b e m e t . A g o o d k n o w l e d g e o f t h e a m b i e n t r a d i a t i o n e n v i r o n m e n t o f t h e sa te l l i te s h o u l d a l s o p r o v i d e a m i n i m u m m i s s i o n l i f e t i m e e s t i m a t e a n d b e u s e d i n d e s i g n i n g t h e sa te l l i te to m a k e s u r e t h e r e i s s u f f i c i e n t o n - b o a r d s h i e l d i n g . 1.2 Space Weather and MOST T h e a i m o f t h i s t h e s i s i s to p r o v i d e a c o m p l e t e r a d i a t i o n a n a l y s i s f o r t h e M O S T ( M c r o v a r i a b i l i t y a n d O s c i l l a t i o n s o f S tars ) m i c r o s a t e l l i t e i n o r d e r to ass is t the M O S T i n s t r u m e n t t e a m w i t h c r u c i a l p l a n n i n g d e c i s i o n s , e s s e n t i a l l y p r o v i d i n g t h e ' w e a t h e r f o r e c a s t ' f o r t h e m i s s i o n . A b r i e f i n t r o d u c t i o n to t h e M O S T m i s s i o n a n d the M O S T C C D is f o u n d i n S e c t i o n s 1.3 a n d 1.4 r e s p e c t i v e l y . C h a p t e r 2 i s a p r i m e r o n t h e p h y s i c a l p r o c e s s e s that t r a p p a r t i c l e s i n the E a r t h ' s m a g n e t o s p h e r e . C h a p t e r 3 d e s c r i b e s the a p p r o a c h t o m o d e l i n g t h e r a d i a t i o n e n v i r o n m e n t e m p l o y e d i n t h i s s t u d y . I n C h a p t e r 4 , t h e b a s e l i n e o r b i t a l p a r a m e t e r s a r e e v a l u a t e d f o r the M O S T m i c r o s a t e l l i t e m i s s i o n . T h i s a n a l y s i s h a s a i d e d t h e M O S T t e a m to c o n v i n c e the C a n a d i a n S p a c e A g e n c y ( C S A ) to i d e n t i f y a l a u n c h v e h i c l e c a p a b l e o f t a k i n g M O S T t o a p o l a r s u n -s y n c h r o n o u s o r b i t . D e v i a t i o n s i n L o c a l T i m e o f A s c e n d i n g N o d e ( L T A N ) w e r e s h o w n t o a d v e r s e l y a f f e c t s c i e n c e o p e r a t i o n s a n d h e n c e , l a u n c h o p p o r t u n i t i e s to t h e s e o r b i t s w e r e r u l e d out . C h a p t e r 5 e m p l o y s t h e t e c h n i q u e s o u t l i n e d i n C h a p t e r 3 to assess t h e r a d i a t i o n e n v i r o n m e n t f o r the b a s e l i n e o r b i t . T h e r a d i a t i o n e n v i r o n m e n t o f the b a s e l i n e o r b i t w a s u s e d to p r o v i d e a f o r e c a s t f o r M O S T . 4 T h i s w e a t h e r f o r e c a s t h a s p l a y e d i m p o r t a n t r o l e i n t h e d e v e l o p m e n t o f t h e M O S T m i c r o s a t e l l i t e m i s s i o n . A s t h i s w o r k w a s p r o g r e s s i n g , s o w a s t h e m e c h a n i c a l d e s i g n o f the t e l e s c o p e . B a s e d o n r e s u l t s p r e s e n t e d h e r e , the d e s i g n w a s fine-tuned s u c h that s u f f i c i e n t s h i e l d i n g i s p r e s e n t to p r o t e c t s e n s i t i v e s p a c e c r a f t par ts , y e t m i n i m u m a m o u n t s o f h e a v y m a t e r i a l s are u s e d i n o r d e r to r e d u c e m a s s c o n s t r a i n t s . C u r r e n t o p e r a t i n g p r o c e d u r e g u i d e l i n e s w e r e e s t a b l i s h e d i n c o n j u n c t i o n w i t h t h i s s t u d y i n o r d e r to m i n i m i s e i m p a c t o n s c i e n t i f i c d a t a d u e to c o s m i c r a y s ( S e c t i o n 4 .2 ) a n d s i n g l e e v e n t e f f e c t s ( S E E s , S e c t i o n 6.2) . A m i n i m u m m i s s i o n l i f e t i m e w a s e s t a b l i s h e d f o r a w o r s e - c a s e r a d i a t i o n e n v i r o n m e n t a n d f o u n d t o b e o f s u f f i c i e n t l y l o n g d u r a t i o n t o m e e t a l l p r i m a r y s c i e n t i f i c o b j e c t i v e s . A s the i m p a c t o f the r a d i a t i o n e n v i r o n m e n t ( a n d o t h e r o r b i t a l e n v i r o n m e n t r e l a t e d f a c t o r s ) i s l e s s t h a n c r i t i c a l t h r e s h o l d s , the f o r e c a s t f o r the M O S T m i c r o s a t e l l i t e l o o k s ' s u n n y a n d w a r m ' . 1.3 The MOST microsatellite: A Space Seismology Pioneer T h e M O S T s p a c e sa te l l i te p r o j e c t i s u n i q u e i n C a n a d i a n a s t r o n o m y . F u n d e d b y t h e C a n a d i a n S p a c e A g e n c y ( C S A ) , M O S T is C a n a d a ' s first m i c r o s a t e l l i t e m i s s i o n ( the b u s is r o u g h l y the d i m e n s i o n a n d m a s s o f a s u i t c a s e ) . A p i c t u r e o f t h e sa te l l i te i t s e l f is s h o w n i n F i g u r e 1.1. T h e d r i v i n g s c i e n c e g o a l b e h i n d M O S T i s to p r o b e t h e i n t e r n a l s t r u c t u r e a n d c e n t r a l c o m p o s i t i o n o f n e a r b y stars b y m e a s u r i n g b r i g h t n e s s o s c i l l a t i o n s w i t h a m p l i t u d e s as s m a l l as a f e w m i c r o -m a g n i t u d e s t o a p p l y t h e t e c h n i q u e s o f a s t e r o s e i s m o l o g y . A s t e r o s e i s m o l o g y w a s b o r n t h r o u g h h e l i o s e i s m o l o g y , t h e s t u d y o f t h e five-minute o s c i l l a t i o n s o f t h e s u n ( D e m a r q u e & G u e n t h e r 1999) . It h a s a l l o w e d a s t r o n o m e r s to p e e r i n t o the sun 's F i g u r e 1.1 Photo of a mock-up of the MOST microsatellite with coffee mug showing scale. i n t e r i o r a n d c o m p a r e r e s u l t s to the S t a n d a r d S o l a r M o d e l ( M a t t h e w s 1990) . S i m i l a r t o t h e w a y g e o p h y s i c i s t s u s e p r e s s u r e w a v e s ( p - w a v e s ) c r e a t e d b y 5 e a r t h q u a k e s t o i n f e r t h e t h i c k n e s s a n d c o m p o s i t i o n o f t h e E a r t h ' s i n t e r n a l l a y e r s , a s t e r o s e i s m o l o g i s t s u s e s o u n d w a v e s , i n d u c e d b y c o n v e c t i v e t u r b u l e n c e o f the S u n ' s s u r f a c e , to p r o b e t h e sun's i n t e r i o r . A s t e r o s e i s m o l o g i s t s u s e s p h e r i c a l h a r m o n i c s to d e s c r i b e the nonradial pulsations c r e a t e d b y s o u n d w a v e s as t h e y r e s o n a t e i n a c o u s t i c c a v i t i e s b e n e a t h t h e s o l a r s u r f a c e . A s t h e b e h a v i o r o f t h e s o u n d w a v e s i s d i r e c t l y r e l a t e d to t h e m e d i u m i n w h i c h t h e y t r a v e l , t h e m o d e p a t t e r n s i m p r i n t e d o n t h e s t e l l a r s u r f a c e b y t h e s e w a v e s c o n t a i n s i n f o r m a t i o n o n the i n t e r n a l s t r u c t u r e a n d c o m p o s i t i o n o f the star. T h u s , t h e t o o l s o f a n a s t e r o s e i s m o l o g i s t a r e the e i g e n f r e q u e n c i e s ( a n d t o a l e s s e r ex tent , a m p l i t u d e s ) o f the m o d e pat terns ( T a s s o u l 1990) . T h e d i f f e r e n c e b e t w e e n a s t e r o s e i s m o l o g y a n d h e l i o s e i s m o l o g y i s that o n l y s i m p l e n o n r a d i a l pa t terns ( i .e . l o w d e g r e e (/) a n d h i g h o v e r t o n e ( « ) ) a re d e t e c t a b l e w h e n o b s e r v i n g t h e i n t e g r a t e d l i g h t f r o m a p o i n t s o u r c e . T h e s u n is r e s o l v a b l e as a d i s k a n d t h u s , e v e n h i g h s p a t i a l f r e q u e n c y m o d e s w h i c h d o n o t r e s u l t i n v a r i a t i o n s o f t h e t o t a l d i s c are d e t e c t a b l e . T h e c h a l l e n g e i n the o b s e r v a t i o n o f s e i s m i c o s c i l l a t i o n s i s the r e l a t i v e l y l o w c h a n g e i n e i t h e r D o p p l e r v e l o c i t y o r o v e r a l l b r i g h t n e s s o f the star. T h e D o p p l e r v e l o c i t i e s d u e t o v i b r a t i o n o f the S u n i n i n t e g r a t e d l i g h t a r e o n l y a f e w c m / s , a n d the o v e r a l l b r i g h t n e s s f l u c t u a t i o n s are o n t h e o r d e r o f a f e w m i c r o m a g n i t u d e s . C u r r e n t g r o u n d - b a s e d d e t e c t i o n t h r e s h o l d s are ~ 3 m / s i n D o p p l e r v e l o c i t y a n d 100 m i c r o m a g n i t u d e s i n b r i g h t n e s s f l u c t u a t i o n s ( p h o t o m e t r i c p r e c i s i o n i s l i m i t e d b y n o i s e d u e to a t m o s p h e r i c s c i n t i l l a t i o n ) . R e c e n t r e p o r t s o f o s c i l l a t i o n s i n a l p h a U r s a e M a j o r i s b y B u s a z i et a l . ( 1 9 9 9 ) , u s i n g t h e s t a r s e n s o r c a m e r a o n b o a r d the f a i l e d i n f r a r e d sate l l i te W I R E , s h o w that it i s p o s s i b l e to de tec t l o w a m p l i t u d e s te l lar v a r i a b i l i t y f r o m s p a c e . H o w e v e r , t h e v a r i a t i o n s c o r r e s p o n d t o p e r i o d s o f d a y s a n d h o u r s , a n d a m p l i t u d e s o f h u n d r e d s o f m i c r o m a g n i t u d e s , w e l l a b o v e t h e r e g i m e to b e e x p l o r e d b y M O S T . T h e M O S T d e s i g n is o p t i m i z e d to de tec t o s c i l l a t i o n s o f a m p l i t u d e s o f a f e w m i c r o m a g i n as f e w as t e n d a y s o f m o n i t o r i n g a star b r i g h t e r t h a n V ~ 6 ( s o l a r p - m o d e s d e c a y i n - 1 0 d a y s ) . I n o r d e r t o d e t e c t s o l a r - t y p e o s c i l l a t i o n s o f 4 p p m a m p l i t u d e i n a V = 3 . 0 m a g n i t u d e star w i t h 9 9 % c o n f i d e n c e , the r m s n o i s e l e v e l m u s t b e b e l o w 1 . 0 8 % p p m , e q u i v a l e n t to a s i g n a l t o n o i s e ( S / N ) v a l u e o f 3 . 7 ( M a t t h e w s & K u s c h n i g 2 0 0 0 ) . T a b l e 1.1 s h o w s t h e d e t e c t i o n l i m i t s b a s e d o n n u m e r i c a l s i m u l a t i o n s p e r f o r m e d b y K u s c h n i g ( 2 0 0 0 ) . M a i n t a i n i n g a h i g h d u t y c y c l e w i l l r e d u c e r e l a t i v e b a c k g r o u n d n o i s e 6 Target Star Window TSYV Figure 1.2 Fabry microlens pupil image as projected on the C C D (after Matthews & Kuschnig, 2000b) c o n t r i b u t i o n s to a l l o w M O S T to r e s o l v e fine s t ruc ture i n the s t e l l a r e i g e n f r e q u e n c y s p e c t r u m , a p a r t i c u l a r l y s e n s i t i v e t o o l f o r m e a s u r i n g c o r e H e f r a c t i o n . T h u s , w e w i l l b e a b l e to date individual m a i n s e q u e n c e stars. A s t e r o s e i s m o l o g y o f m e t a l p o o r s u b d w a r f s , b e l i e v e d t o b e the o l d e s t o b j e c t s i n t h e g a l a x y d u e t o t h e i r p r i m i t i v e c o m p o s i t i o n , w i l l a l l o w u s t o p l a c e a m e a n i n g f u l l o w e r l i m i t o n the a g e o f t h e M i l k y W a y a n d t h e U n i v e r s e . T h e M O S T t e a m h a s a d o p t e d a s i m p l e d e s i g n f o r the s p a c e p h o t o m e t e r . A 1 5 - c m M a k s u t o v t e l e s c o p e f e e d s a C h a r g e C o u p l e d D e v i c e ( C C D ) c a m e r a w i t h a set o f F a b r y m i c r o l e n s e s p o s i t i o n e d a b o v e t h e d e t e c t o r f o c a l p l a n e . T h e s t a r b e a m i s d i r e c t e d o n t o o n e o f t h e s e l e n s e s , w h i c h p r o j e c t s a n i m a g e o f the t e l e s c o p e p u p i l o n t o t h e C C D , c o v e r i n g a b o u t 2 0 0 0 p i x e l s i n t o t a l . A s the s t a r b e a m m o v e s o v e r t h e l e n s d u e to the t r a c k i n g e r r o r s o f t h e a t t i tude c o n t r o l s y s t e m ( A C S ) , t h e p u p i l i m a g e r e m a i n s fixed o n t h e s a m e p i x e l s ( F i g u r e 1.2). T h i s m i n i m i s e s the M O S T i n s t r u m e n t a l s e n s i t i v i t y to i m a g e w a n d e r a n d C C D f l a t f i e l d v a r i a t i o n s . A s c h e m a t i c o f the F o c a l p l a n e w i t h s c i e n c e C C D a n d A t t i t u d e C o n t r o l S y s t e m ( A C S ) C C D is s h o w n i n F i g u r e 1.3. T h e m i c r o l e n s a r r a y i s o n l y p r o j e c t e d o n t o a s m a l l a r e a o f t h e s c i e n c e C C D . S i n c e m a n y o f t h e M O S T s c i e n c e targets 7 ( A p p e n d i x A ) are v e r y b r i g h t ( > V ~ 2 ) , t h e l i g h t m u s t b e s p r e a d o u t o v e r a s u f f i c i e n t l y l a r g e n u m b e r o f p i x e l s i n o r d e r to r e d u c e t h e a m o u n t o f s a t u r a t i o n i n a g i v e n e x p o s u r e . H o w e v e r , t h e l i g h t m u s t b e c o n c e n t r a t e d e n o u g h s o that w h e n o b s e r v i n g f a i n t e r targets ( V < 6 ) , t h e t e l e s c o p e s t i l l o p e r a t e s i n a h i g h s i g n a l r e g i m e . O n e p u p i l i m a g e s p a n s 8 0 x 80 p i x e l s . M o r e b a c k g r o u n d o n t h e M O S T m i s s i o n a n d its s p e c i f i c s c i e n c e g o a l s c a n b e f o u n d at the M O S T w e b s i t e : h t t p : / / w w w . a s t r o . u b c . c a / M O S T / Figure 1.3 Schematic of the MOST focal plane showing Science and ACS CCDs. The dotted line circles represent the optical axis of the telescope. The Fabry microlens array focuses a pupil image of the star onto the lower right hand corner of the science CCD. 8 1.4 Charge-Coupled Devices (CCDs) A l t h o u g h t h e y w e r e f i r s t d e v e l o p e d as m e m o r y d e v i c e s , C C D s h a v e r e p l a c e d p h o t o g r a p h i c f i l m i n v i r t u a l l y e v e r y o p t i c a l a n d n e a r i n f r a - r e d a s t r o n o m i c a l i m a g i n g c a m e r a , s i n c e t h e s i l i c o n la t t i ce that t h e y are m a d e o f i s n a t u r a l l y l i g h t s e n s i t i v e t h r o u g h t h e p h o t o e l e c t r i c e f f e c t . A s t r o n o m e r s c a n m a n i p u l a t e t h e d i g i t a l i m a g e s w h i c h are p r o d u c e d b y C C D s a n d s u b t r a c t o f f n o i s e s o u r c e s s u c h a s t h e b a c k g r o u n d f r o m t h e s k y . T h e f u n d a m e n t a l b u i l d i n g b l o c k o f a C C D is a m e t a l - i n s u l a t o r - s e m i c o n d u c t o r ( M I S ) c a p a c i t o r . T h e c a p a c i t o r c o l l e c t s a n d s tores c h a r g e p a c k e t s , a n d t h e n t r a n s f e r s t h e c h a r g e p a c k e t to a n o t h e r c a p a c i t o r i n s e r i e s w h e n t h e v o l t a g e g a t i n g t h e c h a r g e i s c h a n g e d . H e n c e , t h e C C D is d u b b e d a charge coupled d e v i c e . E a c h M I S c a p a c i t o r is a r r a n g e d i n a s t r i n g o r r o w c a l l e d a s e r i a l - s h i f t r e g i s t e r , d o w n w h i c h c h a r g e p a c k e t s shi f t . I n a 2 - D i m a g i n g C C D , t h e s e r i a l s h i f t r e g i s t e r s a r e a r r a n g e d r o w b y r o w to f o r m a 2 - D p l a t e o f c a p a c i t o r s , e a c h i n d i v i d u a l l y s e n s i t i v e t o l i g h t f a l l i n g o n it t h r o u g h the p h o t o e l e c t r i c e f f e c t . T h e i m a g e i s p r o j e c t e d o n t o t h i s 2 - D p l a t e , a n d e l e c t r o n s are g e n e r a t e d i n e a c h c a p a c i t o r i n p r o p o r t i o n to t h e i n t e n s i t y o f t h e l i g h t f a l l i n g o n it. T h e n t h e v o l t a g e - g a t e d c h a n n e l s a r e m a n i p u l a t e d s u c h that a s i n g l e c h a r g e p a c k e t f r o m e a c h s e r i a l s h i f t r e g i s t e r i s t r a n s f e r r e d d o w n the r o w to a p e r p e n d i c u l a r s e r i a l s h i f t r e g i s t e r ( F i g u r e 1.4). T h i s p e r p e n d i c u l a r s h i f t r e g i s t e r c o l l e c t s a n u m b e r o f c h a r g e p a c k e t s e q u a l t o t h e n u m b e r o f r o w s o f s e r i a l s h i f t r e g i s t e r s i n t h e 2 - D d e v i c e a n d t r a n s f e r s t h e m o n e b y o n e to a r e c o r d i n g d e v i c e o r o u t p u t a m p l i f i e r . O n c e t h e p e r p e n d i c u l a r s h i f t r e g i s t e r is ' e m p t y ' , t h e n e t c h a r g e p a c k e t i n e a c h o f t h e p a r a l l e l s h i f t r e g i s t e r s i s r e a d out . C h a r g e s are g e n e r a t e d t h r o u g h t h e p h o t o e l e c t r i c e f f e c t , b u t m u s t b e s t o r e d b e f o r e t h e y a r e c o l l e c t e d . I n the s t a n d a r d o p e r a t i o n o f a C C D , a p o s i t i v e v o l t a g e i s a p p l i e d a c r o s s t h e ga te o f the M I S c a p a c i t o r , l ess t h a n t h e F e r m i p o t e n t i a l ( t h r e s h o l d p o t e n t i a l a b o v e w h i c h e l e c t r o n s c a n start m o v i n g ) n e e d e d to attract a s u b s t a n t i a l n u m b e r o f e l e c t r o n s . E l e c t r o n - h o l e p a i r s are g e n e r a t e d a n d p u s h e d a w a y b y the b u i l d u p o f c u r r e n t i n t h e c a p a c i t o r , t o w a r d s the e d g e s o f the c a p a c i t o r o r c o l u m n i s o l a t i o n r e g i o n s . T h i s l e a v e s a r e g i o n d e v o i d o f e l e c t r o n - h o l e p a i r s , o r a r e g i o n o f depletion. A s e l e c t r o n s are g e n e r a t e d t h e y c o l l e c t i n the d e p l e t i o n r e g i o n . T o t r a p e l e c t r o n s i n the c e n t e r o f the 9 C h a r g e p a c k e t s are r e a d o u t to a n o u t p u t a m p l i f i e r . Figure 1.4 Schematic of CCD function. Buckets of water are representative of capacitors collecting charge. The perpendicular serial shift register is responsible for reading out the rest of the 2D array to the output amplifier in order to record the image. (After Hardy, 1997) c a p a c i t o r , o r p i x e l , t h e c a p a c i t o r h a s t h r e e p o l y s i l i c o n gates , o r e l e c t r o d e s s u p p l y i n g v o l t a g e t h r o u g h the c a p a c i t o r , as i l l u s t r a t e d b y F i g u r e 1.5. T h e m i d d l e e l e c t r o d e is b i a s e d s u c h that the p o t e n t i a l w e l l c r e a t e d u n d e r n e a t h t h e s u r f a c e has a m i n i m u m i n t h e c e n t r a l r e g i o n o f t h e p i x e l , w h e r e the e l e c t r o n s ga ther . C h a n n e l s t o p s o n t h e s i d e s o f t h e p i x e l a n d t h e c o l l e c t i o n o f e l e c t r o n h o l e p a i r s at t h e p e r i m e t e r o f the C C D f u r t h e r ac ts as b a r r i e r s , t r a p p i n g the e l e c t r o n s i n the c e n t e r o f t h e p i x e l . F o r a m o r e d e t a i l e d h i s t o r y a n d d e s c r i p t i o n o f C C D s , see H a r d y ( 1 9 9 7 ) . 10 T h e p r e c i s i o n o f C C D s m a k e s t h e m a n i d e a l d e t e c t o r f o r t h e M O S T m i c r o s a t e l l i t e . T e s t s i n d e m o n s t r a t i o n o f the f u n c t i o n a l i t y o f t h e K e p l e r m i s s i o n b y J e n k i n s et a l . ( 1 9 9 6 ) s h o w e d that a b a c k - i l l u m i n a t e d R e t i c o n C C D w a s c a p a b l e o f d e t e c t i n g p l a n e t a r y t r a n s i t s , a s i g n a l that is o n l y a b o u t 8 0 p p m o f t h e target stars b r i g h t n e s s ( o n c e c a l i b r a t e d f o r the e f f e c t s o f m o t i o n ) . I n f a c t , t h e tests s h o w e d that t h e C C D w a s s h o t n o i s e l i m i t e d a n d c a p a b l e o f d e t e c t i n g a s i g n a l at a l e v e l o f 3 p p m . T h e M O S T C C D is m a n u f a c t u r e d b y M a r c o n i , a n d is s l i g h t l y d i f f e r e n t f r o m t h e R e t i c o n C C D i n d i m e n s i o n a n d s e n s i t i v i t y . H o w e v e r , n u m e r i c a l s i m u l a t i o n s o f t h e M O S T p h o t o m e t e r b y K u s c h n i g s h o w that s t e l l a r o s c i l l a t i o n s i g n a l s w i l l b e d e t e c t e d ( M a t t h e w s & K u s c h n i g 2 0 0 0 a ) . I n o b s e r v a t i o n s o f a 4 t h m a g n i t u d e star, the n o i s e l e v e l o f ~ 1 p p m w i l l b e d o m i n a n t l y d u e t o p h o t o n s h o t n o i s e (>70%) , a r e d u c e d d u t y c y c l e (>7%, S e c t i o n 4.3), a n d s t e l l a r g r a n u l a t i o n n o i s e ( - 5 % ) . A s o l a r o s c i l l a t i o n s p e c t r u m w i l l b e d e t e c t e d w i t h 9 9 % c o n f i d e n c e at 4.1 p p m . T a b l e 1 s h o w s the resul ts o f t h e n u m e r i c a l s i m u l a t i o n s f o r stars o f v a r y i n g m a g n i t u d e . Pixel outline Gates Channel Stop Figure 1.5 Top view of CCD pixel, showing three gates 11 T a r g e t star e x p o s u r e d a t a rate n o i s e l e v e l s i g n a l d e t e c t i o n l i m i t t i m e b a s e m a g n i t u d e ( V ) t i m e (s) # / m i n ( p p m ) ( p p m ) ( 9 9 % ) ( d a y s ) 0 .4 1 10 0 .72 2 .6 10 1.2 2 10 0 .72 2 .6 10 3 12 5 1.02 3 . 7 10 4 3 0 2 1.14 4.1 2 0 6 6 0 1 1.92 6 .9 4 0 Table 1.1 Noise level and detection limits at a 99% confidence level based on numerical simulations of the MOST microsatellite (after Matthews & Kuschnig 2000a). 1.4.1 The M O S T C C D M O S T w i l l u s e t w o i d e n t i c a l C C D s i n the f o c a l p l a n e ; the d e v i c e s are c u s t o m p a c k a g e d v e r s i o n o f t h e 4 7 - 2 0 t y p e b u i l t b y M a r c o n i ( f o r m e r l y E E V L t d . ) . C C D s p e c i f i c a t i o n s o f the s c i e n c e g r a d e M O S T C C D s are l i s t e d i n T a b l e 1.2 ( F u r t h e r i n f o r m a t i o n o n t h e o f f - t h e - s h e l f m o d e l o f C C D 4 7 - 2 0 is i n A p p e n d i x F ) . N o i s e at 150 K H z 6 .7 r m s e" M e a n D a r k S i g n a l at - 3 0 ° C 16.3 e ' / p i x e l / m i n u t e P e a k S i g n a l 1 1 9 k e 7 p i x e l S e r i a l C T E 0 . 9 9 9 9 9 6 - 1 . 0 0 0 0 0 2 P a r a l l e l C T E 0 . 9 9 9 9 9 8 - 0 . 9 9 9 9 9 7 Q u a n t u m E f f i c i e n c y at 4 0 0 n m 4 4 . 8 % at 5 0 0 n m 8 3 . 0 % at 6 5 0 n m 9 0 . 2 % P i x e l s 1 0 2 4 x 1 0 2 4 P i x e l S i z e 13 x 13 u r n P e a k c h a r g e s t o r a g e 1 2 0 , 0 0 0 e / p i x e l Table 1.2 Description of CCD47-20 and results from testing of the MOST science grade CCD. 12 Gate N-type silicon Oxide layer Channel stop Depletion region P-type silicon Figure 1.6 Schematic of typical buried channel CCD, in inverted mode. In an inverted mode, electron hole pairs accumulate at the silicon oxide interface layer. C C D 4 7 - 2 0 is a 1 0 2 4 x 1024 , b a c k i l l u m i n a t e d d e v i c e , w i t h p i x e l s 13 u m w i d e . T h e C C D s t r u c t u r e is b a s e d o n a p - t y p e , e p i t a x i a l l a y e r o f s i l i c o n a b o u t 1 0 - 2 0 m i c r o n s t h i c k , c o v e r e d b y a n i n s u l a t i n g l a y e r o f s i l i c o n d i o x i d e a b o u t 1 0 0 0 A n g s t r o m s t h i c k . T h i s s t r u c t u r e i s s a n d w i c h e d b e t w e e n the p l a t e s o f a M I S ( M e t a l I n s u l a t e d S e m i c o n d u c t o r ) c a p a c i t o r ( F i g u r e 1.6). T h e C C D 4 7 - 2 0 d e v i c e i s b a c k - i l l u m i n a t e d i n o r d e r to i n c r e a s e q u a n t u m e f f i c i e n c y ( Q E ) , a m e a s u r e o f the rate at w h i c h a n e l e c t r o n i s p r o d u c e d b y i n c o m i n g p h o t o n . T h a t i s , i n o r d e r to p r e v e n t p h o t o n s f r o m b e i n g s t o p p e d b y t h e i n s u l a t i n g o x i d e l a y e r a n d n o t p e n e t r a t i n g i n t o the p - s i l i c o n w h e r e t h e p h o t o e l e c t r i c e f f e c t o c c u r s a n d s i g n a l i s g e n e r a t e d , the C C D is b a s i c a l l y f l i p p e d o v e r a n d t h e p - s i l i c o n s u b s t r a t e is e t c h e d o r t h i n n e d . T h e p - s i l i c o n is t h e n d i r e c t l y i l l u m i n a t e d s o that p h o t o n s g e n e r a t e e l e c t r o n s to b e i m m e d i a t e l y c o l l e c t e d . T h u s , b a c k - i l l u m i n a t e d d e v i c e s g e n e r a t e a g r e a t e r s i g n a l ( i .e . h i g h e r Q E ) . C C D 4 7 - 2 0 i s o p e r a t e d i n a n i n v e r t e d m o d e ( I M O ) a n d u t i l i z e s M P P ( M u l t i - P i n -P h a s e d ) t e c h n o l o g y i n o r d e r to r e d u c e d a r k c u r r e n t . I n a n i n v e r t e d m o d e , t h e s i l i c o n - t o -s i l i c o n - d i o x i d e i n t e r f a c e i s h e l d i n i n v e r s i o n (the p o t e n t i a l i n the gate h i g h a n d e l e c t r o n -h o l e p a i r s a c c u m u l a t e ) . I f t h e v o l t a g e a c r o s s t h e e l e c t r o d e i s l e s s t h a n a b o u t -6 V , t h e b i a s o n the e l e c t r o d e is s u f f i c i e n t l y n e g a t i v e as to attract e l e c t r o n - h o l e p a i r s to t h e o x i d e i n t e r f a c e s u r f a c e . T h e n t h e s u r f a c e is s a i d to b e inverted, a n d the l a y e r c o n t a i n i n g t h e e l e c t r o n h o l e p a i r s i s c a l l e d t h e inversion layer. A s the h o l e s f l o o d t h i s l a y e r , t h e y f i l l t h e i n t e r f a c e states, b l o c k i n g e l e c t r o n s f r o m the i n t e r f a c e r e g i o n a n d t r a p p i n g t h e m i n the b u r i e d c h a n n e l s . T h i s a l s o s e r v e s to r e d u c e the p a t h w a y f o r e l e c t r o n s e x c i t e d t h e r m a l l y 13 f r o m m o v i n g f r o m t h e v a l e n c e b a n d to t h e c o n d u c t i o n b a n d , r e d u c i n g o r e l i m i n a t i n g d a r k c u r r e n t ( S e c t i o n 6 .1 .1) . H o w e v e r , i f t h e e n t i r e p i x e l i s o p e r a t e d i n i n v e r s i o n , t h e n the e l e c t r o n s are n o l o n g e r c o n f i n e d t o t h e i r p i x e l . T o o v e r c o m e t h i s , a n i m p l a n t i s p l a c e d b e l o w o n e o f t h e e l e c t r o d e s . T h e i m p l a n t a l ters the p o t e n t i a l w e l l i n the d e v i c e s u c h that e l e c t r o n s c a n n o t p e n e t r a t e t h r o u g h the r e g i o n u n d e r n e a t h that e l e c t r o d e . T h u s , a p o t e n t i a l b a r r i e r i s set u p b y t h e i m p l a n t a l o n g o n e s i d e o f t h e p i x e l , t r a p p i n g t h e c h a r g e i n s i d e . W i t h t h i s d e v i c e a r c h i t e c t u r e , d a r k c u r r e n t i s s i g n i f i c a n t l y s u p p r e s s e d , a n d c h a r g e p a c k e t s a r e e f f e c t i v e l y s t o r e d i n a s i n g l e p i x e l f o r a s p e c i f i e d i n t e g r a t i o n t i m e . T h e s i l i c o n - s i l i c o n d i o x i d e i n t e r f a c e is a p o o r p l a c e t o s tore a n d / o r t r a n s f e r c h a r g e b e c a u s e o f a h i g h d e n s i t y o f t r a p p i n g states, o r p o t e n t i a l w e l l s w h i c h t e n d to h o u s e e l e c t r o n s o r e l e c t r o n - h o l e p a i r s f o r e x t e n d e d p e r i o d s o f t i m e . T h e t r a p p i n g states s i m p l y a r i s e f r o m a d i s r u p t i o n i n t h e s i l i c o n l a t t i c e s t r u c t u r e . T h u s , C C D s u s u a l l y s tore a n d t r a n s f e r c h a r g e w i t h i n t h e p - t y p e s i l i c o n l a y e r . I n o r d e r to f o r c e the e l e c t r o n s t o d e p t h i n the s t r u c t u r e , t h e p s u r f a c e i s c o a t e d w i t h a s i l i c o n la t t i ce r i c h i n n - t y p e i m p u r i t i e s , o r a n n - t y p e s i l i c o n l a y e r . T h e n - t y p e s i l i c o n i s d o p e d s u c h that it is p o s i t i v e l y b i a s e d w i t h r e s p e c t to t h e p - t y p e l a y e r . H e n c e , e l e c t r o n s a r e c o l l e c t e d a n d t r a n s f e r r e d i n t h e p - t y p e l a y e r , r e m o v e d f r o m t h e s i l i c o n - s i l i c o n d i o x i d e i n t e r f a c e . T h u s , t h i s t y p e o f d e v i c e i s c a l l e d a buried channel device. T h e C C D is t h e m o s t s e n s i t i v e c o m p o n e n t o f t h e M O S T t e l e s c o p e to the o r b i t a l e n v i r o n m e n t . 14 Chapter 2: The Theory behind Space Weather 2.1 History T h e a u r o r a e b o r e a l i s g a v e s c i e n t i s t s the first i m p o r t a n t c l u e s a b o u t c h a r g e d p a r t i c l e m o t i o n i n t h e E a r t h ' s m a g n e t i c field. I n fac t , " c o s m i c " r a d i a t i o n w a s first d e t e c t e d b y B i r k e l a n d i n 1895 i n a v a c u u m c h a m b e r e x p e r i m e n t d e s i g n e d to s t u d y the a u r o r a e b o r e a l i s ( V a n A l l e n 1983) . H o w e v e r , i t w a s a n o t h e r 10 y e a r s b e f o r e it w a s r e c o g n i s e d that the s o u r c e o f i o n i s i n g e n e r g y w a s e x t r a t e r r e s t r i a l , w h e n it w a s o b s e r v e d that t h e a m o u n t o f i o n i z a t i o n i n the c h a m b e r s r o s e w i t h i n c r e a s i n g a l t i t u d e ( c f . K l e c k e r 1996) . B u i l d i n g o n B i r k e l a n d ' s w o r k , a n d m o t i v a t e d to s h o w that the a u r o r a e are g e n e r a t e d b y c h a r g e d e l e c t r o n s a n d i o n s t r a p p e d i n the g e o m a g n e t o s p h e r e , St0rmer e x p l o r e d the t h e o r y o f c h a r g e d p a r t i c l e i n t e r a c t i o n s w i t h a d i p o l e m a g n e t i c field. H e s h o w e d that t h e r e are t w o d y n a m i c a l r e g i o n s i n a d i p o l e m a g n e t i c field, o n e that i s u n b o u n d e d a n d a c c e p t s c h a r g e d p a r t i c l e s f r o m i n f i n i t y , a n d a n o t h e r that i s b o u n d e d a n d t raps c h a r g e d p a r t i c l e s i n d e f i n i t e l y , a radiation belt ( F i g u r e 2 .1) . T h e t w o r e g i o n s h a v e n o o v e r l a p i n the i d e a l St0rmerian c a s e ( V a n A l l e n 1983) . A l t h o u g h S t o r m e r w a s Figure 2.1 Meridian projection of a trapped charged particle (after Van Allen 1983). 15 unsuccessful i n proving that the aurorae were indeed caused by trapped electrons or ions, these advances laid the theoretical framework for magnetospheric particle motion. In the 1930's a group of researchers, including Arthur Compton, Robert M i l l i k a n , W i l l i a m Pickering, Wil lmot Hess, and others, collected ionisation chamber and Geiger counter measurements at various altitudes using balloon-borne instruments. The evidence showed that the radiation emanated from the Sun and had a particulate nature. In 1936 Hess was given the Nobel Prize for his discovery of 'galactic cosmic rays', which we now know to be particles as well . Although the balloon-borne measurements showed increasing cosmic ray radiation up to 30 k m , it was unclear how to extrapolate the results to even higher altitudes. It was this problem which inspired an early U S Rocketry program to investigate high altitude phenomenon, paving the way for the first American artificial satellites to investigate geophysical parameters of the earth. The high-altitude measurements of very early satellites such as Explorer I and III led to the discovery of the " V a n A l l e n " radiation belts of the Earth, much as Stermer had predicted (Van A l l e n 1959). Explorer discovered two radiation belts, and inner and an outer belt, separated by a slot region (Figure 2.2). 2.2 Charged Particle Motion in a Magnetic Field The fundamental motion of a charged particle in a magnetic field is described by the Lorentz equation: Figure 2.2 Artists conception of the Van Allen radiation belts. Inner and outer radiation belts are both shown. F = ^ - = q(vxB + E) dt (2.1) 16 where F is the force on a charged particle due to a magnetic field, p is the momentum of the particle, q is the charge on the particle, v is the velocity of the particle, B is the magnetic field strength, and E is the electric field strength. The momentum p of a charged particle given by: p = mv + qA ^1'T) where A is the vector potential of the magnetic field. For temporally uniform magnetic fields with simple geometry, the solution to equation (2.1) is easily integratable. However, for the magnetic field of the Earth, direct integration is not possible. Instead, the solution must be restricted to regions of space which have approximately uniform and simple magnetic fields where a direct solution is feasable. Models of the radiation environment are usually semi-empirical (i.e. they utilise a combination of theoretical interpretation with experimental data to make predictions). Three basic motions describe the trajectory of a trapped charged particle (Figure 2.3). First, in the absence of electric fields, it is trivial to show the parallel velocity (i.e. velocity along magnetic field lines) is constant, and the magnitude of the perpendicular velocity is constant but with changing direction. Thus, the particle sweeps out a helical pathway around magnetic field lines with gyroradius p (radius of the circular component of motion) defined by equating the centripetal force to the magnetic force: _ mv ~Bq (2.3) 17 S e c o n d , the p a r t i c l e w i l l d r i f t a l o n g m a g n e t i c field l i n e u n t i l i t r e a c h e s a n a r e a o f h i g h e r m a g n e t i c field i n t e n s i t y w h e r e it is m i r r o r e d o r ' b o u n c e d ' i n the o p p o s i t e d i r e c t i o n . A n d t h i r d , i n h o m o g e n e i t i e s i n the E a r t h ' s m a g n e t i c field c a u s e a s l o w w e s t w a r d d r i f t o f p r o t o n s , a n d e a s t w a r d d r i f t o f e l e c t r o n s ( d u e to the o p p o s i t e c h a r g e o n e a c h p a r t i c l e , t h e f o r c e s d u e to the i n h o m o g e n e i t i e s a r e i n o p p o s i n g d i r e c t i o n s ) . T h e s e three m o t i o n s , d i s c u s s e d b e l o w i n t e r m s o f adiabatic invariants, c o n f i n e t r a p p e d p a r t i c l e s to d r i f t s h e l l s . 2.2.1 Adiabatic Invariants I n o r d e r to m o d e l c h a r g e d p a r t i c l e m o t i o n a r o u n d the E a r t h , t h r e e p a r a m e t e r s are c a l c u l a t e d w h i c h q u a n t i f y t h e t h r e e d i f f e r e n t t y p e s o f m o t i o n . I n a n y m e c h a n i c a l s y s t e m w i t h p e r i o d i c m o t i o n w h e r e the c h a n g e s i n t h e f o r c e s a l o n g the p a t h s o f m o t i o n are s l o w , it i s p o s s i b l e to c a l c u l a t e v a l u e s w h i c h r e m a i n c o n s t a n t o v e r t h e p a t h w h e n i n t e g r a t e d o v e r c h o s e n p e r i o d i c o r b i t s . T h e s e are k n o w n as adiabatic invariants. T h e t h r e e a d i a b a t i c i n v a r i a n t s are f o u n d b y i n t e g r a t i n g o v e r o n e g y r a t i o n o r b i t , o n e b o u n c e p e r i o d , a n d o n e p e r i o d i c t r a j e c t o r y r e s p e c t i v e l y . Mirror Point Figure 2.3 Schematic of charged particle motion in the geomagnetic field depicting the three motions of gyration, bouncing, and drift. (After Hess 1968) T h e first a d i a b a t i c i n v a r i a n t i s g i v e n b y t h e f o l l o w i n g s u r f a c e i n t e g r a l o v e r the g y r o p e r i o d a n d a l o n g the h e l i c a l p a r t i c l e t r a j e c t o r y : 18 Jx = §(p + qA)dl _ Tip 2 ~~qB (2.4) 2mB (2.5) p± i s t h e p e r p e n d i c u l a r c o m p o n e n t o f the m o m e n t u m v e c t o r . J j , o r fi, is c a l l e d the m a g n e t i c m o m e n t , a n d d e t e r m i n e s t h e b o u n c e m o t i o n o f t r a p p e d p a r t i c l e s i n t h e m o d e l s . T h e m a g n e t i c f o r c e o n a c h a r g e d p a r t i c l e is p e r p e n d i c u l a r t o t h e f i e l d l i n e d i r e c t i o n . T h u s , t h e m a g n e t i c f o r c e i n a r e g i o n o f h i g h e r m a g n e t i c field s t r e n g t h s e r v e s to i m p a r t m o m e n t u m t o the p a r t i c l e p e r p e n d i c u l a r to t h e field ( i . e . , t o p± ) . T h e r e f o r e , t h e p a r t i c l e ' s p e r p e n d i c u l a r m o m e n t u m s q a u r e d to m a g n e t i c field r a t i o i s c o n s t a n t . H o w e v e r , i n a q u i e s c e n t field ( a field that i s t e m p o r a l l y s t a b l e ) t o t a l m o m e n t u m is s t i l l c o n s e r v e d , s o t h e p a r a l l e l m o m e n t u m o f the p a r t i c l e d r o p s to z e r o . T h e p o i n t w h e r e t h e p a r a l l e l m o m e n t u m is z e r o is d e f i n e d as the m i r r o r p o i n t ( B m ) , b e c a u s e the p a r t i c l e is t h e n r e f l e c t e d o u t o f the r e g i o n o f h i g h e r m a g n e t i c i n t e n s i t y a n d ' m i r r o r s ' its m o t i o n to the o t h e r m a g n e t i c p o l e . B m f o r a p a r t i c l e at a n y p o i n t a l o n g its t r a j e c t o r y c a n b e f o u n d b y c o n s i d e r i n g the p i t c h (a) o f t h e p a r t i c l e . A s the p a r t i c l e m o v e s to h i g h e r m a g n e t i c i n t e n s i t y , the p i t c h o f the p a r t i c l e w i l l i n c r e a s e to 9 0 ° . T h u s , B m c a n b e f o u n d i f t h e p i t c h a n d m a g n e t i c field is k n o w n f o r a n y o t h e r p o i n t a l o n g the p a r t i c l e ' s p a t h , a n d b y u s i n g t h e first a d i a b a t i c i n v a r i a n t as f o l l o w s : 2 2 • 2 / \ p, p s i n (a) ± ± = — oc J, (2.7) B B 19 T h e f i r s t a d i a b a t i c i n v a r i a n t a l s o r e l a t e s to the g y r o r a d i u s . S u b s t i t u t i n g e q u a t i o n (2 .2 ) i n (2 .5 ) y i e l d s : T h u s , s t r o n g e r m a g n e t i c f i e l d s t r a p p a r t i c l e s w i t h a h i g h e r p e r p e n d i c u l a r m o m e n t u m a n d s m a l l e r g y r o r a d i u s . T h e first a d i a b a t i c i n v a r i a n t i n t r o d u c e s a s e c o n d p e r i o d i c m o t i o n o f t h e p a r t i c l e , t h e b o u n c e p e r i o d ( t i m e it t a k e s f o r the p a r t i c l e to g o f r o m a m i r r o r p o i n t i n t h e n o r t h to a m i r r o n p o i n t i n t h e s o u t h ) . B y i n t e g r a t i n g o v e r t h e b o u n c e p e r i o d a n d a l o n g ds ( the s u r f a c e d e f i n e d b y t h e field l i n e ) t h e s e c o n d a d i a b a t i c i n v a r i a n t is f o u n d . It i s e q u i v a l e n t to t h e i n t e g r a l o f the p a r a l l e l m o m e n t u m o v e r a field l i n e b e t w e e n the t w o m i r r o r p o i n t s , ± B m , a n d d e f i n e d b y : T h e s e c o n d a d i a b a t i c i n v a r i a n t , a l s o c a l l e d t h e i n t e g r a l i n v a r i a n t (I), d e f i n e s d r i f t s h e l l s i n t h e a s s y m e t r i c g e o m a g n e t i c field. A s p a r t i c l e s m i r r o r b a c k a n d f o r t h , t h e y c a n d r i f t a l o n g l i n e s o f c o n s t a n t m a g n e t i c field s t r e n g t h , o r d r i f t i n l o n g i t u d e i n the d i r e c t i o n s p e c i f i e d b y t h e i r c h a r g e . W h e n m a g n e t i c field s t r e n g t h i n c r e a s e s w i t h t i m e (as i n a g e o m a g n e t i c s t o r m ) , h i g h e r m a g n e t i c field s t rengths i n c r e a s e t h e m o m e n t u m o f the t r a p p e d p a r t i c l e s . T h e m i r r o r p o i n t s r i s e to h i g h e r e l e v a t i o n s i n o r d e r t o k e e p the i n t e g r a l i n v a r i a n t c o n s t a n t . C o n v e r s e l y , w h e n the m a g n e t i c field s t r e n g t h d e c r e a s e s , t h e p a r t i c l e s w i l l m i r r o r at p o i n t s c l o s e r t o the E a r t h , a n d m a y b e r e m o v e d f r o m t h e r a d i a t i o n b e l t s i f the m i r r o r p o i n t is l o w e n o u g h t o i n c l u d e s i g n i f i c a n t a t m o s p h e r e . T h e t h i r d a d i a b a t i c i n v a r i a n t J ? i s f o u n d b y i n t e g r a t i n g o v e r a t h i r d f u n d a m e n t a l p e r i o d o f m o t i o n , t h e t i m e it t a k e s f o r t h e p a r t i c l e to d r i f t a r o u n d the e a r t h i n t h e d r i f t s h e l l s d e f i n e d b y J2. J3 i s g i v e n b y : P = (2 .9 ) ( 2 . 1 0 ) ( 2 . 1 1 ) 2 0 ^3 = i(p + q4)di = q§B-dS = q<& ( 2 . 1 2 ) w h e r e dl i s the t h e p a t h a l o n g t h e d r i f t s h e l l , dS is a n e l e m e n t o f the s u r f a c e e n c l o s e d b y t h e d r i f t p a t h a n d <D is t h e c o n s t a n t m a g n e t i c f l u x e n c l o s e d b y the d r i f t p a t h . A s l o n g as t h e g e o m a g n e t o s p h e r e i s s t a b l e , p a r t i c l e s w i l l r e t u r n t o the s t a r t i n g p o i n t o f t h e i r d r i f t p a t h . T h i s a d i a b a t i c i n v a r i a n t i s n o t c o n s e r v e d d u r i n g m a g n e t i c s t o r m s . 2.2.2 B and L coordinates W i t h s u c h a c o m p l i c a t e d p a t t e r n o f m o t i o n a n d s o m a n y d e g r e e s o f f r e e d o m i n t h e v a r i a b l e s o f t h e t r a p p e d p a r t i c l e s ( s p e c i e s , e n e r g y , p i t c h , a l t i t u d e , l a t i t u d e a n d l o n g i t u d e ) , i t h a s p r o v e n a d v a n t a g e o u s to p a r a m e t e r i z e the s p e c i e s p o s i t i o n . T h e m o s t p o p u l a r s c h e m e is b a s e d o n M c l l w a i n ' s d i p o l e s h e l l p a r a m e t e r L ( M c l l w a i n 1961) . L d e s c r i b e s t h e p o s i t i o n o f t h e t r a p p e d p a r t i c l e i n t e r m s o f t h e s c a l a r m a g n e t i c f i e l d s t r e n g t h ( B ) , a n d i n t e g r a l a d i a b a t i c i n v a r i a n t (I). I f t w o p a r t i c l e s h a v e t h e s a m e B a n d I v a l u e s , t h e y e x p e r i e n c e t h e s a m e f o r c e s f r o m the m a g n e t i c f i e l d a n d are c o n s t r a i n e d to the s a m e d r i f t s h e l l a b o u t the ear th . H e n c e , L i s w r i t t e n as a f u n c t i o n o f B a n d I ( e q u a t i o n 2 . 1 3 ) a n d d e s c r i b e s the s h e l l s that p a r t i c l e s a r e c o n f i n e d t o b y l a b e l l i n g e a c h s h e l l w i t h a u n i q u e n u m b e r . rI3B\. ( 2 . 1 3 ) B KM j T h e f u n c t i o n F i s a p p r o x i m a t e d n u m e r i c a l l y f o r t h e c o m p l e x m a g n e t i c f i e l d o f the E a r t h ( M c l l w a i n 1961 ) , a n d M is t h e d i p o l e m o m e n t o f the E a r t h ' s m a g n e t i c field ( M = 8 .06 x 10 g a u s s c m ). T h e p o s i t i o n o f a p a r t i c l e i s d e r i v e d e x p l i c i t l y b y k n o w i n g b o t h B a n d L f o r t h e p a r t i c l e . 21 " N ^ Magnetosheath boundary Collisionless Shock Fronf Figure 2.4 Schematic of the Earth's geomagnetosphere. (After Hess 1968) 2.3 The Geomagnetosphere T h e b o u n d a r y o f the E a r t h ' s m a g n e t o s p h e r e ( c a l l e d the magnetopause) i s f o r m e d w h e r e t h e E a r t h ' s m a g n e t i c f i e l d m e e t s a n d i n t e r a c t s w i t h t h e s o l a r w i n d ( F i g u r e 2 .4) . A s the c h a r g e d p a r t i c l e s o f t h e s o l a r p l a s m a b o m b a r d the E a r t h ' s m a g n e t i c f i e l d at the m a g n e t o p a u s e , 9 9 . 9 % o f the p a r t i c l e s are d e f l e c t e d a r o u n d the E a r t h ( B a r t h 1997) . T h e l e a d i n g e d g e o f t h e E a r t h ' s m a g n e t i c field i s c o m p r e s s e d a g a i n s t the c o l l i s i o n l e s s s h o c k o f t h e s o l a r w i n d , a n d the s t r e a m i n g p a r t i c l e s s w e e p the m a g n e t i c field l i n e s o f the E a r t h o u t w a r d s f r o m t h e s u n , s i g n i f i c a n t l y d i s t o r t i n g t h e m a g n e t i c field f r o m the s i m p l e d i p o l e c o n f i g u r a t i o n set b y the g e o d y n a m o . T h e o u t e r m a g n e t i c field a n d t r a n s i t i o n r e g i o n b e t w e e n the t w o areas h a s a c o m p l i c a t e d a n d d y n a m i c s t r u c t u r e d u e to e x t e r n a l m a g n e t i c field i n t e r a c t i o n s w i t h t h e s o l a r w i n d . L u c k i l y , s i n c e t h e M O S T m i c r o s a t e l l i t e w i l l b e i n L E O , it i s n o t n e c e s s a r y i n t h i s w o r k to f a c e t h e c h a l l e n g e o f c h o o s i n g a m o d e l to r e p r e s e n t t h e e x t e r n a l field. W i t h i n a p p r o x i m a t e l y 5 E a r t h r a d i i , the m a g n e t o s p h e r e is s h i e l d e d f r o m the u p s e t t i n g e f f e c t s o f the s o l a r w i n d a n d is m u c h m o r e s table . T h i s i n n e r r e g i o n is d o m i n a t e d b y t h e m a g n e t i c field o r i g i n a t i n g f r o m t h e c o r e d y n a m o w i t h i n t h e E a r t h . T h e 2 2 c u r r e n t field is m o s t s i m p l y d e s c r i b e d b y a d i p o l e w i t h m a g n e t i c m o m e n t o f f s e t f r o m the r o t a t i o n a l a x i s o f t h e E a r t h b y ~ 1 1 ° , a l t h o u g h t h e field is o n l y q u a s i - d i p o l a r ( w i t h a b o u t 1 0 % o f t h e field e n e r g y i n h i g h e r o r d e r c o n f i g u r a t i o n s ) . F i e l d s t r e n g t h s r a n g e f r o m a f e w n a n o t e s l a s ( n T ) at h i g h a l t i t u d e s to 5 0 , 0 0 0 n T at l o w a l t i t u d e s a n d h i g h l a t i t u d e . T h e E a r t h ' s i n n e r m a g n e t i c field i s n e i t h e r s p a t i a l l y n o r t e m p o r a l l y s table . T h e field s t r e n g t h is d e c r e a s i n g at a n a p p r o x i m a t e rate o f 6 % e v e r y 100 y e a r s , e q u i v a l e n t t o 2 0 n T r e d u c t i o n i n the m a g n e t i c m o m e n t p e r y e a r ( B a r t h 1997) . T h i s i s a s u b s t a n t i a l c h a n g e , b u t s m a l l c o m p a r e d to t h e i n s t a b i l i t y o f t h e o u t e r m a g n e t o s p h e r e w h e r e p e r i o d i c g e o m a g n e t i c s t o r m s u p s e t t h e field l i n e s o n a m u c h s h o r t e r t i m e s c a l e . S i n c e t h e i n n e r m a g n e t i c field is n o n - s t a t i c a n d c h a n g e s i n the field are c u r r e n t l y u n p r e d i c t a b l e , s tatic m o d e l s a r e e m p l o y e d w i t h u p d a t e s r e l e a s e d e v e r y 5 y e a r s b y a n I n t e r n a t i o n a l A s s o c i a t i o n o f G e o m a g n e t i s m a n d A e r o n o m y ( I A G A ) w o r k i n g g r o u p to r e f l e c t c h a n g i n g c o n d i t i o n s n o t e d b y e x p e r i m e n t a l d a t a ( e . g . , M a n d e a et a l . 2 0 0 0 ) . T h e s t a n d a r d r e f e r e n c e m o d e l s a r e b a s e d o n a s p h e r i c a l h a r m o n i c e x p a n s i o n o f the g e o m a g n e t i c p o t e n t i a l i n the f o r m : V = at £ (a /r)" + 1 [g»cos(m0 + O ( 2 1 4 ) H=1TW=0 w h e r e V i s t h e g e o m a g n e t i c p o t e n t i a l , g„m a n d h„m a re m o d e l c o e f f i c i e n t s , a i s t h e m e a n r a d i u s o f t h e e a r t h ( 6 3 7 1 . 2 k m ) , r is t h e r a d i a l d i s t a n c e f r o m the c e n t e r o f t h e E a r t h , <j> is t h e east l o n g i t u d e , 9 i s t h e g e o c e n t r i c c o l a t i t u d e , a n d P„m cos(fT) i s t h e a s s o c i a t e d L e g e n d r e f u n c t i o n o f d e g r e e n a n d o r d e r m. T h e I n t e r n a t i o n a l G e o m a g n e t i c R e f e r e n c e F i e l d ( I G R F ) m o d e l p r o v i d e s a set o f c o e f f i c i e n t s g„m a n d h„m f o r e x p e r i m e n t a l d a t a b a s e d o n a s tat ic m a g n e t i c field i n a g i v e n e p o c h ( M a n d e a et a l . 2 0 0 0 ) . T h u s , t h e r e n o w a set o f ' d e f i n i t i v e ' r e f e r e n c e fields ( D R G F 4 5 , D R G F 5 0 , D R G F 5 5 , D R G F 6 0 , D R G F 6 5 , D R G F 7 0 , D R G F 7 5 , D R G F 8 0 , D R G F 8 5 ) f o r w h i c h the d a t a i s d e f i n i t i v e o n l y i n that n o m o r e c a n b e c o l l e c t e d b e c a u s e w e c a n n o t t r a v e l b a c k i n t i m e . F i e l d m o d e l s f o r the t i m e s b e t w e e n t h e r e f e r e n c e e p o c h s c a n b e l i n e a r l y i n t e r p o l a t e d f r o m t h e e x i s t i n g d a t a . A p p e n d i x B a n d F i g u r e 3 .3 s h o w s t h e r e s u l t i n g B v a l u e s f o r t h e M O S T b a s e l i n e o r b i t . 23 Geographic axis 2.3.1 The South Atlantic Anomaly (SAA) T h e o f f s e t o f the m a g n e t i c d i p o l e a n d the p r e s e n c e o f h i g h e r o r d e r t e r m s i n the s p h e r i c a l h a r m o n i c r e p r e s e n t a t i o n o f the m a g n e t i c f i e l d c a u s e s t h e V a n A l l e n r a d i a t i o n b e l t s t o b e a s y m m e t r i c a b o u t t h e E a r t h ( F i g u r e 2.5) . T h e b e l t s e x t e n d to m u c h l o w e r a l t i t u d e s o v e r a l a r g e r e g i o n c e n t e r e d o n the S o u t h P a c i f i c , c a l l e d t h e S o u t h A t l a n t i c A n o m a l y ( S A A ) . T h e S A A is the m o s t s i g n i f i c a n t f e a t u r e o f r a d i a t i o n e n v i r o n m e n t i n L E O . T h e S A A is a d i p i n t h e f i e l d s t r e n g t h o f t h e E a r t h ' s m a g n e t i c f i e l d o v e r the S o u t h A t l a n t i c O c e a n o f f o f t h e c o a s t o f B r a z i l . T h i s i s d u e to the p h y s i c a l o f f s e t o f the m a g n e t i c a x i s o f the d i p o l e m o m e n t o f the E a r t h ' s a x i s f r o m t h e g e o g r a p h i c a x i s b y 2 8 0 m i l e s , as w e l l as t h e i n c l i n a t i o n o f t h e a x i s b y ~ 1 1 ° T h e m a g n e t i c f i e l d s t r e n g t h i n the S A A d r o p s to b e l o w 0.2 G a u s s at 8 0 0 k m , c r e a t i n g a n a t u r a l f u n n e l f o r t r a p p e d m a g n e t o s p h e r i c p a r t i c l e s . T h e r e h a s b e e n a ( p r i m a r i l y ) n o r t h w e s t w a r d 'dr i f t ' o f the S A A ( D y e r et a l . 1999) . T h e d r i f t is d u e to s e c u l a r d e c r e a s e i n the d i p o l e t e r m o f the E a r t h ' s m a g n e t i c f i e l d ( L a u r i e n t e et a l . 1996) . T h e d r i f t is n o t a Figure 2.5 Schematic slice through the Earth showing the offset in magnetic axis and resulting South Atlantic Anomaly (SAA). Location Year Longitude Latitude of of Centroid Centroid Surface 1970 -26.2 -49.9 Surface 1993 -27.4 -54.1 1336 km 1970 -18.8 -45.1 1336 km 1993 -18.7 -50.1 Table 2.1 Location of centroid of minimum of SAA between 1970 and 1993 (Lauriente etal., 1996) m o t i o n o f the e n t i r e m a g n e t i c f i e l d as a w h o l e , b u t a c h a n g e i n t h e l o c a t i o n o f the b r o a d i r r e g u l a r l y s h a p e d c e n t r o i d o f m i n u m u m f i e l d i n t e n s i t y a s s o c i a t e d w i t h the S A A , a n d v a r i e s w i t h a l t i t u d e ( T a b l e 2 .1) . H o w e v e r , the d e f i n i t i v e b o u n d a r i e s o f 2 4 t h e S A A are k n o w n to b e d i f f e r e n t t h a n o b s e r v e d i n the past as i n d i c a t e d b y r e c e n t m a p p i n g s o f the S A A b y sa te l l i te m i s s i o n s s u c h as t h e H u b b l e S p a c e T e l e s c o p e ( H S T ) a n d t h e F a r - U l t r a v i o l e t S p e c t r o s c o p i c E x p l o r e r ( F U S E ) ( F u l l e r t o n , p r i v a t e c o m m u n i c a t i o n 2 0 0 0 ) . 2.3.2 Geomagnetospheric Shielding T h e g e o m a g n e t o s p h e r e s e r v e s as a n a t u r a l r a d i a t i o n s h i e l d f o r s p a c e c r a f t i n L E O . T h e d e g r e e t o w h i c h t h e m a g n e t o s p h e r e w i l l b e a b l e to s t o p a n i n c o m i n g p a r t i c l e f r o m e n t e r i n g t h e t r a p p i n g r e g i o n s o f t h e m a g n e t i c f i e l d w i l l d e p e n d o n b o t h the m o m e n t u m a n d c h a r g e o f t h e i n c o m i n g p a r t i c l e , a n d its a r r i v a l d i r e c t i o n . T h e d e g r e e o f p e n e t r a t i o n o f a n y g i v e n p a r t i c l e i s d e s c r i b e d b y t h e magnetic rigidity o f t h e p a r t i c l e r, a n d t h e cutoff rigidity ( o r S t d r m e r r i g i d i t y ) o f t h e m a g n e t i c f i e l d rs. I n a d i p o l e f i e l d , the m a g n e t i c r i g i d i t y ( i n g i g a v o l t s , o r G V ) i s a p r o p e r t y o f t h e p a r t i c l e ' s e n e r g y E, a t o m i c m a s s A ( i n a m u ) , a n d c h a r g e z: M o is e q u a l to 9 3 1 M e V . I n t u i t i v e l y , i t is e a s y to see that i f the p a r t i c l e ' s r a t i o o f m a s s t o c h a r g e i s l o w , t h e n it w i l l b e d e f l e c t e d m o r e e a s i l y . E l e c t r o n s h a v e the l o w e s t m a s s to c h a r g e r a t i o , f o l l o w e d b y p r o t o n s . T h u s , f o r a g i v e n e n e r g y , h e a v y i o n s w i l l p e n e t r a t e t h e g e o m a g n e t i c f i e l d t h e f u r t h e s t , a n d e l e c t r o n s w i l l b e d e f l e c t e d the m o s t . H o w e v e r , i f t h e p a r t i c l e h a s s u f f i c i e n t l y h i g h e n e r g y it w i l l s t i l l p e n e t r a t e t h e s h i e l d as h i g h e n e r g y p a r t i c l e s h a v e h i g h m a g n e t i c r i g i d i t y . S t d r m e r d e s c r i b e d cutoff rigidity i n h i s e a r l y w o r k o n the a u r o r a e f o r a s i m p l e d i p o l e m a g n e t i c f i e l d ( B a r t h , 1997) . A l t h o u g h t h e c a s e i s o v e r s i m p l i f i e d , it i s a g o o d s t a r t i n g p o i n t . U s i n g g e o m a g n e t i c l a t i t u d e X, z e n i t h a n g l e e, a n d a z i m u t h a l a n g l e f r o m t h e m a g n e t i c n o r t h p o l e <j> to d e s c r i b e a r r i v a l d i r e c t i o n o f the p a r t i c l e , the c u t t o f f r i g i d i t y rs ( i n G V ) is g i v e n b y : ( 2 . 1 5 ) z M cos4 X R (l + ^ l - s i n ^ sin^cos3 X)1 ( 2 . 1 6 ) 2 5 w h e r e M i s the m a g n e t i c d i p o l e m o m e n t o f t h e f i e l d , a n d R i s the d i s t a n c e f r o m t h e d i p o l e c e n t e r o f t h e E a r t h i n E a r t h r a d i i . I f t h e m a g n e t i c r i g i d i t y o f t h e p a r t i c l e ( e q u a t i o n 2 .15 ) i s l e s s t h a n the c u t o f f r i g i d i t y o f t h e g e o m a g n e t i c f i e l d , t h e n t h e p a r t i c l e w i l l b e d e f l e c t e d a w a y f r o m t h e E a r t h . A g a i n , i n t u i t i v e l y it's c l e a r that a s t r o n g e r m a g n e t i c f i e l d w i l l d e f l e c t m o r e p a r t i c l e s . L e s s o b v i o u s l y , e q u a t i o n ( 2 . 1 6 ) d e m o n s t r a t e s t h e r i g i d i t y d e c r e a s e s w i t h i n c r e a s i n g g e o m a g n e t i c l a t i t u d e . It i s f o r t h i s r e a s o n that c h a r g e d p a r t i c l e s f r o m l a r g e s o l a r e v e n t s a r e bet ter a b l e to p e n e t r a t e i n t o s o u t h e r n a n d n o r t h e r n g e o g r a p h i c l a t i t u d e s t o c a u s e t h e a u r o r a e . I n r e a l i t y , t h e d i p o l e a p p r o x i m a t i o n i s n o t s u f f i c i e n t to c a l c u l a t e c u t o f f r i g i d i t i e s f o r t h e E a r t h ' s m a g n e t i c f i e l d , a n d m o r e c o m p l i c a t e d m o d e l s are u s e d . 2.3.3 Geomagnetic Storms T h e g e o m a g n e t o s p h e r e i s n o n - s t a t i c , w i t h l o n g t e r m s e c u l a r v a r i a t i o n s d u e t o t h e g e o d y n a m o b u t m u c h l a r g e r r a p i d v a r i a t i o n s d u e t o the s o l a r w i n d . S o l a r - m o d u l a t e d c h a n g e s i n t h e E a r t h ' s m a g n e t i c f i e l d are d u b b e d m a g n e t i c s t o r m s . S o l a r w i n d v a r i a t i o n s are d u e p r i m a r i l y to s o l a r f l a r e s a n d c o r o n a l m a s s e j e c t i o n s ( C M E s ) . C M E s are l a r g e e r u p t i o n s f r o m t h e c h r o m o s p h e r e o f the s u n that e jec t u p to 1 b i l l i o n m e t r i c t o n s o f m a t e r i a l at s p e e d s a v e r a g i n g 4 0 0 - 7 0 0 k m / s ( Z i r i n 1988 ) , b u t as h i g h as 2 0 0 0 k m / s ( A l p e r t 2 0 0 0 ) . T h e y s t e m f r o m a n i m b a l a n c e i n m a g n e t o h y d r o s t a t i c e q u i l i b r i u m i n t h e s u n , w h e r e m a g n e t i c f i e l d l o o p s a n d a r c h e s b e c o m e t a n g l e d i n a n i n c r e a s i n g m a g n e t i c f i e l d b a c k g r o u n d . T h e m a g n e t i c s t r u c t u r e s e x p a n d a n d ac t l i k e p i s t o n s o n t h e c o r o n a l p l a s m a p r o d u c i n g f l o w s a n d s h o c k w a v e s ( S t e p a n o v a & K o s o v i c h e v 2 0 0 0 ) . T h e s h o c k f r o n t h i t s t h e m a g n e t o p a u s e o f t h e e a r t h a b o u t 2 d a y s la ter , d r a g g i n g t h e m a g n e t i c f i e l d l i n e s o f t h e E a r t h a n d c o m p r e s s i n g t h e f r o n t e n d o f t h e m a g n e t o s p h e r e . I n o b s e r v a t i o n s m a d e b y L u i et a l . ( 2 0 0 0 ) , t h e m a g n e t o p a u s e w a s c o m p r e s s e d t o w i t h i n g e o s t a t i o n a r y o r b i t s . W h i l e C M E ' s i n c r e a s e t h e v e l o c i t y o f t h e s o l a r w i n d , s o l a r f l a r e s i n c r e a s e the d e n s i t y o f t h e s o l a r w i n d . F l a r e s are c r e a t e d i n the s o l a r p h o t o s p h e r e ( i n t e r i o r to t h e c h r o m o s p h e r e ) d u r i n g m a g n e t i c b r e a k i n g ( w h e n m a g n e t i c f i e l d l i n e s o f the s u n are t w i s t e d , b r e a k o p e n , a n d r e - c o n n e c t i n a l o w e r e n e r g y c o n f i g u r a t i o n ) . T h e e n e r g y f r o m m a g n e t i c b r e a k i n g i n c r e a s e s t h e e n e r g y o f p a r t i c l e s i n the s o l a r w i n d . W h i l e f l a r e s m a y 2 6 u p s e t r a d i o c o m m u n i c a t i o n s a n d are a n i m p o r t a n t m o d u l a t o r to a t m o s p h e r i c d r a g , C M E s h a v e a h i g h e r c o r r e l a t i o n w i t h l a r g e g e o m a g n e t i c d i s t u r b a n c e s . C M E s a n d f l a r e s o c c u r s i m u l t a n e o u s l y d u r i n g the l a r g e s t s o l a r e v e n t s . T h e i n t e n s i t y o f t h e g e o m a g n e t i c s t o r m d e p e n d s o n the o r i e n t a t i o n a n d s t r e n g t h o f t h e C M E . T h e r e w e r e o n a v e r a g e 0 .9 C M E s p e r d a y d u r i n g t h e 1 9 7 4 s o l a r m a x i m u m , a n d 0 .74 p e r d a y d u r i n g t h e s u b s e q u e n t s o l a r m i n i m u m i n 1 9 8 0 , b u t o n l y as m a n y as - 7 0 % o f t h e s e are a s s o c i a t e d w i t h i n t e r p l a n e t a r y s h o c k f r o n t s ( Z i r i n 1988) . T h e a c t u a l n u m b e r o f C M E s d e c r e a s e s as the s o l a r c y c l e d e c r e a s e s , b u t the f r a c t i o n o f t h o s e c r e a t i n g i n t e r p l a n e t a r y s h o c k f r o n t s r e a c h e s a m a x i m u m i m m e d i a t e l y f o l l o w i n g s o l a r m a x i m u m ( L i n d s a y et a l . 1995) . F o r t u n a t e l y , m o s t o f C M E s are d i r e c t e d i n t o e m p t y s p a c e a n d n o t t o w a r d s E a r t h . T h e l a r g e s t g e o m a g n e t i c s t o r m s a r e f r o m a d i r e c t , f a c e - o n i m p a c t o f a C M E ( L u i 2 0 0 0 ) . F u r t h e r m o r e , s i n c e C M E s a r e m a d e o f c h a r g e d p a r t i c l e s a n d a r e n o t e l e c t r i c a l l y n e u t r a l , e a c h C M E h a s a d i f f e r e n t m a g n e t i c o r i e n t a t i o n . I f it i s a s o u t h w a r d o r i e n t a t i o n , t h e n t h e m a g n e t i c f i e l d o f t h e C M E is m o r e e a s i l y c o u p l e d to t h e m a g n e t i c f i e l d o f the e a r t h a n d a v e r y l a r g e d i s t u r b a n c e r e s u l t s ( B a r t h , 1997) . T h u s , g e o m a g n e t i c s t o r m s a r e v e r y h a r d t o p r e d i c t . E v e n w i t h e a r l y w a r n i n g d e t e c t i o n s o f C M E s b y o r b i t i n g s p a c e c r a f t , the i n t e n s i t y o f t h e s t o r m c a n n o t b e k n o w n i n a d v a n c e . S a t e l l i t e s i n g e o s t a t i o n a r y o r h i g h - a l t i t u d e o r b i t s are m o s t h e a v i l y i n f l u e n c e d b y g e o m a g n e t i c s t o r m s . H o w e v e r , i t i s d u r i n g s u c h s t o r m s that p a r t i c l e s are i n j e c t e d i n t o t h e i n n e r r a d i a t i o n b e l t s . T h u s , g e o m a g n e t i c s t o r m s f o r a L E O are a s s o c i a t e d w i t h a s m a l l i n c r e a s e i n c h a r g e d p a r t i c l e b o m b a r d m e n t d u e to a d e c r e a s e i n c u t o f f r i g i d i t y ( i . e . , a n i n c r e a s e i n g e o m a g n e t i c t r a n s m i s s i o n f u n c t i o n , s e c t i o n 3 .1 .3) . 2.4 Charged Particle Populations T h i s d e s c r i p t i o n o f c h a r g e d p a r t i c l e m o t i o n h a s t h u s f a r n e g l e c t e d to c o n s i d e r i n a n y d e t a i l the o r i g i n a l s o u r c e s o f t h e c h a r g e d p a r t i c l e s . T h e r e are f o u r p o p u l a t i o n s o f c h a r g e d p a r t i c l e s that c a n i n t e r a c t w i t h a s p a c e c r a f t : (a) r e s i d u a l m a g n e t o s p h e r i c t r a p p e d p a r t i c l e s , (b) s o l a r e n e r g e t i c p a r t i c l e s ( S E P ) , (c ) G a l a c t i c c o s m i c r a y s ( G C R s ) , a n d (d) a n a n o m a l o u s c o s m i c r a y ( A C R ) c o m p o n e n t . T h e m a i n p r o p e r t i e s d i s t i n g u i s h i n g t h e p o p u l a t i o n s are s u m m a r i z e d i n T a b l e 2 .2 . T h e S u n t u r n s o u t to b e the m o s t i m p o r t a n t f a c t o r , b o t h as a s o u r c e a n d as a m o d u l a t o r o f t h e s e p o p u l a t i o n s . 2 7 P r o p e r t i e s o f the C h a r g e d P a r t i c l e P o p u l a t i o n s (a) M a g n e t o s p h e r i c Particles (b) Solar E n e r g e t i c Particles ( C M E s ) (c) G a l a c t i c C o s m i c R a y s (d) A n o m a l o u s C o s m i c R a y s E n e r g y R a n g e 0.04 - 3 0 0 M e V (protons); .04 ~ 7 M e V (electrons) varies, large events > 4 3 0 M e V n o l imit , u p to 100s G e V / n u p to 100 M e V / n C o m p o s i t i o n protons a n d electrons d o m i n a t e d b y protons, c o r o n a l abundance o f h e a v y i o n s 8 3 % protons, 13 % H e ions, 3 % electrons, a n d 1% heavier n u c l e i enr iched i n elements w i t h large 1st ionisa t ion potential ( H , N , O , N e ) C h a r g e state o f h e a v y i o n s N / A Intermediately charged h e a v y i o n s F u l l y c h a r g e d h e a v y i o n s S i n g l y charged h e a v y i o n s Solar C y c l e M o d u l a t i o n Protons increase d u r i n g solar m a x , electrons decrease d u r i n g solar m a x Increase n u m b e r o f events d u r i n g solar m a x , increase n u m b e r o f C M E s w h i c h cause geomagnet ic storms i n d e c l i n i n g phase Increase d u r i n g solar m a x Increase d u r i n g solar m a x M o d e l s A P 8 / A E 8 J P L 9 1 , C R E M E C R E M E C R E M E Table 2.2 Comparison of trapped particle populations. 2.4.1 Magnetospheric Particles T h e m a g n e t o s p h e r i c p a r t i c l e s a r e c o n s i d e r e d as a separa te p o p u l a t i o n b e c a u s e o f t h e i r l o n g l i f e t i m e . O b s e r v a t i o n s o f a n e w p r o t o n b e l t f o r m e d i n the w a k e o f a v e r y l a r g e s o l a r f l a r e i n M a r c h 1991 s h o w e d that p a r t i c l e s w e r e t r a p p e d a n y w h e r e f r o m 8 m o n t h s to 2 y e a r s ( D y e r et a l . 1996) . T h i s d i s c u s s i o n w i l l c o n c e n t r a t e o n the d y n a m i c s o f m a g n e t o s p h e r i c p a r t i c l e s d u e to v i o l a t i o n o f a d i a b a t i c i n v a r i a n t s ( s e c t i o n 2 .2 .1 ) , i . e . , h o w p a r t i c l e s c a n s e e p i n t o a n d o u t o f the r a d i a t i o n b e l t s . 28 W i t h o u t a s o u r c e o f r e p l e n i s h m e n t , t r a p p e d c h a r g e d p a r t i c l e s i n t h e r a d i a t i o n b e l t s w o u l d e v e n t u a l l y i o n i s e m o l e c u l a r s p e c i e s i n t h e u p p e r a t m o s p h e r e a n d b e r e m o v e d f r o m t h e m a g n e t i c f i e l d o f the ear th . C o n v e r s e l y , w i t h o u t t h e s i n k o f t h e u p p e r a t m o s p h e r e , t r a p p e d p a r t i c l e a b u n d a n c e w o u l d i n c r e a s e c o n t i n u a l l y a s c h a r g e d p a r t i c l e s f r o m t h e s o l a r w i n d g r a d u a l l y l e a k i n t o the t r a p p i n g r e g i o n s o f t h e f i e l d . H e n c e , the stat ic f l u x o f p a r t i c l e s at a g i v e n e n e r g y r e p r e s e n t s a n e q u i l i b r i u m b e t w e e n f o u r c o m p e t i n g p r o c e s s e s : p a r t i c l e l o s s , i n f u s i o n , a c c e l e r a t i o n ( a n i n c r e a s e i n e n e r g y o f the p a r t i c l e ) , a n d d i f f u s i o n . T r a p p e d m a g n e t o s p h e r i c p a r t i c l e s are i n f u s e d i n t o t h e r a d i a t i o n b e l t s f r o m t h e s o l a r w i n d , G a l a c t i c c o s m i c r a d i a t i o n , a n d / o r f r o m c o s m i c r a y a l b e d o n e u t r o n d e c a y ( C R A N D ) ( G a s s e r 1990) . I n t h e i n n e r z o n e , C R A N D t u r n s o u t to b e the d o m i n a n t s o u r c e o f t r a p p e d p a r t i c l e s . A s c o s m i c r a y s h i t t h e u p p e r a t m o s p h e r e , h i g h - e n e r g y n e u t r o n s a r e p r o d u c e d . T h e n e u t r o n s u b s e q u e n t l y d e c a y s a f t e r a h a l f - l i f e o f 6 3 0 s i n t o a p r o t o n a n d e l e c t r o n , w h i c h r e m a i n i n the t r a p p e d i n the r a d i a t i o n b e l t s u n l e s s t h e p a r t i c l e t r a j e c t o r y a n d e n e r g y i s s u c h t h a t t h e y c a n b e c a r r i e d o u t o f t h e m a g n e t o s p h e r e . T r a p p e d p a r t i c l e s a l s o d i f f u s e f r o m the o u t e r m a g n e t o s p h e r e i n t o the i n n e r t r a p p i n g r e g i o n s d u r i n g p e r i o d s o f m a g n e t i c s t o r m s . P a r t i c l e a c c e l e r a t i o n is n o t a w e l l - u n d e r s t o o d p h e n o m e n o n . T h e r e a s o n that a c c e l e r a t i o n is c i t e d as a n i m p o r t a n t p r o c e s s i n the d i s t r i b u t i o n o f m a g n e t o s p h e r i c p a r t i c l e s i s that a n u n s t a b l e r a d i a t i o n b e l t i n b e t w e e n t h e i n n e r a n d o u t e r r a d i a t i o n b e l t s w a s o b s e r v e d i n 1991 b y t h e C R R E S s a t e l l i t e ( B e a u j e a n et a l . 1996) . W i t h i n t h i s n e w r a d i a t i o n b e l t , e l e c t r o n s w i t h e n e r g i e s e x c e e d i n g 10 M e V a n d p r o t o n s w i t h e n e r g i e s e x c e e d i n g 5 0 M e V w e r e d e t e c t e d ( W a l t 1996) . S o m e p r o c e s s m u s t b e r e s p o n s i b l e f o r a c c e l e r a t i n g the t r a p p e d p a r t i c l e s to h i g h e r e n e r g i e s , p r o b a b l y l i n k e d to g e o m a g n e t i c s t o r m s s i n c e a l a r g e C M E i m p a c t e d t h e E a r t h j u s t p r i o r t o f o r m a t i o n o f t h e n e w r a d i a t i o n b e l t s . D i f f u s i o n is p r o b a b l y t h e m o s t i m p o r t a n t o f t h e f o u r c o n t r o l l i n g p r o c e s s e s as it i s d i r e c t l y t i e d to the o t h e r s . T r a p p e d p a r t i c l e d i f f u s i o n m u s t b e cast i n a d i f f e r e n t f o r m t h a n t h e s t a n d a r d d i f f u s i o n e q u a t i o n ( e . g . , g a s d i f f u s i n g d o w n a c o l u m n ) b e c a u s e t h e p a r t i c l e s h a v e t h r e e n o r m a l m o t i o n s ( g y r a t i o n , b o u n c e , a n d d r i f t ) . I n s t e a d , a F o k k e r - P l a n c k p r e s c r i p t i o n is a d o p t e d . I n a F o k k e r - P l a n c k d e r i v a t i o n , d i f f u s i o n is d e s c r i b e d i n t e r m s o f t h e rate o f c h a n g e i n c o - o r d i n a t e s o f t h e p a r t i c l e s ( W a l t 1994) . It i s u s e f u l b e c a u s e the 2 9 c h o i c e o f c o - o r d i n a t e s i s a r b i t r a r y , a d i a b a t i c i n v a r i a n t s as t h e y r e d u c e to three . Figure 2.6 Schematic diagram of radial diffusion in response to a compressed magnetic field. A.) Shell of particles prior to impact with CME. B.) The dotted line represents the position of the old shell and the solid line represents the position after magnetic field compression. C.) Following magnetic relaxation, the particles spread in velocity into a more diffuse shell. (After Walt 1994) C h o i c e o f c o - o r d i n a t e s , i n g e n e r a l , i n v o l v e s t h e t h e d i m e n s i o n a l i t y o f the p r o b l e m f r o m s i x d i m e n s i o n s R a d i a l d i f f u s i o n i s p a r t i c u l a r l y i m p o r t a n t i n the i n n e r r a d i a t i o n b e l t s as it g o v e r n s the t r a n s f e r o f p a r t i c l e s f r o m the o u t e r z o n e to the i n n e r z o n e . S i n c e r a d i a l d i f f u s i o n d e s c r i b e s m o t i o n f r o m o n e d r i f t s h e l l to a n o t h e r , it m a k e s s e n s e that it is r e l a t e d to f l u c t u a t i o n s i n the t h i r d a d i a b a t i c i n v a r i a n t (J3 = q<J>; e q u a t i o n 2 .12 ) f o u n d b y i n t e g r a t i n g o v e r a d r i f t p e r i o d . I n o r d e r f o r J3 to b e v i o l a t e d , c h a n g e s i n the m a g n e t i c f i e l d o r e l e c t r i c p o t e n t i a l f i e l d s m u s t o c c u r o v e r t i m e p e r i o d s m u c h m o r e r a p i d t h a n the d r i f t p e r i o d . D r i f t p e r i o d s r a n g e f r o m a b o u t 1 s e c o n d to 1 d a y ( W a l t 1994) , s o t h i s t y p e o f d i f f u s i o n o c c u r s i n a v a r i e t y o f s c a l e s . T h e m o s t c o m m o n m e c h a n i s m f o r v i o l a t i n g the t h i r d i n v a r i a n t is a g e o m a g n e t i c s t o r m (see s e c t i o n 2 .3 .2 ) . A s a n i l l u s t r a t i o n o f r a d i a l d i f f u s i o n , c o n s i d e r a c o n c e n t r i c s h e l l o f e q u a t o r i a l t r a p p e d p a r t i c l e s i n the E a r t h ' s m a g n e t i c f i e l d as s h o w n i n f i g u r e 2 . 6 a . N o w c o n s i d e r a C M E s h o c k f r o n t s t r i k i n g that s h e l l o f p a r t i c l e s . T h e s h o c k front c o m p r e s s e s t h e m a g n e t i c field t o w a r d s t h e e a r t h , m o s t n o t i c e a b l y a l o n g o n the s h o c k f r o n t i t se l f . I n r e s p o n s e to t h i s a l t e r a t i o n o f the m a g n e t i c field, p a r t i c l e s m o v e t o w a r d s the E a r t h ( F i g u r e 2 . 6 b ) , c h a n g i n g t h e v a l u e o f O , a n d c o n s e r v i n g t h e o t h e r t w o a d i a b a t i c i n v a r i a n t s , ju a n d J2. O n c e the C M E h a s d i s s i p a t e d , the p a r t i c l e s d r i f t a l o n g c o n s t a n t p, J\, a n d <J> a n d g r a d u a l l y f o l l o w t h e r e l a x i n g m a g n e t i c field b a c k to t h e i r o r i g i n a l p o s i t i o n s . T h i s c a u s e s the 3 0 p a r t i c l e s to s p r e a d i n t o d i f f u s e b a n d s d e p i c t e d i n 2 . 6 c . A l t h o u g h t h i s s c e n a r i o i s h i g h l y i d e a l i z e d , t h e m e c h a n i s m f o r t r a n s p o r t i n g t r a p p e d p a r t i c l e s i n t o t h e i n n e r t r a p p i n g r e g i o n is e s s e n t i a l l y the s a m e . P i t c h a n g l e d i f f u s i o n a l s o p l a y s a m a j o r r o l e i n t h e t r a n s p o r t o f e l e c t r o n s o u t o f the r a d i a t i o n b e l t s . It is c a u s e d b y t h e i n t e r a c t i o n o f e l e c t r o n s w i t h p a r t i c l e s i n the E a r t h ' s a t m o s p h e r e , o r b y i n t e r a c t i o n s w i t h e l e c t r o m a g n e t i c w a v e s . T h e lat ter m e c h a n i s m o f l o s s i s i m p o r t a n t o n l y i n t h e o u t e r m a g n e t o s p h e r e w h e r e i n t e r a c t i o n s b e t w e e n t h e m a g n e t o s p h e r e a n d t h e s o l a r w i n d c r e a t e h i g h - e n e r g y e l e c t r o - m a g n e t i c w a v e s . H o w e v e r , i n t h e i n n e r m a g n e t o s p h e r e , a t m o s p h e r i c p a r t i c l e s f r e q u e n t l y c o l l i d e w i t h t r a p p e d p a r t i c l e s . I n d i v i d u a l i n t e r a c t i o n s w i t h e l e c t r o n s d o n o t s i g n i f i c a n t l y a l t e r the p a t h o f the e l e c t r o n , b u t c u m u l a t i v e s c a t t e r i n g w i t h a t m o s p h e r i c p a r t i c l e s c a u s e s a s ta t i s t i ca l c h a n g e i n t h e p i t c h a n g l e s . T h i s r a n d o m p r o c e s s c a n e i t h e r s e n d t h e e l e c t r o n s d e e p e r i n t o the a t m o s p h e r e w h e r e t h e y are e s s e n t i a l l y r e m o v e d f r o m the r a d i a t i o n b e l t s , o r to h i g h e r a l t i t u d e s ( W a l t 1994) . S c a t t e r i n g i s n o t a p p l i c a b l e t o p r o t o n s o r h e a v i e r i o n s b e c a u s e o f t h e i r s u b s t a n t i a l m a s s . H o w e v e r , t h e a t m o s p h e r e i s s t i l l t h e p r i m a r y s i n k f o r t r a p p e d p r o t o n s . A s h i g h -e n e r g y p r o t o n s t r a v e r s e the a t m o s p h e r e , i n e l a s t i c n u c l e a r c o l l i s i o n s e f f e c t i v e l y r e d u c e t h e i r e n e r g y a n d s l o w t h e m d o w n . A 100 M e V p r o t o n c o o l s t o a b o u t 100 k e V af ter 2 2 t r a v e r s i n g 8.6 g m / c m , w h i l e a 1 M e V p r o t o n c o o l s a f ter o n l y " s e e i n g " 0 . 0 0 3 g m / c m o f o x y g e n . B e l o w 100 k e V , p r o t o n s are l o s t i n c h a r g e e x c h a n g e r e a c t i o n s w i t h a t o m i c h y d r o g e n ( H e s s 1968) . T h i s p r o c e s s i s e v e n m o r e e f f i c i e n t at a l o w e r m i r r o r p o i n t o r i n t h e c a s e o f a t m o s p h e r i c i n f l a t i o n . 2.4.2 Solar Energetic Particles C M E s w e r e d i s c u s s e d i n s e c t i o n 2 .3 .2 i n t h e c o n t e x t o f g e o m a g n e t i c d i s t u r b a n c e s . B u t s i n c e a C M E i s a l a r g e m a s s o f c h a r g e d p a r t i c l e s , s o l a r e n e r g e t i c p a r t i c l e s ( S E P ) a r e c o n s i d e r e d as a separa te p o p u l a t i o n w i t h i n the r a d i a t i o n e n v i r o n m e n t . U n t i l t h e m i d - 9 0 ' s , S E P s w e r e t h o u g h t to o r i g i n a t e f r o m s o l a r f l a r e s , as t h e r e i s c o r r e l a t i o n b e t w e e n f l a r e e v e n t s a n d g e o m a g n e t i c s t o r m s . G o s l i n g ( 1 9 9 3 ) d i s p e l s t h i s n o t i o n as t h e ' s o l a r f l a r e ' m y t h a n d p o i n t s to C M E s as t h e r e a l h a z a r d i n t h e r a d i a t i o n e n v i r o n m e n t . 31 T h e r e are n o w t w o t y p e s o f s o l a r e v e n t s d e s c r i b e d i n t h e l i tera ture : gradual a n d impulsive, n a m e d f o r the d u r a t i o n o f x - r a y b u r s t s a s s o c i a t e d w i t h t h e e v e n t s . T h e i m p u l s i v e e v e n t s a r e t y p i c a l l y a s s o c i a t e d w i t h s o l a r f l a r e s a n d are a c c o m p a n i e d b y a n i n c r e a s e i n p a r t i c l e f l u x . T y p i c a l l y , t h e i m p u l s i v e e v e n t s h a v e a n e n h a n c e m e n t i n h e a v y i o n s , a n d a r e d o m i n a t e d b y e l e c t r o n s . T h e i r d u r a t i o n is o n a v e r a g e a f e w h o u r s l o n g ( K l e c k e r 1996) . T h e g r a d u a l e v e n t s a r e s t r o n g l y a s s o c i a t e d w i t h C M E s . T h e C M E p a r t i c l e p o p u l a t i o n i s v e r y s i m i l a r to that o f the s o l a r c o r o n a l a b u n d a n c e , a n d is m u c h m o r e p r o t o n r i c h t h a n the i m p u l s i v e e v e n t ( K l e c k e r 1996) . T h e e v e n t s last s e v e r a l d a y s . S i n c e the C M E e v e n t s are a l s o a s s o c i a t e d w i t h g e o m a g n e t i c d i s t u r b a n c e s , t h e i r e f f e c t s are m o r e s e v e r e t h a n the i m p u l s i v e e v e n t s . C h a r g e d p a r t i c l e s i n the e j e c t i o n c a n d i f f u s e i n t o t h e i n n e r r a d i a t i o n b e l t s d u r i n g t h e p e r i o d o f the s t o r m . H e n c e , e v e n s p a c e c r a f t i n a L E O that a r e s u b s t a n t i a l l y s h i e l d e d b y t h e g e o m a g n e t o s p h e r e a r e s u s c e p t i b l e to these l a r g e r e v e n t s . L u c k i l y , t h e r e are o n l y a b o u t 10 p e r y e a r d u r i n g s o l a r m a x i m u m ( B a r t h 1997) . 2.4.3 Galactic Cosmic Radiation It w a s G a l a c t i c C o s m i c R a d i a t i o n ( G C R ) that H e s s d e t e c t e d i n h i s e a r l y b a l l o o n -b o r n e e x p e r i m e n t s . It i s d e f i n i t e l y e x t r a t e r r e s t r i a l i n n a t u r e (as h e o r i g i n a l l y p r o p o s e d ) a n d is n o w t h o u g h t to e m a n a t e f r o m o u t s i d e the S o l a r S y s t e m , t h o u g h t h e r e i s s t i l l c o n s i d e r a b l e d e b a t e as to t h e s o u r c e o f t h e r a d i a t i o n ( C r o n i n et a l . 1997) . C a s t i n g s u s p i c i o n o n a n i n t e r p l a n e t a r y s o u r c e , G C R e l e m e n t a l a b u n d a n c e p a t t e r n i s e q u a l (to f i r s t o r d e r ) to that f o u n d i n the S o l a r S y s t e m ( T r i b b l e et a l . 1999) . H o w e v e r , it h a s i s o t r o p i c a r r i v a l d i r e c t i o n s , a n d t h u s , p r o b a b l y p e n e t r a t e s t h r o u g h a l l o f i n t e r s t e l l a r s p a c e . F u r t h e r m o r e , t h e e n e r g y s p e c t r u m e x t e n d s t o v e r y h i g h e n e r g i e s ( > 1 0 0 G e V / n u c l e o n ) a n d it is h a r d to f i n d a s o u r c e to a c c e l e r a t e p a r t i c l e s to s u c h h i g h e n e r g i e s w i t h i n t h e S o l a r S y s t e m . I f G C R is i n d e e d g a l a c t i c , i t m u s t t r a v e l t h r o u g h ~ 7 g / c m o f i n t e r s t e l l a r s p a c e ; t h u s , t h e h e a v y i o n p o p u l a t i o n i n the G C R is t h o u g h t t o b e f u l l y i o n i z e d ( c f . B a r t h 1997) . T h e m a j o r i t y o f e x p e r i m e n t s c o n d u c t e d to s t u d y t h e G C R are i n " n e a r - E a r t h i n t e r p l a n e t a r y s p a c e " , s u c h as e x p e r i m e n t s f l o w n o n b o a r d the s p a c e s h u t t l e ( B a d h w a r 1996) . F o r e x a m p l e , the U n i v e r s i t y o f C h i c a g o ' s C o s m i c R a y T e l e s c o p e w a s f l o w n o n f M P - 8 ( i n L E O ) f r o m 1 9 7 6 - 1 9 9 6 to p r o v i d e c o m p l e t e c o v e r a g e o f t h e G C R s p e c t r a o v e r 3 2 a f u l l s o l a r a c t i v i t y c y c l e . V o y a g e r h a s a l s o d e t e c t e d b o t h G C R a n d A C R i n its i n t e r p l a n e t a r y t r a v e l ( R e a m e s 1999) . I n f a c t , a d e c r e a s e i n G C R w i t h d i s t a n c e f r o m t h e S u n i s n o t e d ( B a r t h 1997) . T h e m a j o r d i f f e r e n c e b e t w e e n G C R a n d t h e s o l a r w i n d i s t h e e n e r g i e s o f t h e p a r t i c l e s ; G C R h a s a n e x t r e m e l y h i g h u p p e r e n e r g y l i m i t . T h e e n e r g y r a n g e i s t e n s o f M e V / n t o h u n d r e d s o f G e V / n u c l e o n . H e n c e , t h i s c o m p o n e n t h a s h i g h m a g n e t i c r i g i d i t y a n d p e n e t r a t e s d e e p i n t o the m a g n e t o s p h e r e . C o s m i c r a y s d e t e c t e d b y a s t r o n o m e r s u s i n g g r o u n d - b a s e d t e l e s c o p e s are f r o m the G C R p o p u l a t i o n . T h e t o t a l f l u x o f G C R is s i g n i f i c a n t l y l o w e r t h a n m a g n e t o s p h e r i c p a r t i c l e s . S t i l l , G C R i s a n e x t r e m e l y i m p o r t a n t c h a r g e d p a r t i c l e p o p u l a t i o n b e c a u s e o f t h e h i g h e n e r g i e s o f s o m e o f the i o n s , a n d b e c a u s e o f t h e i r e a s e i n d e p o s i t i n g that e n e r g y i n t o m i c r o e l e c t r o n i c s a n d o t h e r s e n s i t i v e o n b o a r d s p a c e c r a f t c o m p o n e n t s . 2.4.4 The Anomalous Component of Galactic Cosmic Radiation T h e A n o m a l o u s C o m p o n e n t o f R a d i a t i o n ( A C R ) a l s o c o m e s f r o m o u t s i d e o u r S o l a r S y s t e m . H o w e v e r , i ts e l e m e n t a l c o m p o s i t i o n a n d c h a r g e i s d i f f e r e n t f r o m G C R . A l l e l e m e n t s w i t h a l a r g e f i r s t i o n i s a t i o n p o t e n t i a l ( H , N , O , N e ) s h o w a m a r k e d i n c r e a s e i n a b u n d a n c e o v e r t h e G C R ( K l e c k e r , 1996) . T h e c h a r g e s o n the h e a v y i o n s are a l s o d i f f e r e n t f r o m b o t h G C R a n d t h e s o l a r w i n d . A C R is s i n g l y i o n i s e d w h i l e G C R is f u l l y c h a r g e d a n d s o l a r w i n d is i n t e r m e d i a t e l y c h a r g e d . D u e to its p r o p e r t i e s , A C R is t h o u g h t to b e t h e r e s u l t o f r e c y c l i n g o f G C R b y t h e s u n . G C R d i f f u s e s i n t o t h e h e l i o s p h e r e i n t h e S u n w h e r e it i s s i n g l y i o n i s e d b y U V r a d i a t i o n a n d i n t e r a c t i o n s w i t h c h a r g e d s o l a r w i n d s . T h e n it is a c c e l e r a t e d i n t h e h e l i o s p h e r e o r at the o u t e r t e r m i n a t i o n s h o c k a n d r e l e a s e d b a c k i n t o s p a c e . T h i s p o p u l a t i o n h a s e v e n h i g h e r m a g n e t i c r i g i d i t i e s t h a n G C R d u e to its l o w c h a r g e to m o m e n t u m ra t io . B e a u j e a n et a l . ( 1 9 9 6 ) h a v e d e t e c t e d t h e A C R as l o w as L = 1 . 4 - 1 . 6 ( a b o u t 4 0 0 k m a l t i t u d e at the e q u a t o r ) i n the S A A . 33 2.5 Solar Cycle Modulation N o t o n e o f t h e c h a r g e d p a r t i c l e p o p u l a t i o n s i s u n a f f e c t e d b y t h e i n f l u e n c e o f t h e s o l a r c y c l e . S c h w a b e a n n o u n c e d t h e d i s c o v e r y o f a s o l a r ' s u n s p o t ' c y c l e i n 1 8 4 9 w h e n h e n o t i c e d a g r a d u a l r i s e a n d f a l l i n the n u m b e r o f s u n s p o t s o v e r t i m e , as is s h o w n f o r d a t a s i n c e 1 7 5 0 i n f i g u r e 2 .7 ( c f . Z i r i n 1983) . S u n s p o t s a r e o p t i c a l l y d a r k a reas o f t h e S u n a s s o c i a t e d w i t h m a g n e t i c f l u x r o p e s e n t e r i n g a n d e x i t i n g t h e s o l a r p h o t o s p h e r e , a n d h e n c e a p p e a r i n p a i r s o r g r o u p s . T h e p o l a r i t y o f e a c h o f t h e i n d i v i d u a l s p o t s c a n b e o b s e r v e d t h r o u g h t h e Z e e m a n e f f e c t ( H a l e m a d e s u c h o b s e r v a t i o n s i n 1912) . E a c h p a i r i n a g r o u p o f s u n s p o t s h a s o p p o s i n g p o l a r i t y ( Z i r i n 1983) . C o n t i n u o u s m e a s u r e m e n t o f t h e p o l a r i t y o f t h e s u n s p o t s o v e r t h e c o u r s e o f t h e n o t e d 11 y e a r c y c l e s h o w e d that c o n s e c u t i v e c y c l e s d e m o n s t r a t e d a p o l a r i t y r e v e r s a l . H e n c e , the 1 1 - y e a r s o l a r c y c l e i s a c t u a l l y is s u b - c y c l e o f t h e sun 's 2 2 - y e a r m a g n e t i c p o l a r i t y r e v e r s a l p e r i o d . 3 4 Figure 2.7 Sunspot number as a function of date, clearly showing an 11 year periodic solar activity cycle. (Plot is courtesy of David Hathaway, NASA MSFC) A l t h o u g h t h e c o l l o q u i a l q u o t e d s o l a r a c t i v i t y p e r i o d i s 11 y e a r s , t h e a c t u a l d u r a t i o n o f the c y c l e s lasts a n y w h e r e f r o m 9 -13 y e a r s w i t h a n a v e r a g e o f 11.5 y e a r s o v e r t h e p a s t 4 0 y e a r s ( B a r t h 1997) . H e n c e , the c y c l e is u s u a l l y b e s t d e s c r i b e d i n t e r m s o f a 7 y e a r m a x i m u m , i n t e r r u p t e d b y a 4 - y e a r m i n i m u m . T h e d u r a t i o n o f s o l a r m a x i m a d i f f e r s s i g n i f i c a n t l y f r o m c y c l e to c y c l e a n d n o m e a n s o f p r e d i c t i n g t h e d u r a t i o n h a s b e e n f o u n d . S o l a r c y c l e a c t i v i t y h a s o p p o s i t e e f f e c t s o n e l e c t r o n s a n d p r o t o n s . D u r i n g s o l a r m a x i m u m , the s o l a r w i n d is d e n s e r a n d m o r e p a r t i c l e s i o n i s e the E a r t h ' s i o n o s p h e r e . T h i s 35 l e a d s to a s l i g h t , b u t n o t i c e a b l e e x p a n s i o n o f t h e a t m o s p h e r e ( w h i c h c reates g r e a t e r a t m o s p h e r i c d r a g o n o r b i t i n g s a t e l l i t e s ! ) . T h u s , the l o s s o f t r a p p e d p r o t o n s t h r o u g h a t m o s p h e r i c c o l l i s i o n s i s i n c r e a s e d d u r i n g s o l a r m a x i m u m . P e a k p r o t o n f l u x e s o c c u r 1 to 2 y e a r s f o l l o w i n g s o l a r m a x i m u m a n d t h e d e g r e e o f v a r i a t i o n r a n g e s f r o m 5 - 5 0 % b e t w e e n s o l a r m i n a n d s o l a r m a x d e p e n d i n g o n L v a l u e ( H u s t o n et a l . 1998) . W h i l e t h e l o s s o f e l e c t r o n s f r o m t h e i n n e r b e l t s a l s o i n c r e a s e s r e l a t i v e to s o l a r m i n i m u m d u e to a t m o s p h e r i c e x p a n s i o n , t h e i n j e c t i o n o f e l e c t r o n s from the d e n s e r s o l a r w i n d ( s p e c i f i c a l l y d e n s e r i n e l e c t r o n s g e n e r a t e d b y flares) a l s o o c c u r s at a s i g n i f i c a n t l y h i g h e r rate . T h u s , t h e t r a p p e d e l e c t r o n p o p u l a t i o n i n c r e a s e s d u r i n g m a x i m u m s o l a r a c t i v i t y . S i n c e t h e s o l a r w i n d i s s t r o n g e r d u r i n g s o l a r m a x i m u m , G C R is d e f l e c t e d o u t o f the S o l a r S y s t e m m o r e r e a d i l y . H e n c e , s o l a r m a x i m u m a l s o sees a r e d u c t i o n i n b o t h the G C R a n d A C R p o p u l a t i o n s . G C R is d e c r e a s e d b y a f a c t o r o f t h r e e at h i g h l a t i t u d e s d u e to s o l a r m o d u l a t i o n ( D y e r 1999) . T h e A C R p o p u l a t i o n i s r e d u c e d m o r e , b y a f a c t o r o f 100 d u r i n g s o l a r m i n i m u m ( K l e c k e r 1996) . - H o w e v e r , S E P flux i n c r e a s e s . S o l a r m a x i m u m m a r k s t h e p e a k n u m b e r o f i m p u l s i v e a n d g r a d u a l e v e n t s . T h e r e a r e u p t o 1 0 0 0 i m p u l s i v e e v e n t s p e r y e a r d u r i n g s o l a r m a x i m u m a n d o n l y a f e w d u r i n g s o l a r m i n i m u m ( K l e c k e r 1996) . T h e r e are o n l y a b o u t 10 g r a d u a l e v e n t s d u r i n g s o l a r m a x i m u m ( u s u a l l y i n the d e c l i n i n g p h a s e ) a n d t h e r e i s n o e v i d e n c e f o r o n e o c c u r r i n g d u r i n g s o l a r m i n i m u m ( a l t h o u g h it m i g h t h a p p e n i n t h e f u t u r e ) . S i n c e S E P e v e n t s c a u s e g e o m a g n e t i c s t o r m s , g e o m a g n e t i c a c t i v i t y h i g h l y c o u p l e d to t h e s o l a r c y c l e . 36 Currently, the Sun is currently entering solar maximum. SOHO has seen an increase in C M E events. Current sunspot number and predicted sunspot number for the next 7 years are shown in Figure 2.8. • 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 p 1 1 1 1 1 r 1 f Updated October 1999 NASA/Marshall Space Flight Center 1 1998 1898 2908 2002 2004 2008 YEAR Figure 2.8 Recent sunspot data and the 'forecast' of the solar activity cycle for the next decade, (http://science.nasa.gov/newhome/headlines/astl4oct99_l.htm) 3 7 Chapter 3: Modeling the Radiation Environment 3.1 Approach T h e s t a n d a r d a p p r o a c h to m o d e l i n g t h e s p a c e r a d i a t i o n e n v i r o n m e n t i s o u t l i n e d i n F i g u r e 3 .1 . T h i s a p p r o a c h i s r e c o m m e n d e d b y the R a d i a t i o n P h y s i c s O f f i c e ( R P O ) , a d i v i s i o n o f t h e N A S A G o d d a r d S p a c e F l i g h t C e n t e r ( G S F C ) a m o n g s t o t h e r s ( h t t p : / / r a d h o m e . g s f c . n a s a . g o v / r a d h o m e / r p o . h t m , L a B e l 1996) . T h e f i rs t s t e p i s t o d e t e r m i n e the a p p r o p r i a t e o r b i t a l p a r a m e t e r s f o r the m i s s i o n s u c h that its s c i e n t i f i c g o a l s c a n b e m e t . T h e o r b i t a l e n v i r o n m e n t f o r t h e b a s e l i n e p a r a m e t e r s i s e v a l u a t e d u s i n g a s u i t e o f n u m e r i c a l p r o g r a m s , e a c h d e s i g n e d to c a l c u l a t e a v e r y s p e c i f i c c o m p o n e n t o f the r a d i a t i o n e n v i r o n m e n t o r o t h e r e n v i r o n m e n t a l e f f e c t , b a s e d o n t h e t h e o r e t i c a l f r a m e w o r k d e v e l o p e d i n C h a p t e r 2. T h i s c h a p t e r p r e s e n t s a d e s c r i p t i o n o f the n u m e r i c a l m o d e l s i n c o r p o r a t e d i n S P A C E R A D I A T I O N 4.00*. C h a p t e r 4 p r e s e n t s t h e r a d i a t i o n e n v i r o n m e n t o f the M O S T m i c r o s a t e l l i t e a n d i n t e r p r e t a t i o n o f the e n v i r o n m e n t a l e f f e c t s o n t h e M O S T m i c r o s a t e l l i t e d e s i g n . * SPACE RADIATION 4.00 provided courtesy of Alfred Ng, Canadian Space Agency 38 C R E M E JPL 1991 S H I F T , D O S E 1GRJ-Space Pro ject Input J O r b i t G e n e r a t i o n C a l c u l a t e B & L Values m I ralues I C o s m i c R a y Ions Solar F lare Protons T J A p p l y geomagnet ic s h i e l d i n g 1 4 A L L M A G G D A L M G L I N T R A T r a p p e d Part ic les 1 A P S A 1:8 Spacecraft Incident F l u e n c e 1 Transport t h r o u g h s h i e l d i n g J S i m p l e sh ie ld ing geometries 1 J C o m p l e x 3 - D m o d e l o f spacecraft J D i s p l a c e m e n t dose Tota l I o n i s i n g D o s e L E T spectra S i n g l e E v e n t Ef fec ts * A s s e s s m e n t o f Ef fec ts R e c o m m e n d a t i o n s f o r f l ight J Figure 3.1 Schematic of approach to modeling radiation environment for the MOST microsatellite. Routines for specific calculations are indicated in light blue. 3 9 3.2 AP8/AE8 Trapped Particle Models T h e m o s t w i d e l y u s e d m o d e l s f o r e v a l u a t i n g t h e t r a p p e d p a r t i c l e e n v i r o n m e n t s are A E 8 a n d A P 8 f o r e l e c t r o n s a n d p r o t o n s r e s p e c t i v e l y . T h e s e m o d e l s w e r e d e v e l o p e d b y J a m e s V e t t e i n a j o i n t p r o g r a m s p o n s o r e d b y N A S A a n d t h e U S A i r F o r c e ( U S A F ) , a n d i n c o - o p e r a t i o n w i t h v a r i o u s u n i v e r s i t y t e a m s a n d c o r p o r a t i o n s w i t h d a t a o n t h e t r a p p e d p a r t i c l e r a d i a t i o n e n v i r o n m e n t ( V e t t e 1956) . T h e f i rs t m o d e l s ( A E 1 a n d A P I ) w e r e r e l e a s e d i n the e a r l y 60 's , b u t i n c l u d e d o n l y d a t a from s o l a r m i n i m u m a n d t h u s w e r e n o t p r a c t i c a l f o r m o d e l i n g t h e w o r s t c a s e e n v i r o n m e n t s a sa te l l i te w o u l d face* . T h e c u r r e n t l y u s e d v e r s i o n s o f A E 8 a n d A P 8 ( r e l e a s e d i n 1983 a n d 1 9 7 6 ) i n c o r p o r a t e d a t a f r o m 4 3 sa te l l i tes a n d are a p p l i c a b l e to b o t h the m a x i m u m a n d m i n i m u m states o f s o l a r a c t i v i t y . I n 1 9 7 6 , f u n d i n g f o r f u r t h e r m e a s u r e m e n t s w a s r e d u c e d s o t h e m o d e l s that s p a c e c r a f t b u i l d e r s r e l y o n t o d a y are b a s e d o n d a t a f r o m 1 9 5 8 - 1 9 6 8 ( P a n a s y u k 1996) . T h e m o d e l s a r e e m p i r i c a l m o d e l s f o r s ta t ic c o n d i t i o n s . B a s e d o n d a t a f r o m the a b o v e - m e n t i o n e d p e r i o d , t h e f l u x o f p a r t i c l e s o f a g i v e n e n e r g y a n d L v a l u e a r e k n o w n e v e r y w h e r e a l o n g t h e g e o m a g n e t i c e q u a t o r . B a n d L v a l u e s f o r a c h o s e n m a g n e t i c f i e l d are e x t r a p o l a t e d f r o m t h e s p h e r i c a l e x p a n s i o n c o e f f i c i e n t s o f t h e g e o m a g n e t i c p o t e n t i a l b y a s u i t e o f t h r e e i n t e g r a t e d p r o g r a m s d e v e l o p e d b y A l V a m p o l a ( V a m p o l a 1996) : A L L M A G , G D A L M G , a n d L I N T R A ( F i g u r e 3 .3 , A p p e n d i x B ) . T h e r a t i o o f the g e o m a g n e t i c f i e l d s t r e n g t h t o that at t h e g e o m a g n e t i c e q u a t o r , B / B 0 j i s c a l c u l a t e d f o r t h e o r b i t a l t r a j e c t o r y s p e c i f i e d . T h e n , f r o m the g e o m a g n e t i c e q u a t o r i a l f l u x v a l u e s , t h e g e o m a g n e t i c f l u x v a l u e s f o r t r a p p e d p r o t o n s a n d e l e c t r o n s are i n t e r p o l a t e d i n t o B / B 0 a n d L s p a c e a l o n g the o r b i t a l t r a j e c t o r y , a n d i n t e g r a t e d o v e r m i s s i o n l i f e t i m e to p r o d u c e p r o t o n o r e l e c t r o n f l u e n c e s p e c t r a . I n t h e s e m o d e l s , t h e d a t a f r o m o v e r 9 0 e x p e r i m e n t s w a s n o r m a l i z e d to the 1 9 7 6 s t a n d a r d i n g e o m a g n e t o s p h e r i c f i e l d m o d e l s d e v e l o p e d b y J e n s e n a n d C a i n ( G S F C - 1 2 / 6 6 * Intermediate stages of the models also include results from an artificially created electron belt from the Starfish program of high atmosphere nuclear weapon testing. 4 0 d u r i n g s o l a r m a x i m u m , a n d J e n s e n a n d C a i n 1 9 6 0 ( J C 6 0 ) f o r s o l a r m i n i m u m ) i n o r d e r to c a l i b r a t e t h e data . T h u s , m a n y a u t h o r s s u g g e s t that m o r e c u r r e n t r e f e r e n c e m a g n e t i c f i e l d m o d e l s s h o u l d n o t b e u s e d w i t h A E 8 a n d A P 8 ( H e y n d e r i c k x et a l . , 1 9 9 6 , P a n a s y u k , 1 9 9 6 , B a r t h 1 9 9 7 , H u s t o n et a l . , 1998) . T h i s r e c o m m e n d a t i o n w a s e x p l o r e d b y t e s t i n g d i f f e r e n t f i e l d m o d e l s f o r the M O S T b a s e l i n e o r b i t . R e s u l t s a r e p r e s e n t e d i n S e c t i o n 4 .2 . A P 8 a n d A E 8 a l s o i n c l u d e p o s i t i o n a l i n f o r m a t i o n , p a r a m e t e r i z e d i n M c l l w a i n ' s B a n d L v a l u e s ( M c l l w a i n 1961) . 3.3 Geomagnetic Shielding models S P A C E R A D I A T I O N c a l c u l a t e s a g e o m a g n e t i c t r a n s m i s s i o n f u n c t i o n b a s e d o n the S t d r m e r i a n i d e a l d i p o l e t h e o r y (see S e c t i o n 2 .3) . N u m e r i c a l i n t e g r a t i o n o f p a r t i c l e s a l o n g t h e i r t r a j e c t o r i e s i n a n I G R F g i v e s i s o r i g i d i t y c o n t o u r s f o r the v e r t i c a l c u t o f f , i .e . i n d e p e n d e n t o f a z i m u t h a n d z e n i t h a n g l e ( S h e a a n d S m a r t , 1983) . T h e s e r e s u l t s are e x t e n d e d to o m n i d i r e c t i o n a l f l u x b y a s s u m i n g a S t d r m e r i a n d i p o l e f i e l d ( B a r t h , 1997) . T h e r e s u l t i n g f u n c t i o n d e s c r i b e s the f r a c t i o n o f p a r t i c l e s w h i c h c a n p e n e t r a t e the E a r t h ' s m a g n e t i c f i e l d , o r the f r a c t i o n o f p a r t i c l e s w i t h m a g n e t i c r i g i d i t y e x c e e d i n g t h e c u t o f f r i g i d i t y , as a f u n c t i o n o f c u t o f f r i g i d i t y f o r e a c h p o i n t a l o n g t h e o r b i t a l t r a j e c t o r y . A l s o i n c l u d e d i n t h e c a l c u l a t i o n i s t h e e f f e c t o f the E a r t h ' s s h a d o w . A s p a r t i c l e s s t r e a m f r o m t h e s u n t o w a r d s t h e E a r t h , the d a r k s i d e o f t h e E a r t h is n o t o n l y p r o t e c t e d f r o m t h e r a d i a t i o n b y t h e E a r t h ' s m a g n e t i c f i e l d , b u t a l s o b y t h e E a r t h i t se l f . T h u s , the c u t o f f r i g i d i t y i s a s y m m e t r i c a r o u n d the E a r t h i f the E a r t h i s c o n s i d e r e d as a n o b s t a c l e . D u r i n g a s t o r m , the m a g n e t i c r i g i d t y d r o p s o f f . A l a r g e r f r a c t i o n o f l o w e n e r g y p a r t i c l e s a r e t r a n s m i t t e d t h r o u g h the g e o m a g n e t o s p h e r i c s h i e l d i n g . H i g h e n e r g y p a r t i c l e s a r e a t t e n u a t e d b y t h e s a m e a m o u n t i n b o t h c a s e s s i n c e t h e m a g n e t i c r i g i d i t y o f a h i g h e n e r g y p a r t i c l e is a l w a y s g r e a t e r t h a n the c u t o f f r i g i d i t y . 3.4 C R E M E C o s m i c R a y E f f e c t s o n M i c r o - E l e c t r o n i c s ( C R E M E ) w a s d e v e l o p e d b y J a m e s A d a m s a n d o t h e r s f o r the N a t i o n R e s e a r c h L a b o r a t o r i e s ( N R L ) i n the U n i t e d States a n d r e l e a s e d i n 1983 ( T y l k a et a l . 1996) . It w a s t h e f i rs t c o m p r e h e n s i v e n u m e r i c a l c o d e to c a l c u l a t e h e a v i e r c h a r g e d p a r t i c l e p o p u l a t i o n s i n the n e a r - E a r t h e n v i r o n m e n t a n d assess 41 t h e i r i m p a c t o n s p a c e c r a f t e l e c t r o n i c s . A s it i s i n t e g r a t e d i n t o the S p a c e R a d i a t i o n s o f t w a r e , C R E M E i s u s e d t o c a l c u l a t e the f o l l o w i n g c h a r g e d p a r t i c l e s p e c t r a b e h i n d g e o m a g n e t i c a n d s p a c e c r a f t s h i e l d i n g : (a) g a l a c t i c c o s m i c r a y p o p u l a t i o n e n e r g y s p e c t r a ; (b) a n o m a l o u s c o m p o n e n t e n e r g y s p e c t r a ; ( c ) a n d s o l a r e n e r g e t i c p a r t i c l e e v e n t s s p e c t r a . L i k e A P 8 a n d A E 8 , C R E M E i s s e m i - e m p i r i c a l . It u t i l i s e s m e a s u r e d d i f f e r e n t i a l f l u x v a l u e s f o r d i f f e r e n t c h a r g e d h e a v y s p e c i e s ( H - N i ) a n d f i t s the m e a s u r e m e n t s as a f u n c t i o n o f e n e r g y a n d a s i n u s o i d a l s o l a r m o d u l a t i o n p a r a m e t e r . T h e o u t p u t i s the i n t e g r a l o r d i f f e r e n t i a l f l u x o f p a r t i c l e s i n s i d e t h e s p a c e c r a f t at t h e s e n s i t i v e e l e c t r o n i c c o m p o n e n t b e i n g s t u d i e d . T h e d i f f e r e n t i a l flux i s the f r a c t i o n o f e n e r g e t i c p a r t i c l e s i n a g i v e n e n e r g y r a n g e ( E + d E ) d i v i d e d b y t h e e n e r g y b i n s i z e ( d E ) . T h e i n t e g r a l o f t h e d i f f e r e n t i a l f l u x y i e l d s the n u m b e r o f p a r t i c l e s a b o v e a g i v e n e n e r g y ( E ) , the i n t e g r a l flux. C R E M E a l s o e v a l u a t e s A C R ( the v e r y p e n e t r a t i n g s i n g l y i o n i s e d c o m p o n e n t ) . S i n c e t h i s c o m p o n e n t c o m e s f r o m the r e c y c l i n g t h r o u g h t h e s u n , o n l y e l e m e n t s w i t h l a r g e f i r s t i o n i s a t i o n p o t e n t i a l s ( H e , N , O , a n d N e ) are p r e s e n t i n th is t y p e o f r a d i a t i o n . 3.5 Solar Energetic Particles C R E M E i n c l u d e s f o u r m o d e l s t o d e s c r i b e l a r g e s o l a r e n e r g e t i c p a r t i c l e ( S E P ) e v e n t s s t e m m i n g f r o m C M E s . A n a l t e r n a t e m o d e l , J P L 1 9 9 1 , w a s a l s o e m p l o y e d i n t h i s s t u d y ( F e y n m a n n 1993) . T h e m o s t e n e r g e t i c o f t h e flare m o d e l s a r e t h e ' C o m p o s i t e W o r s t C a s e S c e n a r i o ' ( C W C S ) a n d t h e 1972 m o d e l w h i c h i s m o d e l e d af ter o b s e r v a t i o n s o f a v e r y l a r g e S o l a r E n e r g e t i c P a r t i c l e ( S E P ) e v e n t w h i c h o c c u r r e d i n A u g u s t o f 1972 ( A U G 7 2 ) . S i n c e t h e h i g h - e n e r g y c h a n n e l (>60 M e V ) o b s e r v a t i o n s o f t h e 1 9 7 2 e v e n t w e r e u n r e l i a b l e d u e to a n e x c e s s i v e l y h i g h e l e c t r o n b a c k g r o u n d a s s o c i a t e d w i t h the e v e n t ( M a j e w s k i et a l . , 1995 ) , t h e c o m p o s i t e w o r s t c a s e s c e n a r i o h a s a n a d d e d h i g h - e n e r g y t a i l . A t t h e t i m e , t h i s w a s d o n e i n o r d e r to c r e a t e a ' w o r s t c a s e ' S E P w h i c h h a d a 9 9 % c o n f i d e n c e l e v e l ( C L ) that t h e flux d i d n o t e x c e e d a g i v e n v a l u e . A n o t h e r v e r y l a r g e flare e v e n t w a s o b s e r v e d i n g r e a t e r d e t a i l i n O c t o b e r 1 9 8 9 , a n d d i d n o t s h o w t h e h i g h - e n e r g y t a i l o f t h e C W C S , a l t h o u g h 4 2 p e a k p r o t o n f l u x d i d e x c e e d t h e 1972 p e a k p r o t o n f l u x b y a f a c t o r o f 2. T h u s , the C W C S is n o t a u s e f u l w o r s t - c a s e s c e n a r i o m o d e l . T h e A U G 7 2 e v e n t w a s a c t u a l l y a s u c c e s s i o n o f 4 r a p i d C M E s o f ' n o r m a l ' c h a r a c t e r . It a c c o u n t e d f o r 8 4 % o f the p r o t o n f l u e n c e o f h i g h - e n e r g y p a r t i c l e s that y e a r ( K i n g 1974) . T h i s l e d to t h e e a r l y c l a s s i f i c a t i o n o f ' a n o m a l o u s l y l a r g e ' e v e n t s , a n d ' o r d i n a r y ' e v e n t s b y K i n g ( 1 9 7 4 ) . H o w e v e r , F e y n m a n et a l . ( 1 9 9 0 ) r e v i e w e d s o l a r e v e n t d a t a b a s e s a n d c o n c l u d e d that t h e r e is a n i n c r e d i b l e r a n g e o f e n e r g y s p e c t r a a s s o c i a t e d w i t h C M E s , f o r m i n g a c o n t i n u u m i n e n e r g y from l a r g e to s m a l l . T h u s , t h e r e i s n o s u c h t h i n g as a ' t y p i c a l ' S E P a n d s p a c e c r a f t m u s t b e r e a d y f o r t h e w o r s t . T y l k a et a l . ( 1 9 9 7 ) s u g g e s t that t h e t w o m o s t e n e r g e t i c e v e n t s i n c l u d e d w i t h C R E M E a r e u n r e a l i s t i c a l l y s e v e r e . I n d e e d t h e h i g h - e n e r g y t a i l o f t h e C W C S is u n r e a l i s t i c i n that o n l y t h r e e f l a r e e v e n t s o b s e r v e d to d a t e h a v e its e n e r g y d i s t r i b u t i o n . H o w e v e r , s i n c e a l a r g e r S E P t h a n the A U G 7 2 e v e n t w a s o b s e r v e d i n 1 9 8 9 , it i s a p p r o p r i a t e t o c o n s i d e r that e v e n t as the ' w o r s t - c a s e ' m o d e l f o r t h e M O S T m i c r o s a t e l l i t e . N o o t h e r w o r s t c a s e m o d e l s a r e i n c o r p o r a t e d i n t o S p a c e R a d i a t i o n 4 .0 . T h e o t h e r t h r e e s o l a r f l a r e m o d e l s are s i g n i f i c a n t l y m o r e r e a l i s t i c ; t h e y a r e r e p r e s e n t a t i v e o f a v e r a g e S E P e v e n t s d u r i n g s o l a r m a x . T h e 9 0 % w o r s t c a s e C R E M E m o d e l i s a s c a l e d d o w n v e r s i o n o f t h e A u g u s t 1972 e v e n t , w h i l e t h e o r d i n a r y m o d e l is m e a n t to r e f l e c t a n a v e r a g e e n e r g y s p e c t r u m o f m a n y f l a r e s . T h e J P L m o d e l a p p r o a c h e s S E P e v e n t s w i t h a s l i g h t l y d i f f e r e n t p e r s p e c t i v e . I n s t e a d o f i s o l a t i n g s i n g l e e v e n t s , t h e J P L m o d e l a t t e m p t s to s t a t i s t i c a l l y p r e d i c t the l o n g t e r m p r o t o n , H e l i u m , a n d h e a v y i o n d o s e s f o r a g i v e n m i s s i o n , w i t h i n a g i v e n c o n f i d e n c e l e v e l ( C I , o r l e v e l o f c o n f i d e n c e that t h e s o l a r p r o t o n f l u x w i l l n o t e x c e e d the m o d e l v a l u e s ) ( F e y n m a n n et a l . 1993) . T h e J P L 1991 m o d e l w a s u s e d i n t h i s s t u d y as t h e s t a n d a r d , r e a l i s t i c s o l a r p r o t o n m o d e l . O v e r t h e c o u r s e o f a 1 - y e a r m i s s i o n , t h e C L f o r J P L 9 1 i s 9 7 % . H o w e v e r , t h e o t h e r 4 s o l a r p r o t o n m o d e l s w e r e a l s o e v a l u a t e d to a l l o w f o r o n e l a r g e e v e n t d u r i n g t h e M O S T m i s s i o n . T h e d o s e r e s u l t i n g f r o m o n e l a r g e S E P e v e n t o v e r o n e d a y e x c e e d s the y e a r l y d o s e s r e s u l t i n g f r o m u s i n g t h e J P L 9 1 m o d e l . 4 3 3.6 Uncertainties D u e to a p o o r u n d e r s t a n d i n g o f t h e s o l a r a c t i v i t y c y c l e , a n d t h e l i m i t e d p r e d i c t i v e p o w e r s o f l a r g e s o l a r f l a r e s , C M E ' s a n d h e n c e , g e o m a g n e t i c e v e n t s , e v a l u a t i n g t h e u n c e r t a i n t y i n t h e a b o v e m o d e l s i s c h a l l e n g i n g . U n t i l a c c u r a t e p r e d i c t i o n s are m a d e as to t h e t i m i n g , s e v e r i t y , a n d d u r a t i o n o f l a r g e s o l a r e v e n t s , t h e a c c u r a c y o f the i n d i v i d u a l m o d e l s w i l l b e o r d e r s o f m a g n i t u d e bet ter t h a n the a c c u r a c y i n p r e d i c t i n g t h e n u m b e r o f l a r g e S E P e v e n t s a sa te l l i te w i l l f a c e . H e n c e , the s p a c e c r a f t d e s i g n e r is f o r c e d to t a k e a p e s s i m i s t i c v i e w , c o n s i d e r the ' w o r s t - c a s e ' s c e n a r i o , a n d e n s u r e that the sa te l l i te c a n w i t h s t a n d i t ( a n d t h e n c r o s s h e r f i n g e r s that it w o n ' t a c t u a l l y h a p p e n ! ) . H o w e v e r , t h e e x i s t i n g m o d e l s h a v e b e e n i n u s e f o r a s u f f i c i e n t a m o u n t o f t i m e to c o m p a r e p r e d i c t e d d o s e to m e a s u r e d d o s e . G u s s e n h o v e n a n d M u l l e n ( 1 9 9 3 ) i n d i c a t e ' g o o d ' a g r e e m e n t b e t w e e n the A P 8 / A E 8 m o d e l s a n d o r b i t to o r b i t d o s e s as m e a s u r e d b y t h e C o m b i n e d R e l e a s e a n d R a d i a t i o n E f f e c t s S a t e l l i t e ( C R R E S ) . H o w e v e r , t h e y n o t e that p r e d i c t e d f l u x o f h i g h - e n e r g y e l e c t r o n s ( l - 5 M e V ) f r o m A E 8 c a n b e u p to 2 o r d e r s o f m a g n i t u d e t o o h i g h . O n t h e o t h e r h a n d , c o m p a r i s o n s m a d e b y H u s t o n et a l . ( 1 9 9 8 ) w i t h d a t a from the T I R O S / N O A A l o w a l t i t u d e p o l a r o r b i t i n g s p a c e c r a f t i n d i c a t e that A P 8 M I N a n d A P 8 M A X under-predict t h e d o s e e x p e r i e n c e b y a f a c t o r o f 1 .7-2.0 c o n s i s t e n t l y o v e r 2 s o l a r c y c l e s . F a v o r a b l e a g r e e m e n t b e t w e e n A P 8 M I N a n d d a t a o n b o a r d the A d v a n c e d P h o t o v o l t a i c a n d E l e c t r o n i c s E x p e r i m e n t S p a c e c r a f t ( A P E X ) ( i n a h i g h l y e c c e n t r i c 7 0 ° i n c l i n a t i o n o r b i t ) as w e l l as w i t h r e s u l t s f l o w n o n b o a r d P o S A T - 1 ( i n a s u n - s y n c h r o n o u s p o l a r o r b i t v e r y s i m i l a r t o t h e M O S T b a s e l i n e o r b i t ) h a s b e e n f o u n d ( W a t s o n et a l 1 9 9 8 ) . T h e p r e d i c t i o n s f r o m A P 8 M I N o v e r - p r e d i c t t h e A P E X d o s e rates b y 1 0 % , T h e p r i m a r y f a c t o r i n t h e d i s a g r e e m e n t b e t w e e n the m o d e l s a n d the o b s e r v e d d o s e s i s m o s t l i k e l y a n o v e r e s t i m a t i o n o f l o w e n e r g y p r o t o n s . H o w e v e r , t h e m o d e l s u n d e r - p r e d i c t t h e d o s e rates w i t h P o S A T , t h e l o w e r a l t i t u d e sa te l l i te , b y 4 0 % ( D y e r et a l . 1998) . T h u s , t h o u g h the c o l l o q u i a l s t a t e m e n t r e g a r d i n g t h e u n c e r t a i n t y i n t h e A P 8 m o d e l s i s that t h e y o v e r - p r e d i c t the e n v i r o n m e n t , i n t h e l o w a l t i t u d e M O S T b a s e l i n e o r b i t ( S e c t i o n 4 .1 ) , t h e y m o s t l i k e l y u n d e r - p r e d i c t the a c t u a l e n v i r o n m e n t b y a f a c t o r o f a b o u t 2. 4 4 A c c o r d i n g to t h e a u t h o r s o f t h e C R E M E c o d e , the u n c e r t a i n t y i n the C R E M E s p e c t r a r a n g e s f r o m 2-5 d e p e n d i n g o n t h e e n e r g y p e r n u c l e o n ( c f . B a d h w a r a n d O ' N e i l l 1996) . R e c e n t c o m p a r i s o n s o f C R E M E w i t h n e w e r e x p e r i m e n t a l d a t a a n d e x e r c i s e s a s s o c i a t e d w i t h the d e v e l o p m e n t o f a n e w v e r s i o n o f C R E M E ( C R E M E 9 6 ) h a v e s h o w n that the e r r o r s i n the o r i g i n a l m o d e l are o n the o r d e r o f 4 0 % . T h e e r r o r s a r i s e m a i n l y f r o m t h e a s s u m p t i o n that t h e s o l a r a c t i v i t y c y c l e i s s i n u s o i d a l ( T y l k a et a l . 1997) . T h e s o l a r p o l a r i t y r e v e r s a l i s n o t a s i n u s o i d , a n d s o c u r r e n t m o d e l s ( C R E M E 9 6 ) h a v e i n c o r p o r a t e d a m o r e r e a l i s t i c s o l a r m o d u l a t i o n f a c t o r d e v e l o p e d b y N y m m i k ( 1 9 9 6 ) . C o m p a r i s o n w i t h U o S A T - 3 w h i c h a l s o w a s f l o w n i n t h e s a m e o r b i t as t h e M O S T b a s e l i n e o r b i t s h o w s that C R E M E f a i l s to p r e d i c t a n e l e v a t e d l e v e l o f h i g h l a t i t u d e c o s m i c r a y s d u r i n g s o l a r m i n i m u m ( D y e r e t a l . 1999) . S i n c e M O S T i s s c h e d u l e d t o l a u n c h d u r i n g a n a c t i v e s o l a r p h a s e w h e n t h i s e l e v a t i o n i n c o s m i c r a y s i s n o t a n o b s e r v e d p h e n o m e n o n , C R E M E is s a t i s f a c t o r y f o r m o d e l i n g the M O S T r a d i a t i o n e n v i r o n m e n t . T h e S o l a r A n o m a l o u s a n d M a g n e t o s p h e r i c P a r t i c l e E x p l o r e r ( S A M P E X ) s a t e l l i t e h a s b r o u g h t t o l i g h t a n o v e r e s t i m a t i o n i n the C R E M E p r e d i c t i o n s o f t h e A C R ( T y l k a et a l , 1997) . T h e a c t u a l s p e c t r a d r o p o f f m u c h m o r e r a p i d l y at t h e h i g h e r e n e r g y e n d t h a n p r e d i c t e d b y the m o d e l s . S o e v e n t h o u g h the s i n g l y i o n i s e d p a r t i c l e s a r e m o r e p e n e t r a t i n g t h a n t h e i r h i g h e r c h a r g e d c o u n t e r p a r t s , t h e y h a v e r e l a t i v e l y l o w e n e r g i e s a n d a r e t h e r e f o r e m o r e e a s i l y a t t e n u a t e d b y s h i e l d i n g . T y l k a e s t i m a t e s that n o p a r t i c l e f r o m t h e A C R w i l l p e n e t r a t e 5 0 m i l s o f A l s h i e l d i n g . T h e u p d a t e to C R E M E g o e s as f a r as t o e x c l u d e t h e A C R as h a v i n g a n y e f f e c t o n m i c r o e l e c t r o n i c s . I n d e e d , t h e f l u x p r e s e n t e d b y A C R i n C h a p t e r 4 i s a n o r d e r o f m a g n i t u d e l e s s t h a n t h e G C R f l u x a n d t h u s , e v e n t h o u g h the m o d e l is a k n o w n o v e r e s t i m a t i o n , t h e u n c e r t a i n t y a s s o c i a t e d w i t h it i s n e g l i g i b l e c o m p a r e d to t h e u n c e r t a i n t y i n t h e t r a p p e d p r o t o n a n d e l e c t r o n m o d e l s . S i n c e t h e p r i m a r y c o m p o n e n t o f r a d i a t i o n i n the M O S T b a s e l i n e o r b i t i s m a d e u p o f t r a p p e d p r o t o n s a n d e l e c t r o n s i n the S A A , the u p d a t e d v e r s i o n o f C R E M E w a s n o t e m p l o y e d i n t h i s s t u d y . A l t h o u g h C R E M E 9 6 i s m o r e a c c u r a t e t h a n its p r e d e c e s s o r C R E M E , it is n o t i n t e g r a t e d i n t o S p a c e R a d i a t i o n 4 .0 . S i n c e the a c c u r a c y d i f f e r e n c e s are n e g l i g i b l e c o m p a r e d to the u n c e r t a i n t i e s i n t h e p r i m a r y p a r t i c l e p o p u l a t i o n , i t w a s n o t c o n s i d e r e d n e c e s s a r y to e v a l u a t e t h e G C R o r A C R w i t h g r e a t e r a c c u r a c y t h a n that a f f o r d e d b y C R E M E . 4 5 Chapter 4: Choosing a Baseline Orbit A s o u t l i n e d i n F i g u r e 3 . 1 , the s p a c e c r a f t e n g i n e e r m u s t s u p p l y a b a s e l i n e o r b i t t o b e e v a l u a t e d i n a r a d i a t i o n a n a l y s i s . C h o o s i n g a b a s e l i n e o r b i t c a n b e c o m p l i c a t e d as a n u m b e r o f f a c t o r s n o t r e l a t e d to the r a d i a t i o n e n v i r o n m e n t a r i s e . T h i s C h a p t e r i n v e s t i g a t e s s o m e e f f e c t s t h e M O S T m i c r o s a t e l l i t e w i l l f a c e i n t h e b a s e l i n e o r b i t e s t a b l i s h e d i n t h e f i r s t p h a s e o f m i s s i o n d e s i g n . 4.1 The MOST Baseline Orbit M O S T is b e s t s u i t e d to a l o w - E a r t h o r b i t ( L E O ) w h e r e t h e r a d i a t i o n e n v i r o n m e n t i s n o t h a r s h , s u c h as a l o w a l t i t u d e g e o - s y n c h r o n o u s o r b i t , o r a p o l a r o r b i t . T h e M O S T s c i e n c e t e a m c h o s e a p o l a r s u n - s y n c h r o n o u s o r b i t w i t h a n 8 0 0 k m a l t i t u d e b e c a u s e (a) it a l l o w s stars to r e m a i n i n s i g h t o f the t e l e s c o p e f o r a n e x t e n d e d p e r i o d o f t i m e ( S e c t i o n 4 .3 ) , (b) m i n i m i s e s s c a t t e r e d l i g h t c o n t r i b u t i o n s ( S e c t i o n 4 .6 ) , a n d (c ) it i s the b a s e l i n e o r b i t f o r R a d a r s a t 2 ( sa te l l i tes h i t c h i n g a r i d e to s p a c e can ' t b e t o o p i c k y a b o u t w h e r e t h e y e n d u p ) . T h e L o c a l T i m e o f A s c e n d i n g N o d e ( L T A N ) f o r t h e b a s e l i n e o r b i t i s 6 : 0 0 p . m . , s o that t h e sa te l l i te a l w a y s r e m a i n s a b o v e t h e t e r m i n a t o r o f t h e E a r t h . T h i s t y p e o f d a w n -d u s k o r b i t d e s c r i b e d f u r t h e r i n S e c t i o n 4 .5 i s a l s o f a v o r e d b y E a r t h m o n i t o r i n g m i s s i o n s as it p r o v i d e s g o o d r e l i e f i n i m a g e s . T h e a d v a n t a g e f o r M O S T is tha t it s i g n i f i c a n t l y r e d u c e s s c a t t e r e d l i g h t as a p h o t o m e t r i c n o i s e s o u r c e . O n e s i d e o f the sa te l l i te w i l l r e m a i n p o i n t e d i n t h e g e n e r a l d i r e c t i o n o f the s u n , c o n s t a n t l y s h i e l d i n g t h e o t h e r s i d e o f the sa te l l i te , w h i l e the t e l e s c o p e w i l l s tay p o i n t e d at a f i x e d s p o t i n t h e s k y i n t h e o p p o s i t e d i r e c t i o n o f the s u n . O v e r t h e c o u r s e o f a y e a r , t h e b e a m the t e l e s c o p e v i e w s o n t h e s k y s w e e p s o u t 3 6 0 ° i n R i g h t A s c e n s i o n , s o t h e c o n t i n u o u s v i e w i n g z o n e ( C V Z ) f o r the s a t e l l i t e i s a s t r i p a l o n g t h e c e l e s t i a l e q u a t o r . T h e g r o u n d t r a c k s s p a n t h e w h o l e E a r t h , s o t h e r e is s u f f i c i e n t c o m m u n i c a t i o n t i m e w i t h p l a n n e d g r o u n d s t a t i o n s i n V a n c o u v e r a n d T o r o n t o ( C a n a d a ) a n d V i e n n a ( A u s t r i a ) . H o w e v e r , t h e sa te l l i te w i l l g r a z e t h e V a n A l l e n r a d i a t i o n b e l t s i n t h e S A A d u r i n g 1 8 % o f t h e o r b i t a l p a s s e s . 4 6 Figure 4.1 Data from the F U S E guide camera comparing regions (a) outside the S A A , and (b) inside the S A A . Over-plotted is the M O S T 'donut' shaped pupil image drawn to scale. Each pixel that is dark in the second frame is a lit pixel , and the lines are tracks where charged particles have hit with a high grazing angle and thus penetrated across many pixels in the direction o f their path through the device. (Courtesy o f T i m Hardy, D A O . ) 4.2 Cosmic Ray hits A l t h o u g h a l s o c a u s e d b y h i g h - e n e r g y p a r t i c l e s i n L E O , c o s m i c r a y hi ts d o n o t p e r m a n e n t l y d a m a g e a n y o n b o a r d s p a c e c o m p o n e n t s . W h e n a n e n e r g e t i c c h a r g e d p a r t i c l e f r o m a n y o f t h e f o u r p o p u l a t i o n s o f p a r t i c l e s d e s c r i b e d i n S e c t i o n 2.4 h i t s the C C D , it c a n i o n i s e o n e o f t h e S i a t o m s , r e l e a s i n g a n e l e c t r o n a n d l e a v i n g a n e l e c t r o n h o l e p a i r . T h e e l e c t r o n s are c o l l e c t e d b y t h e e l e c t r i c f i e l d s o f the d e v i c e a n d i n c o r p o r a t e d as s i g n a l . T h u s , p i x e l s h i t b y a n i n c o m i n g p a r t i c l e b e c o m e " l i t " w i t h a b n o r m a l l y h i g h s i g n a l c o m p a r e d t o t h e b a c k g r o u n d s i g n a l . T h e F a r U l t r a - V i o l e t S p e c t r o s c o p i c E x p l o r e r ( F U S E ) i s o r b i t i n g t h e E a r t h c u r r e n t l y , s e n d i n g d a t a t a k e n f r o m b o t h i n s i d e the S A A a n d f r o m t h e q u i e s c e n t r e g i o n s o u t s i d e the S A A . F i g u r e 4 . 1 , t w o d a t a f r a m e s f r o m t h e F U S E F i n e E r r o r S e n s o r ( F E S ) w h i c h u s e s a C C D d e t e c t o r , i l l u s t r a t e s t h e n u m b e r o f l i t p i x e l s d u e t o c r o s s i n g the S A A . T h e s p u r i o u s s i g n a l s c r e a t e d b y c o s m i c r a y h i t s i n s i d e t h e S A A w i l l b e t r e a t e d d u r i n g d a t a r e d u c t i o n . T h e m a j o r i t y o f the r a d i a t i o n f l u x is c e n t r a l i s e d i n the S A A , b u t c h a r g e d p a r t i c l e s w i l l s t i l l h i t t h e d e t e c t o r o u t s i d e t h i s r e g i o n at a m u c h l o w e r rate. T h u s , 4 7 the d a t a r e d u c t i o n s c h e m e e m p l o y e d b y M O S T m u s t c o n s i d e r r e m o v i n g ' l i t ' p i x e l s d u e to c o s m i c r a y h i t s , o r t o l e r a t i n g t h e m . T h e r e are t w o o p t i o n s f o r c o s m i c r a y r e m o v a l , b o t h e m p l o y e d b y g r o u n d b a s e d a s t r o n o m e r s : (a) r e m o v e t h e p i x e l c o m p l e t e l y f r o m the d a t a set, o r b ) a s s i g n a v a l u e t o t h e l i t p i x e l that i s a n a v e r a g e o f t h e s u r r o u n d i n g p i x e l s . S i n c e c o s m i c r a y h i t s o c c u r o v e r a v e r y s h o r t t i m e s c a l e , t h e y c a n b e u n a m b i g u o u s l y d e t e c t e d i f t h e s i g n a l f r o m a l i t p i x e l i s h i g h o n e i n t e g r a t i o n , a n d t h e n a r e a s o n a b l e v a l u e i n t h e n e x t s e q u e n t i a l i n t e g r a t i o n . 4.3 The Continuous Viewing Zone (CVZ) T h e M O S T o r b i t i s d e s i g n e d s u c h that t h e o p t i c a l a x i s o f t h e t e l e s c o p e is s t e e r a b l e w i t h i n a c o n e c e n t e r e d i n t h e a n t i - s o l a r d i r e c t i o n w i t h a d i a m e t e r o f 2 7 . 3 ° (set b y the o r b i t , F i g u r e 4 .2 ) . A s t h e E a r t h r e v o l v e s a r o u n d t h e s u n , t h i s p r o j e c t i o n w i l l s w e e p o u t a p a t h a l o n g t h e s k y , m u c h l i k e t h e MOST, s e a r c h l i g h t o f a l i g h t h o u s e b e a m . A s the b e a m s w e e p s a c r o s s t h e s k y , the m i c r o s a t e l l i t e w i l l p o i n t at s te l lar targets w h i c h f a l l i n s i d e its a rea . D e p e n d i n g o n t h e l o c a t i o n o f t h e star i n s i d e t h e C V Z , i f it t r a n s v e r s e s t h e C V Z at a h i g h e r p o i n t t h a n at the e q u a t o r o f the p r o j e c t i o n , it w i l l h a v e a s h o r t e r d w e l l t i m e i n the C V Z . F o r e x a m p l e , P r o c y o n is v i s i b l e i n t h e C V Z f o r 7 .9 w e e k s , w h e r e a s G a m L e o A is o n l y v i s i b l e f o r 4 . 2 w e e k s . S e e A p p e n d i x C f o r t h e d w e l l t i m e o f t h e M O S T p r i m a r y targets as a f u n c t i o n o f o r b i t a l p a r a m e t e r s . T h e d i a m e t e r o f t h e C V Z is a f u n c t i o n o f o r b i t a l i n c l i n a t i o n a n d a l t i t u d e . I f M O S T i s p u t i n t o a h i g h e r a l t i t u d e o r b i t , the d i a m e t e r o f the C V Z w i l l i n c r e a s e as t h e l i m i t i n g F i g u r e 4.2 Schematic of the MOST baseline orbit showing Continuous Viewing Zone (CVZ), Orbit Normal Vector (ONV), Inclination angle (/), and Beta Angle (p). boundary of the cone created by the limb of the Earth is at a larger angle. Figure 4.3 shows the MOST targets on the sky with the limits of the MOST CVZ for different inclinations also projected. A higher inclination, higher altitude orbit favours more targets. 49 60 4 0 s  20 a u XI c 0 c J_11 • 11 III I I I I I M I I Illllllll Illllllll Illllllll Illllllll im in II Illllllll Illllllll Illllllll Illllllll 111 m i l l eVZ bou «fc»y. 98 6. 799.4 CVZ bow 8, 603.2 km -Mill B* a oGem A Her ft 1 • it Peg ~ Illllllll F?30ri Or 10 • Pre Tn cyon ^ m L e o A t Et o E*sV" 3 B 0 0 1 CS BelHer .mSer Itc a*. BetOel ^ V l p E l III 1 - a 9K tVift GamVlr 1 1 1 1 1 1 1 <TT3 -' „ RT10 Sqr Illllllll I Illllllll i II i I l l l l l l l l I I I I I I I I I IIIIIIIII IIIIIIIII I I I I I I I I I I l l l l l l l l I l l l l l l l l II II 1 1 I (1 I l l l l l l l l IIIIIIIII I I I I I I I I I 5 - 2 0 -40 b) 0 30 60 9 0 1 2 0 150 180 2 1 0 2 4 0 2 7 0 3 0 0 3 3 0 3 6 0 R i g h t A s c e n s i o n ( d e g r e e s ) :l III111II IIIIIIIII IIIIIIIII I I I I I I I I I III I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I TT11111 II I l l l l l l l l 111 II 1 M l p Z boui idoiy, 9 8 6, 799.4 Um -eVZ boui doiy, 9 7 8. 603.2 Um -E 2 4 9 3 0 1 1 1 1 1 Illllllll HQ 178 232 # t28onnE a c Illllllll -Hi 11217 wk 1: f& 113 '3 1 1 1 1 1 1 1 13 Illllllll: z H i I I I I I I I I I i n I I I I I I I I I IIIIIIIII I I I I I I I I I I I I I I I I I I 1 1 " 1 1 1 I I I I I I I I I 1111 : i 1 1 60 4 0 2 0 U ~Q c o "5 c O - 2 0 - 4 0 0 30 6 0 9 0 120 150 180 2 1 0 2 4 0 2 7 0 3 0 0 3 3 0 3 6 0 R i g h t A s c e n s i o n ( d e g r e e s ) Figure 4.3 MOST targets and limits of CVZ as a function of orbital inclination/altitude projected on the sky for a) the expanded MOST solar type targets, and b) other targets. 5 0 4.4 The MOST Duty Cycle T h e d u t y c y c l e i s d e f i n e d as the a m o u n t o f t i m e that a t e l e s c o p e c a n c o n t i n u a l l y s tare at a s t e l l a r o b j e c t . I n o r d e r to p e r f o r m a s t e r o s e i s m o l o g y s u c c e s s f u l l y , a v e r y h i g h d u t y c y c l e i s e s s e n t i a l . I n f a c t , a l i m i t e d d u t y c y c l e is o n e o f t h e s t r o n g l i m i t a t i o n s o f p e r f o r m i n g a s t e r o s e i s m o l o g y f r o m t h e g r o u n d . C o n s o r t i u m s h a v e f o r m e d i n a n a t t e m p t to n e t w o r k t e l e s c o p e s a l l o v e r the E a r t h i n t o a s i m u l t a n e o u s o b s e r v i n g c a m p a i g n c a l l e d the W h o l e E a r t h T e l e s c o p e , W E T . T h e C V Z is d e s i g n e d to a l l o w o b j e c t s to f a l l i n t o t h e b o r e s i g h t s o f t h e M O S T m i c r o s a t e l l i t e f o r a n e x t e n d e d , uninterrupted p e r i o d o f t i m e . I n a s t e r o s e i s m i c d a t a a n a l y s i s , F o u r i e r t i m e s e q u e n c e a n a l y s i s i s p e r f o r m e d . It i s a p o w e r f u l m e t h o d o f d e t e c t i n g r e g u l a r i t i e s i n t h e s i g n a l f r o m t h e star. H o w e v e r , it i s a l s o a v e r y p o w e r f u l w a y o f d e t e c t i n g a n y t h i n g e l s e i n the d a t a set w h i c h h a s a r e p e t i t i v e p a t t e r n , s u c h as r e g u l a r g a p s o f d a t a . I n a p e r f e c t w o r l d , w h e r e t h e p h o t o m e t r i c t i m e s e r i e s is c o m p l e t e , the F o u r i e r a n a l y s i s o f a s i n g l e f r e q u e n c y w o u l d r e t u r n t h e s i n g l e f r e q u e n c y a l o n e . H o w e v e r , f o r a r e d u c t i o n o f the d u t y c y c l e o f 1 0 % , s i d e - l o b e s to t h e p r i m a r y s i g n a l are c r e a t e d , as i l l u s t r a t e d b y F i g u r e 4 .4 . T h e s e s i d e l o b e s are a l i a s e s o r g h o s t s i g n a l s o f t h e p r i m a r y f r e q u e n c y . F o r c o m p a r i s o n , t h e s p e c t r a l w i n d o w f r o m a s i n g l e - g r o u n d b a s e d s i g h t i s a l s o p r e s e n t e d . It i s c l e a r that the s i g n a l d u e to a n o s c i l l a t i n g star i s a c h a l l e n g e to e x t r a c t f r o m a g r o u n d b a s e d d a t a set. W h i l e M O S T p a s s e s t h r o u g h the S A A , the n u m b e r o f c o s m i c r a y h i t s a n d p r o t o n i n d u c e d S E E s w i l l b e h i g h , a n d p o s s i b l y t o o h i g h t o a l l o w o n e t o u t i l i s e d a t a t a k e n d u r i n g t h e p a s s a g e . T h u s , t h e r e m a y b e s m a l l g a p s i n the M O S T d a t a set c o r r e s p o n d i n g to t i m e s w h e n M O S T is i n t h e S A A . I n a w o r s t - c a s e s c e n a r i o w i t h n o s h i e l d i n g at a l l , M O S T w o u l d l o o s e d a t a f r o m the i m m e d i a t e b o u n d a r i e s o f the S A A . T h u s , the d u t y c y c l e w o u l d b e a b o u t 8 2 % c o m p l e t e ( that i s , M O S T w o u l d l o s e 1 8 % o f its d a t a d u e t o the S A A ) . M o r e r e a l i s t i c a l l y , M O S T w i l l s t i l l b e a b l e to t a k e g o o d d a t a t h r o u g h o u t t h e S A A w h e r e p a r t i c l e f l u x i s r e l a t i v e l y l o w . S i n c e the p u p i l i m a g e f o r the s c i e n c e d a t a set o n l y - 6 4 0 0 p i x e l s , t h e a c t u a l n u m b e r o f l i t p i x e l s e x p e c t e d i n the s c i e n c e d a t a i n t h e d e n s e s t par t o f t h e S A A is n o t e x p e c t e d to b e s i g n i f i c a n t . T h e l i m i t i n g f a c t o r to a c c u m u l a t i n g d a t a t h r o u g h t h e S A A m a y b e t h e a t t i tude c o n t r o l s y s t e m ( A C S ) p e r f o r m a n c e , a l t h o u g h w i t h a p p r o p r i a t e t h r e s h o l d i n g , the a l g o r i t h m f o r g u i d i n g s h o u l d b e s u f f i c i e n t to a l l o w g u i d i n g 51 t h r o u g h t h e S A A . T h u s , a 9 0 % d u t y c y c l e i s the m i n i m u m e x p e c t e d . S i m u l a t i o n s o f t h e p h o t o m e t r i c p e r f o r m a n c e o f M O S T w i t h a n 8 0 % d u t y c y c l e b y K u s c h n i g h a v e s h o w n that the p h o t o m e t r i c p r e c i s i o n r e q u i r e m e n t s c a n s t i l l b e m e t ( K u s c h n i g et a l . 1999) . duty cycle = 100 % duty cycle - 90 % MOST Orbit -with shielding I duty cycle = 80 % MOST Orbit -without shielding I duty cycle = 35 % f requency [ m H z l Figure 4.4 The spectral window for the MOST microsatellite, based on the approximate SAA location shown in the top inset, (a) shows an ideal spectral window for a complete data set, (b) for a duty cycle with a loss of 10% in completeness due to passages through the S A A (c) for a duty cycle 20% incomplete, and (d) for a typical ground based sight that can only observe during the night (Courtesy of Kuschnig, 2000). 53 4.5 Eclipse Season T h e b a s e l i n e o r b i t h a s a L o c a l T i m e o f A s c e n d i n g N o d e ( L T A N , t h e t i m e at w h i c h t h e sa te l l i te c r o s s e s f r o m t h e S o u t h e r n H e m i s p h e r e o f t h e E a r t h t o the N o r t h e r n ) o f 6 p . m . T h u s , t h e sa te l l i te w i l l a l w a y s r e m a i n a b o v e the t e r m i n a t o r o f t h e E a r t h ( w h e r e t h e s u n l i t p o r t i o n o f t h e E a r t h m e e t s t h e d a r k p o r t i o n ) ( F i g u r e 4 .2 ) . M O S T w i l l p e e r o u t o v e r t h e d a r k l i m b o f the E a r t h f o r the m a j o r i t y o f t h e o r b i t . T h i s i s e q u i v a l e n t to a n o r b i t w i t h L T A N o f 6 a . m . , e x c e p t t h e sa te l l i te c r o s s e s f r o m t h e S o u t h e r n to N o r t h e r n h e m i s p h e r e at d a w n as o p p o s e d to d u s k . T h u s , t h e s e o r b i t s are r e f e r r e d to as d a w n - d u s k o r b i t s . D u r i n g w i n t e r a n d s u m m e r e c l i p s e s e a s o n s w h e n the S u n is at its m o s t e x t r e m e i n c l i n a t i o n r e l a t i v e t o t h e E a r t h ' s e q u a t o r , t h e p l a n e o f M O S T ' s o r b i t w i l l b e the f u r t h e s t f r o m t h e t e r m i n a t o r ( w h e t h e r it i s i n a d a w n o r a d u s k o r b i t ) . F o r a m a x i m u m o f 17 m i n u t e s ( 1 7 % o f the o r b i t , i n c l u d i n g u m b r a l a n d p e n u m b r a l p o r t i o n s o f the e c l i p s e ) at the s u m m e r s o l s t i c e M O S T w i l l b e e c l i p s e d b y t h e E a r t h , c u t t i n g o f f d i r e c t p o w e r s u p p l y f r o m M O S T ' s s o l a r a r r a y s a n d f o r c i n g t h e sa te l l i te t o r e l y o n its b a t t e r i e s . A d d i t i o n a l l y , m a n y s a t e l l i t e s are v e r y s e n s i t i v e to t e m p e r a t u r e g r a d i e n t s . A s t h e y a r e s h a d o w e d f r o m t h e s u n a n d t h e t e m p e r a t u r e d r o p s , t h e y m a y e x p e r i e n c e " t h e r m a l s n a p " , a f l e x u r e o f the m e c h a n i c a l s t ruc ture . S i n c e M O S T is s o s m a l l , t h e r m a l f l e x u r e s h o u l d n o t b e s i g n i f i c a n t . H o w e v e r , the a t t i tude c o n t r o l s y s t e m w i l l b e m o r e s e n s i t i v e to t h i s p h e n o m e n o n as o p t i c a l f o c u s m a y b e c o m e s l i g h t l y d i s t o r t e d . F i g u r e 4 .5 s h o w s t h e d u r a t i o n o f i n d i v i d u a l e c l i p s e s f o r the M O S T b a s e l i n e o r b i t f r o m O c t o b e r 2 0 0 1 t h r o u g h J a n u a r y 2 0 0 4 . S i n c e p o w e r i s r e d u c e d , M O S T m a y n o t b e a b l e to f u n c t i o n i n n o r m a l o p e r a t i n g m o d e . E c l i p s e s e a s o n w o u l d b e m o s t a p p r o p r i a t e l y s p e n t p e r f o r m i n g t e s t i n g a n d e n g i n e e r i n g o p e r a t i o n s . 5 4 Lunar eclipses, also shown in Figure 4 . 5 have moderate to long duration. However, since there is not very many consecutive eclipses (repeated over many orbits) relative to the number of consecutive eclipses during the eclipse season, power levels should not be significantly affected. Eclipse Duration, 800km altitude, 6pm LTAN 1200 1000 800 600 2 3 Q © <2 400 200 Umbral eclipses The eclipse season in the baseline orbit lasts from May 17 to July 27 Penumbral ecl ipses 21-Oct-02 10-Dec-02 29-Jan-03 20-Mar-03 09-May-03 28-Jun-03 Date 17-Aug-03 06-Oct-03 25-Nov-03 14-Jan-04 Figure 4.5 Eclipse duration for the MOST baseline orbit. The central, darkest region of the eclipse is the umbra, while the penumbra is the less shadowed outer portion of the eclipse. Eclipses outside the eclipse season are caused by the moon's shadow. The L T A N of the orbit determines when the eclipse season will occur. As shown in Figure 4 . 5 , for a L T A N of 6 p.m., the eclipse season is centered on the summer solstice. For a L T A N of 6 am, the eclipse season is offset by 6 months to be centered around the winter solstice. A noon/midnight orbit would have its eclipse season at the vernal or spring equinox. 55 4.6 Stray Light Effects A t t h e o p p o s i t e p o i n t o f the o r b i t w h e r e M O S T i s e c l i p s e d f r o m the S u n b y the E a r t h , M O S T w i l l b e f o r c e d to p e e r o u t o v e r t h e s u n l i t l i m b o f t h e E a r t h a n d s c a t t e r e d l i g h t s i g n a l w i l l i n c r e a s e . E x p e r i e n c e f r o m t h e s t a r - s e n s o r a b o a r d t h e f a i l e d W I R E m i s s i o n , a l s o i n a p o l a r s u n - s y n c h r o n o u s o r b i t ( i n c l i n a t i o n 9 7 ° , a l t i t u d e 4 7 0 x 5 4 0 k m ) , s h o w s that the c o n t r i b u t i o n o f s i g n a l f r o m p e e r i n g o v e r t h e b r i g h t l i m b o f t h e E a r t h i s s u b s t a n t i a l . F i g u r e 4 . 6 s h o w s a b r i e f s e q u e n c e o f d a t a t a k e n b y W I R E w i t h a g a p d u e t o o c c u l t a t i o n b y the E a r t h . T h e i n c r e a s e i n i n t e g r a t e d s i g n a l i m m e d i a t e l y b e f o r e t h e o c c u l t a t i o n c o r r e s p o n d s d i r e c t l y to the t i m e w h e n t h e s t a r - s e n s o r o b s e r v e s o v e r the s u n - l i t l i m b o f t h e E a r t h . D a t a p r o c e s s i n g p r o c e d u r e s u s e d b y B u s a z i i n a n a t t e m p t to d e t e c t o s c i l l a t i o n s i n t h e A l t a i r 7.0x10-1 6.8x10* H Q 6.6x10' V 6.4x1 ( M ^ 6.2x10* H 6.0x10'' X C O E 5.8x10* H CO — 5.6x10* H CO C .2> 5.4x10* H CO 5.2x10* H 5.0x10* WIRE Startracker - Altair field - Star 2 Observation: 18 October 1999 i 1470.20 SAA Target Star occulted by earth 1470.22 1470.24 1 1470.26 Time (seconds) — i — 1470.28 1470.30 Figure 4.6 Light curve taken by the star-sensor onboard the WIRE satellite showing a dramatic increase in signal prior to occultation by the Earth when the satellite peers out over the bright limb of the Earth. (Figure courtesy of Kuschnig, Data courtesy of Busazi.) 5 6 . RAAN;Oh (dawn Dusk) Lower edge of CVZ l i g h t c u r v e d i s c a r d s a n y d a t a t a k e n p r i o r to a n o c c u l t a t i o n ( K u s c h n i g , p e r s o n a l c o m m u n i c a t i o n ) . O r b i t s w i t h v a r y i n g L T A N s h a v e b e e n c o n s i d e r e d , e s p e c i a l l y s i n c e n o t e v e r y sa te l l i te m a k e s it i n t o t h e i r o p t i m u m o r b i t u p o n l a u n c h . I n c r e a s i n g the L T A N f r o m d a w n / d u s k to n o o n / m i d n i g h t c a u s e s t h e sa te l l i te o r b i t the E a r t h a l o n g a f i x e d p l a n e r e l a t i v e to t h e E a r t h s e p a r a t e d b y a l a r g e r a n g l e 9 f r o m t h e p l a n e o f t h e t e r m i n a t o r ( F i g u r e 4.7). I n o r b i t s w i t h L T A N a p p r o a c h i n g n o o n o r m i d n i g h t , t h e p h o t o m e t r i c n o i s e d u e t o s c a t t e r e d l i g h t f r o m t h e E a r t h i n c r e a s e s d r a m a t i c a l l y . A c o m p l i c a t i n g f a c t o r i n e s t i m a t i n g t h e a m o u n t o f s c a t t e r e d l i g h t f r o m t h e l i m b o f t h e E a r t h i s t h e a l b e d o o f t h e E a r t h i s n o t c o n s t a n t . H e n c e , M O S T s h o u l d b e i n a n o r b i t w h e r e 9 i s l ess t h a n 9 m a x ( the a n g l e b e t w e e n t h e i n t e r s e c t i o n p o i n t o f the l o w e r m o s t b o r e - s i g h t o f the C V Z a n d t h e o r b i t a l p l a n e ) i n o r d e r to r e d u c e s c a t t e r e d l i g h t c o n t r i b u t i o n s . G r a n t e d , m a n y o f M O S T ' s t a r g e t s d o n o t f a l l d i r e c t l y a l o n g t h i s l o w e r b o r e - s i g h t ( F i g u r e 4 .3). B u t s i n c e s u n l i g h t i s d i r e c t e d o u t w a r d s a n d w i l l r e f l e c t o f f t h e a t m o s p h e r e o r i n t e r p l a n e t a r y p a r t i c l e s b a c k t o w a r d s t h e t e l e s c o p e , a c o n s e r v a t i v e o b s e r v a t i o n w o u l d o n l y b e m a d e i n the u p p e r h a l f o f the C V Z f o r s u c h a n o r b i t . F i g u r e 4.8 s h o w s 9 f o r t h r e e d i f f e r i n g o r b i t s , f r o m t h e b a s e l i n e d a w n - d u s k o r b i t t h r o u g h to a n o r b i t w i t h L T A N 7 p . m . . 8 p . m . , a n d L T A N 9 p . m . E v e n f o r a d a w n - d u s k o r b i t , 9 e x c e e d s 9 m ax i n t h e s u m m e r s e a s o n ( e c l i p s e s e a s o n ) . T h e a m o u n t o f t i m e d u r i n g When 0 is greater than 6 then the MOST boresight will be facing directly over the bright limb of the earth. Figure 4.7 Schematic of MOST orbiting the Earth viewed looking down on the North Pole. Changing the LTAN of the orbit causes MOST to peer out over the sunlit limb of the Earth, increasing photometric noise due to scattered light. Note that Right Ascension of Ascending Node (RAAN) is the same as LTAN measured in degrees of right ascension as opposed to local time. 5 7 the y e a r that t h e sa te l l i te w i l l s tare o u t o v e r a s u n l i t l i m b o f the e a r t h i s v e r y s e n s i t i v e to t h e L T A N . I f t h e L T A N is la ter t h a n 8 p . m . ( o r c o n v e r s e l y e a r l i e r t h a n 4 p . m . ) t h e n t h e s a t e l l i t e w i l l a l w a y s stare o u t o v e r t h e b r i g h t p o r t i o n o f the e a r t h . I n a l l n o n d a w n - d u s k o r b i t s , M O S T w i l l n e e d g r e a t e r p o w e r s u p p l i e s t h a n are c u r r e n t l y b u d g e t e d . T h u s , it i s i m p e r a t i v e that M O S T g o i n t o a d a w n - d u s k p o l a r o r b i t ( L T A N e i t h e r 6 a . m . o r 6 p . m . ) . 60 L T A N : 9 p.m. o l-Oct-02 20-Nov-02 9-Jan-03 28-Feb-03 19-Apr-03 Date 8-Jun-03 28-M-03 16-Sep-03 Figure 4.8 0 as a function of LTAN over the course of a year for the MOST baseline orbit (800 km). The amount of time that 0 exceeds 0 ^ increases greatly as the orbit deviates from a dawn dusk orbit. H e l i o s y n c h r o n o u s o r b i t s are s t a b l e o v e r a r a n g e o f a l t i t u d e s w h e r e the i n c l i n a t i o n o f a h e l i o s y n c h r o n o u s o r b i t is a f u n c t i o n o f the a l t i t u d e ( S e e A p p e n d i x B f o r i n c l i n a t i o n v s . a l t i t u d e o f h e l i o s y n c h r o n o u s o r b i t s ) . 0 is n o t s t r o n g l y d e p e n d e n t o n a l t i t u d e o f the o r b i t s i n c e i n c l i n a t i o n o n l y c h a n g e s s l i g h t l y as a f u n c t i o n o f a l t i t u d e . H o w e v e r , 0 m a x d o e s c h a n g e s i g n i f i c a n t l y w i t h a l t i t u d e ( G m a x is 2 3 . 9 3 ° , 2 7 . 3 1 ° , a n d 3 0 . 1 8 ° at 6 0 0 k m , 8 0 0 k m , a n d 1 0 0 0 k m r e s p e c t i v e l y ) . F i g u r e 4 . 9 s h o w s the m a x i m u m a l l o w a b l e v a l u e o f t h e L T A N ( d e f i n e d as 0 > 0 , ^ ) f o r a 6 0 0 k m , 8 0 0 k m , a n d 1000 k m s u n - s y n c h r o n o u s o r b i t o n 58 J a n u a r y 1,2002. S i n c e 0 c h a n g e s w i t h t h e s e a s o n s , t h e s e m a x i m u m a l l o w a b l e L T A N s w i l l b e c l o s e r to n o o n / m i d n i g h t o v e r s p r i n g a n d f a l l e q u i n o x e s a n d d a w n / d u s k d u r i n g w i n t e r a n d s u m m e r s o l s t i c e s . A s p e r F i g u r e 4.9, e v e n i n a d a w n - d u s k o r b i t , t h e r e i s a s e a s o n i n w h i c h 0 e x c e e d s 0 m a x . 10 6 6.5 7 7.5 . 8 8.5 9 Local Time of Ascending Node (hours p.m.) Figure 4.9 Maximum allowable values of the LTAN for heliosynchronous orbits with 600 (short dash) 800 (solid), and 1000 km (long dash) altitude on January 1, 2002. 59 Chapter 5: The Weather Forecast for the MOST microsatellite N o w that a b a s e l i n e o r b i t is e s t a b l i s h e d a n d it i s c l e a r that t h e o r b i t a l e n v i r o n m e n t o u t s i d e o f t h e r a d i a t i o n e n v i r o n m e n t is t o l e r a b l e w i t h i n M O S T m i s s i o n p a r a m e t e r s , it is e s s e n t i a l to d e t e r m i n e the r a d i a t i o n e n v i r o n m e n t o f the o r b i t t o e n s u r e t h e s a t e l l i t e d e s i g n c a n t o l e r a t e its i m p a c t . T h i s c h a p t e r o u t l i n e s the steps u s e d to e s t a b l i s h t h e r a d i a t i o n e n v i r o n m e n t f o r the M O S T m i c r o s a t e l l i t e b a s e d o n the a p p r o a c h d e t a i l e d i n C h a p t e r 3. 5.1 The geomagnetic field A s p e r F i g u r e 3 . 1 , t h e n e x t s tep i n e v a l u a t i n g t h e r a d i a t i o n e n v i r o n m e n t o f t h e M O S T m i c r o s a t e l l i t e i s to c a l c u l a t e the g e o m a g n e t i c f i e l d ( S e c t i o n 3 .1 .2 ) t o b e u s e d i n A P 8 a n d A E 8 . F i g u r e 5.1 s h o w s g e o m a g n e t i c field s t r e n g t h f o r the M O S T m i c r o s a t e l l i t e b a s e l i n e o r b i t b a s e d o n t h e I G R F 2 0 0 0 field e x t r a p o l a t e d to a f l i g h t e p o c h o f 2 0 0 2 . D u e to the s u g g e s t i o n that o n l y the J e n s e n a n d C a i n m o d e l s s h o u l d b e u s e d w i t h Longitude Figure 5.1 Magnetic field strength for the MOST baseline orbit (flight epoch 2002) clearly showing the depression in magnetic field strength associated with the SAA (Section 2.3.1). 6 0 A P 8 a n d A E 8 ( S e c t i o n 3 .3 ) , o t h e r g e o m a g n e t i c f i e l d m o d e l s w e r e a p p l i e d to see i f a n y n o t i c e a b l e d i f f e r e n c e i n p r o t o n o r e l e c t r o n f l u x r e s u l t e d . M o d e l s c o m p a r i n g t h e p r o t o n e n v i r o n m e n t s u s i n g G S F C - 1 2 / 6 6 a n d t h e I n t e r n a t i o n a l G e o m a g n e t i c R e f e r e n c e F i e l d ( I G R F , see S e c t i o n 2 .3) s h o w e d n e a r l y i d e n t i c a l s o l a r m a x t r a p p e d p r o t o n s p e c t r a ( F i g u r e 5 .2) . H e n c e , f o r s o l a r m a x i m u m , the u p d a t e d g e o m a g n e t i c f i e l d m o d e l s w e r e e m p l o y e d as r e c o m m e n d e d f r o m t h e a u t h o r s o f S P A C E R A D I A T I O N 4 .0 . T h e J e n s e n a n d C a i n s o l a r m i n i m u m m o d e l J C 6 0 w a s n o t a c c e s s i b l e w i t h the S p a c e R a d i a t i o n p a c k a g e a n d h e n c e , v a r i a t i o n s d u e to the c h o i c e o f m a g n e t i c f i e l d m o d e l d u r i n g s o l a r m i n i m u m w e r e n o t i n v e s t i g a t e d . A d d i t i o n a l l y , I G R F 2 0 0 0 w a s i m p o r t e d i n t o S p a c e R a d i a t i o n . I G R F 2 0 0 0 , t h e m o s t r e c e n t l y p u b l i s h e d o f t h e r e f e r e n c e f i e l d m o d e l s , c o n t a i n s t i m e d e r i v a t e s o f t h e m a g n e t i c f i e l d s o that s e c u l a r v a r i a t i o n s c a n b e i n c l u d e d a n d the field c a n b e e x p t r a p o l a t e d to t h e M O S T f l i g h t e p o c h o f 2 0 0 2 . T h u s , it is t h e m o s t c u r r e n t r e p r e s e n t a t i o n o f the E a r t h ' s m a g n e t i c f i e l d a n d t h e m o s t r e a l i s t i c to u s e i n m o d e l l i n g . H e n c e , t h e I G R F s u p p l i e d a n d r e c o m m e n d e d b y t h e S p a c e R a d i a t i o n s o f t w a r e p a c k a g e w e r e u s e d a n d c o m p a r e d to the n e w l y p u b l i s h e d I G R F 2 0 0 0 . A l t h o u g h t h e m o d e l c o e f f i c i e n t s h a v e c h a n g e d b e t w e e n e p o c h s , t h e o v e r a l s t r e n g t h o f t h e i n n e r m a g n e t i c f i e l d h a s r e m a i n e d c o n s t a n t . T h u s , t r a p p e d p r o t o n s p e c t r a are i d e n t i c a l f o r t h e n e w e r a n d o l d e r v e r s i o n s o f I G R F . H o w e v e r , s c a l i n g I G R F t o t h e e p o c h o f f l i g h t e x p e c t e d f o r the M O S T m i c r o s a t e l l i t e ( 2 0 0 2 ) s h o w s a m i n o r i n c r e a s e i n t r a p p e d p r o t o n s p e c t r a , r e l a t e d to the e x p e c t e d i n c r e a s e i n s o l a r p r o t o n s i n j e c t e d f r o m t h e c u r r e n t p h a s e o f s o l a r m a x i m u m (see F i g u r e 4 .10 ) . D y e r et a l . ( 1 9 9 8 ) n o t e that d e s p i t e the r e c o m m e n d a t i o n s a g a i n s t u s i n g u p d a t e d f i e l d m o d e l s , u s i n g t h e n e w e r f i e l d m o d e l s d i d p r e d i c t the c o r r e c t n u m b e r o f p a s s e s o f t h e S T S - 8 1 m i s s i o n t h r o u g h t h e S A A . H o w e v e r , t h e d e f i n i t i v e b o u n d a r i e s o f the a r e s t i l l n o n - s t a t i c a n d m a y r e q u i r e r e - e v a l u a t i o n p r i o r to t h e l a u n c h o f the M O S T m i s s i o n . 61 l.OOE+15 1.00E+14 g l.OOE+13 2 1.00E+12 l.OOE+11 10 Energy (MeV) Trapped Proton Fluences AP8MAX — I G R F ...GSFC-12/66 . . IGRF2002 1000 Figure 5.2 Trapped proton spectra for AP8MAX used with three different magnetic field models: IGRF, GSFC-12/66, and IGRF extrapolated to the MOST flight epoch of 2002. There is no noticeable difference between IGRF and GSFC-12/66. However, the flight epoch spectrum has slightly higher proton fluence due to solar modulation of the trapped proton population. T h e F a r U l t r a - V i o l e t S p e c t r o s c o p i c E x p l o r e r ( F U S E ) s a t e l l i t e , a n i n t e r n a t i o n a l l y f u n d e d s p a c e sate l l i te e x p l o r e r i n g t h e u l t r a - v i o l e t u n i v e r s e , s p e n t e x t e n s i v e t i m e m a p p i n g o u t the b o u n d a r i e s o f t h e S A A d u r i n g the first y e a r o f its m i s s i o n ( A l e x F u l l e r t o n , p e r s o n a l c o m m u n i c a t i o n 2000). H e n c e , M O S T s h o u l d t a k e a d v a n t a g e o f t h e i r e x p e r i e n c e a n d u t i l i s e t h e m a p g e n e r a t e d b y t h e i r t e a m to p r e d i c t w h e n t h e s a t e l l i t e w i l l e n t e r the S A A to r e j e c t d a t a w h i c h m a y b e c o r r u p t e d d u e to c o s m i c r a y hi ts o r m a l f u n c t i o n o f the A t t i t u d e C o n t r o l S y s t e m ( A C S ) . D a t a t a k e n d u r i n g t h e p a s s a g e t h r o u g h t h e S A A c o u l d b e a n a l y s e d a n d c o m p a r e d w i t h the p r e d i c t i o n s f r o m t h i s s t u d y to f u r t h e r e v a l u a t e the v a l i d i t y o f t h e m o d e l s . 62 5.2 Geomagnetic Shielding M O S T w i l l o r b i t at a r e l a t i v e l y l o w a l t i t u d e , w h e r e t h e g e o m a g n e t o s p h e r e w i l l s h i e l d the sa te l l i te f r o m m u c h i n t e r p l a n e t a r y r a d i a t i o n . T h e g e o m a g n e t i c t r a n s m i s s i o n f u n c t i o n ( S e c t i o n 3.3), w i t h a n d w i t h o u t the E a r t h ' s s h a d o w , f o r t h e M O S T b a s e l i n e o r b i t i s s h o w n i n F i g u r e 5.3. A l s o s h o w n is the c a s e f o r a s t o r m y m a g n e t o s p h e r e d i s r u p t e d b y a l a r g e C M E . 5 10 15 Cutoff (GV) Figure 5.3 Geomagnetic transmission function for the MOST baseline orbit, for normal magnetospheric conditions (no storm). 6 3 5.3 Trapped Protons and Electrons A l o n g w i t h s o l a r e n e r g e t i c p a r t i c l e s , the t r a p p e d p r o t o n a n d e l e c t r o n p o p u l a t i o n s are the m o s t s i g n i f i c a n t i n the M O S T b a s e l i n e o r b i t . A P 8 a n d A E 8 m o d e l s ( S e c t i o n 3 .2) w e r e u s e d to e v a l u a t e p a r t i c l e f l u e n c e o v e r a s p e c i f i e d m i s s i o n l i f e t i m e . F o r t h e M O S T m i c r o s a t e l l i t e , it is p o s s i b l e to c o m p l e t e a l l p r i m a r y s c i e n c e o b j e c t i v e s w i t h i n m i n i m u m m i s s i o n l i f e t i m e ( o n e y e a r ) . T h u s , the f l u e n c e l e v e l s p r e s e n t e d h e r e are a n o r b i t - i n t e g r a t e d f l u x ( p a r t i c l e p e r u n i t a r e a p e r y e a r ) o v e r t h e b a s e l i n e y e a r l o n g m i s s i o n . F i g u r e 5.4 s h o w s t h e i n t e g r a l f l u e n c e o f t r a p p e d p r o t o n s a n d e l e c t r o n s f o r the M O S T b a s e l i n e o r b i t f o r b o t h s o l a r m a x i m u m a n d s o l a r m i n i m u m ( m i n i m u m m i s s i o n d u r a t i o n o f 1 y e a r ) . S i n c e t h e t r a p p e d m a g n e t o s p h e r i c p o p u l a t i o n i s i n s i d e t h e m a g n e t o s p h e r e , n o g e o m a g n e t i c s h i e l d i n g is a p p l i e d . T h e p r o t o n f l u x v a r i e s b y a b o u t a l.OE+15 7 — 1 10 100 1000 Energy (MeV) Figure 5.4 Proton and electron fluence over M O S T minimum mission lifetime. 6 4 f a c t o r o f 2 b e t w e e n s o l a r m a x i m u m a n d s o l a r m i n i m u m . H i g h e r f l u e n c e d u r i n g s o l a r m i n i m u m are e x p e c t e d d u e t o a t m o s p h e r i c e x p a n s i o n ( S e c t i o n 2.5) . S i n c e h i g h e r e n e r g y p a r t i c l e s are a l s o m o r e p e n e t r a t i n g t o t h e s h i e l d i n g o f s p a c e c r a f t , t h e h i g h - e n e r g y p r o t o n p o p u l a t i o n s are t h e m o s t i m p o r t a n t to c o n s i d e r . A p p e n d i x D c o n t a i n s m a p s s h o w i n g t h e p a r t i c l e e n v i r o n m e n t s f o r 0.1 M e V , 10 M e V , a n d 3 0 0 M e V p r o t o n s as w e l l as 1 M e V , a n d 5 M e V e l e c t r o n s r e s p e c t i v e l y . T h e m o s t d o m i n a n t f e a t u r e is the S A A , as e x p e c t e d . L o w e r e n e r g y p a r t i c l e s , e s p e c i a l l y t h e l o w e r e n e r g y e l e c t r o n s , are a l s o f o u n d to o c c u p y b a n d s i n h i g h l a t i t u d e s . A t h i g h o r l o w l a t i t u d e s , t r a p p e d m a g n e t o s p h e r i c p a r t i c l e s i n the o u t e r r a d i a t i o n b e l t s c a n r e a c h l o w a l t i t u d e s . T h e s e ' h o r n s ' are m u c h less s t a b l e t h a n t h e S A A as t h e y are a s s o c i a t e d w i t h t h e o u t e r m a g n e t o s p h e r e o f t h e E a r t h a n d d y n a m i c a l l y i n t e r a c t w i t h the s o l a r w i n d a n d a s s o c i a t e d m a g n e t i c f i e l d s . H e n c e u n c e r t a i n t i e s i n the f l u e n c e o f t h o s e p a r t i c l e s are h i g h e r t h a n e s t i m a t e d h e r e . S i n c e t h e y a r e l o w - e n e r g y p a r t i c l e s a n d w o n ' t b e a b l e to p e n e t r a t e s p a c e c r a f t s h i e l d i n g , a m o r e c o m p r e h e n s i v e t r e a t m e n t o f t h e u n c e r t a i n t y o f the f l u e n c e f o r t h i s p o p u l a t i o n w a s n o t u n d e r t a k e n . 5.4 Galactic Cosmic Radiation T h e G a l a c t i c C o s m i c R a d i a t i o n c o m p o n e n t w a s c a l c u l a t e d u s i n g C R E M E ( S e c t i o n 3.4) . I n t e g r a l a n d d i f f e r e n t i a l f l u x s p e c t r a f o r the M O S T m i c r o s a t e l l i t e d u e to G C R d u r i n g s o l a r m a x i m u m a n d m i n i m u m u n d e r n o r m a l g e o m a g n e t o s p h e r i c c o n d i t i o n s w i t h a 3 - D s h i e l d i n g r e p r e s e n t a t i o n o f t h e c a v i t y i n w h i c h the c h a r g e d c o u p l e d d e v i c e ( C C D ) r e s i d e s a p p l i e d ( S e c t i o n 1.3.1 & 5.7) are s h o w n i n F i g u r e s 5.5 a n d 5 .6 r e s p e c t i v e l y . 65 Figure 5.5 Integral flux energy spectrum of G C R expected to hit the C C D detector. 66 1 i 1 10 100 1000 10000 Energy (MeV/nuc.) Figure 5.6 Differential flux of GCR penetrating behind a 3-D shielding geometry. This is the GCR flux expected to hit the CCD detector. 67 T h e 1 M e V i n t e g r a l f l u x d u e to G C R i n s i d e t h e M O S T s p a c e c r a f t i s a b o u t 1 0 0 G 7 ( m 2 sr s) , y i e l d i n g a o n e y e a r f l u e n c e o f 2.14 x 1 0 1 0 / m 2 / s r . C o m p a r e d to t h e p r o t o n 10 f l u e n c e i n s i d e the s p a c e c r a f t (~2 x 10 f o r 1 M e V p r o t o n s ; S e c t i o n 5 .3) the G C R is a b o u t 2 o r d e r s o f m a g n i t u d e l o w e r t h a n the t r a p p e d p r o t o n f l u x . T h u s , the c u m u l a t i v e i o n i s i n g d o s e d u e to G C R w i l l b e n e g l i g i b l e c o m p a r e d t o the p o p u l a t i o n s t r a p p e d i n the V a n A l l e n R a d i a t i o n b e l t s . H o w e v e r , s i n c e t h e G C R i o n s a r e m u c h h e a v i e r , t h e y c r e a t e m o r e S i n g l e E v e n t U p s e t s ( S E U s , S e c t i o n 6.2) t h a n the p r o t o n p o p u l a t i o n . 5.5 Anomalous Cosmic Radiation T h e i n t e g r a l a n d d i f f e r e n t i a l flux d u e to A C R as p r e d i c t e d b y C R E M E , p r o p a g a t e d t h r o u g h t h e E a r t h ' s g e o m a g n e t o s p h e r e a n d 5 m m o f A l c y l i n d r i c a l s h i e l d i n g ( S e c t i o n 5.7), a re s h o w n i n F i g u r e 5.7. T h e s e s p e c t r a s c a l e to l a r g e r f l u x e s w i t h less s h i e l d i n g a n d v i c e v e r s a f o r a d d i t i o n a l s h i e l d i n g . T h e l a r g e r f i r s t i o n i s a t i o n p o t e n t i a l o f N r e l a t i v e t o O r e s u l t s i n t h e f l u x o f N i n the A C R b e i n g s l i g h t l y h i g h e r t h a n that o f O . 6 8 Figure 5.7 Integral and differential flux energy spectra of ACR. 5.6 Solar Energetic Particles T h e e n e r g y s p e c t r a a s s o c i a t e d w i t h the 5 d i f f e r e n t S E P e v e n t s d e s c r i b e d i n S e c t i o n 3 .5 are s h o w n i n F i g u r e 5 .8 , a g a i n w i t h g e o m a g n e t o s p h e r i c a n d 5 m m o f A l c y l i n d r i c a l s p a c e c r a f t s h i e l d i n g ( S e c t i o n 5.7) a p p l i e d . T h e J P L 1991 is t h e m o s t r e l i a b l e a n d s t a t i s t i c a l l y a c c u r a t e m o d e l . H o w e v e r , it r e p r e s e n t s d a t a a v e r a g e d o v e r a 5 - y e a r t i m e f r a m e . S i n c e M O S T is b e i n g l a u n c h e d d u r i n g the d e c l i n e o f s o l a r m a x i m u m , it is m o r e l i k e l y that a l a r g e S E P e v e n t w i l l o c c u r . 6 9 F i g u r e 5.8 Differential energy spectra of S E P events. 7 0 5.7 Satellite Shielding R e f e r r i n g b a c k to F i g u r e 3.1 a n d the a p p r o a c h to m o d e l i n g the r a d i a t i o n e n v i r o n m e n t , the n e x t s t e p i n the r a d i a t i o n a n a l y s i s f o r t h e M O S T m i c r o s a t e l l i t e i s a p p a r e n t . T h e c o n t r i b u t i o n s d u e to g a l a c t i c c o s m i c r a y s , s o l a r p r o t o n s a n d m a g n e t o s p h e r i c p a r t i c l e s a l l c o n t r i b u t e to the s p a c e c r a f t i n c i d e n t fluence. H o w e v e r , s h i e l d i n g s t o p s m a n y o f the i n c i d e n t p a r t i c l e s f r o m i n t e r a c t i n g w i t h s p a c e c r a f t s e n s i t i v e c o m p o n e n t s . T h u s , the s h i e l d i n g o f t h e M O S T d e s i g n m u s t n o w b e c o n s i d e r e d . S i m p l e S h i e l d i n g G e o m e t r y T h e f i rs t s tep i n t h e r a d i a t i o n a n a l y s i s i s a n a s s e s s m e n t o f t h e r a d i a t i o n e n v i r o n m e n t b e h i n d s t a n d a r d s i m p l e s h i e l d i n g m o d e l s . T h e t h r e e m o d e l s f o r s i m p l e s h i e l d i n g i n c l u d e d w i t h the S H L E L D O S E - 2 c o d e d e v e l o p e d b y A l V a m p o l a ( 1 9 9 6 ) are (1 ) a f i n i t e A l s l a b , (2) a s e m i - i n f i n i t e A l s l a b , a n d (3) a n A l s p h e r e . T h e r e s u l t s f o r t h e S H I E L D O S E - 2 c a l c u l a t i o n s f o r the M O S T b a s e l i n e o r b i t are s h o w n i n F i g u r e 5 .9 . I n c l u d e d i s t h e d o s e v s . d e p t h p r o f i l e s f o r t r a p p e d p r o t o n s a n d e l e c t r o n s f r o m A P 8 / A E 8 d u r i n g s o l a r m a x i m u m , as w e l l as s o l a r p r o t o n s f r o m the J P L 9 1 m o d e l c o n t r i b u t i n g to t h e t o t a l d o s e i n s i d e a n A l s p h e r e . I n c l u d e d i n t h e e l e c t r o n d o s e i s b r e h m s t r a h l u n g e m i s s i o n . S i n c e the d o s e v s . d e p t h c u r v e s o f t h e s i m p l e s h i e l d i n g g e o m e t r y a n a l y s i s l e v e l o f f , the a d v a n t a g e s o f t h i c k e r s h i e l d i n g start t o d e c l i n e , e s p e c i a l l y as t h i c k e r s h i e l d i n g q u i c k l y a d d s m a s s t o t h e sa te l l i te . T h u s , i n b a l a n c i n g s h i e l d i n g v s . less m a s s , t h e o p t i m a l s h i e l d i n g t h i c k n e s s a p p e a r s to b e a r o u n d 5 m m f r o m F i g u r e 5 .9 ( a d d i t i o n a l s h i e l d i n g d o s e n o t r e d u c e o v e r a l l d o s e s i g n i f i c a n t l y ) . A c r i t i c a l d o s e f o r M O S T i s o n t h e o r d e r o f 10 k r a d i n S i ( o n e r a d is e q u i v a l e n t to 1 0 0 e r g s o f e n e r g y a b s o r b e d b y 1 g r a m o f m a t e r i a l ) , s o t h e m i n i m u m a m o u n t o f s h i e l d i n g n e e d e d i s c o n s e r v a t i v e l y e s t i m a t e d as 3 m m . H o w e v e r , s i n c e p r e l i m i n a r y e s t i m a t e s o f m i n i m u m s h i e l d i n g t h i c k n e s s w e r e 10 m m ( M a t t h e w s , 1997 ) , t h e r e v i s e d m i n i m u m e s t i m a t e o f 5 m m o f A l s h i e l d i n g i s s u f f i c i e n t to e n s u r e t h e d u r a t i o n o f t h e m i s s i o n f o r j u s t l e s s t h a n 10 y e a r s , as w e l l as r e d u c e s o v e r a l l m a s s o f t h e i n s t r u m e n t . 10000000 71 10-1 ! i 1 — 1 1 0 5 10 15 20 Depth in Al(im) Figure 5.9 Dose vs. Depth curve for simple shielding geometry based on SHIELDOSE-2. The red line is for a 4 Pi Al Spherical shield, the pink for an infinite Al slab, and the blue for a finite Al slab. Also shown are contributions from trapped protons, JPL91 SEP, and trapped electrons for the Al spherical shielding case. 3-D Shielding Models O f c o u r s e , t h e M O S T sa te l l i te i s n e i t h e r a s p h e r e n o r a p l a n e s l a b . O n c e the d e s i g n w a s s i g n i f i c a n t l y m a t u r e ( i n c o r p o r a t i n g p r e l i m i n a r y s h i e l d i n g r e c o m m e n d a t i o n s ) , a m o r e d e t a i l e d s h i e l d i n g m o d e l w a s g e n e r a t e d u s i n g S P A C E R A D I A T I O N 4 . 0 . A n e n g i n e e r i n g s c h e m a t i c o f the M O S T sa te l l i te i s s h o w n i n F i g u r e 5 . 1 0 , a l o n g w i t h a s c h e m a t i c o f the 3 - D c y l i n d r i c a l m o d e l u s e d to g e n e r a t e t h e c u m u l a t i v e d o s e s o f the M O S T m i s s i o n . T h e t e l e s c o p e s t r u c t u r e i t s e l f , a p p r o x i m a t e l y a n 8 - m m t h i c k c y l i n d e r o f I N V A R ( a s teel a l l o y ) ac t s as s h i e l d i n g . T h e m o s t s e n s i t i v e c o m p o n e n t w i t h i n the s a t e l l i t e s t r u c t u r e i s the C h a r g e d C o u p l e d D e v i c e ( C C D ) w h i c h sits a b o u t 3/4 o f t h e w a y t o w a r d s t h e b a c k o f t h e t e l e s c o p e . I m m e d i a t e l y s u r r o u n d i n g the C C D is the c a m e r a h o u s i n g , a n o t h e r c y l i n d e r a b o u t 2 m m t h i c k a n d m a d e o f T i . 7 2 449 mm Figure 5.10 Engineering schematic of the preliminary MOST satellite design (top) and schematic of 3-D shielding geometry used to represent satellite shielding. The outer casing is representative of the telescope tube, and the inner casing is representative of the camera housing. 73 A l u m i n u m ( o r A l e q u i v a l e n t ) s h i e l d i n g r e m o v e s l o w - e n e r g y p a r t i c l e s m o r e e f f e c t i v e l y t h a n h i g h - e n e r g y p a r t i c l e s . F i g u r e 5 .11 i l l u s t r a t e s t h i s b y c o m p a r i n g t h e t r a p p e d p r o t o n i n t e g r a l f l u e n c e s p e c t r a f o r a n o n - s h i e l d e d , a n d a s h i e l d e d c a s e ( i n s i d e t u b e 5 - m m t h i c k w i t h the M O S T t e l e s c o p e d i m e n s i o n s ) . R e c a l l that i n t e g r a l f l u e n c e is t h e f l u x i n t e g r a t e d o v e r a b a s e l i n e m i s s i o n l i f e t i m e o f o n e y e a r . 1.00E+15 -j 1.00E+09 H 1 1 1 1 1 0.1 1 10 100 1000 Energy (MeV) Figure 5.11 Comparison of the integral trapped proton fluence outside the spacecraft, and behind 5 mm of Al cylindrical shielding with the MOST satellite dimensions as shown in T h e c h a r g e d p a r t i c l e m u s t p e n e t r a t e t h e s h i e l d i n g w i t h s u f f i c i e n t e n e r g y to f u r t h e r p e n e t r a t e i n t o the s e n s i t i v e v o l u m e o f the s p a c e c r a f t c o m p o n e n t to d o a n y d a m a g e . T h u s , the i n c i d e n t s p e c t r a are d e s c r i b e d i n t e r m s o f the l i n e a r e n e r g y t r a n s f e r o r L E T s p e c t r u m ( F i g u r e 5 .12) . L E T i s a m e a s u r e o f the rate o f e n e r g y d e p o s i t i o n i n a s e n s i t i v e v o l u m e o f t h e d e v i c e p e r u n i t p a t h l e n g t h . It i s e s s e n t i a l l y a d e s c r i p t i o n o f t h e a b i l i t y o f t h e p a r t i c l e 7 4 t o t r a n s f e r its e n e r g y i n t o c r y s t a l l a t t i c e o f the d e v i c e , o r i n t o i o n i s i n g o n e o f t h e a t o m s . O f c o u r s e , t h e L E T is d e p e n d e n t o n the d e v i c e s t ruc ture i t s e l f , w h a t it i s m a d e o f a n d h o w e a s i l y the b o n d s b e t w e e n m o l e c u l e s are b r o k e n . S i n c e the m a j o r i t y o f e l e c t r o n i c s are b a s e d o n a S i l i c o n c r y s t a l l a t t i c e , the L E T p r e s e n t e d h e r e are f o r S i d e t e c t o r s . K n o w i n g t h e L E T t h r e s h o l d s o f t h e d e v i c e s o n b o a r d the s p a c e c r a f t a l l o w s a d i r e c t c o m p a r i s o n b e t w e e n the r a d i a t i o n e n v i r o n m e n t a n d the s e n s i t i v e c o m p o n e n t s . F i g u r e s 5 .12 a n d 5 .13 s h o w t h e L E T s p e c t r a f o r t r a p p e d p r o t o n s a n d S E P ( J P L 9 1 ) r e s p e c t i v e l y d u r i n g s o l a r m a x i m u m f o r 3 d i f f e r e n t s h i e l d i n g m o d e l s . F i g u r e 5 . 1 4 s h o w s the L E T s p e c t r a f o r G C R . S i n c e the m a j o r i t y o f t h e i o n s i n G C R are h e a v y i o n s , t h e L E T is n o t s e n s i t i v e to the s h i e l d i n g m o d e l . 1.00E+13T I.OOETOS-1 j . , I ; 1 10 100 1000 LCT(IVfev/(g'cm2)) Figure 5.12 LET Spectra of trapped Protons for (a) 2 mm Ti shielding with MOST camera housing dimensions, (b) 5 mm Al shielding with MOST telescope tube dimensions, and (c) 8 mm Al shielding with MOST telescope tube dimensions. 75 l.OOE+06 -I 1 1 « 1 1 10 100 1000 L E T (MeV/Cgfan2) Figure 5.13 LET spectra of solar energetic protons as modeled by JPL91. 1.00E+11 T 1.00E-05 -1 1 1 1 1 1 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 LET (MeV/(g/cm2)) Figure 5.14 LET spectra due to GCR. 7 6 5.8 Cumulative doses C h a r g e d p a r t i c l e s i n t e r a c t w i t h S i l i c o n b a s e d e l e c t r o n i c s o n b o a r d i n t h e sa te l l i te i n t h r e e w a y s : (a) i o n i s a t i o n , (b) d i s p l a c e m e n t , o r (c ) S E U ( S e c t i o n 6.2) . W h e t h e r a p r o t o n w i l l c a u s e i o n i s a t i o n d a m a g e o r d i s p l a c e m e n t d a m a g e d e p e n d s o n t h e i n c i d e n t p a r t i c l e ' s e n e r g y . T h e L E T s p e c t r a c o n t a i n i n f o r m a t i o n o n w h e t h e r t h e p a r t i c l e w i l l d a m a g e t h e e l e c t r o n i c d e v i c e t h r o u g h i o n i s a t i o n o r d i s p l a c e m e n t . H e n c e , t h e r e are t w o c u m u l a t i v e d o s e s to b e c a l c u l a t e d : i o n i s a t i o n d o s e a n d d i s p l a c e m e n t d o s e . C u m u l a t i v e a n d d i s p l a c e m e n t d o s e s are t a b u l a t e d i n A p p e n d i x E . M O S T w i l l e x p e r i e n c e a b o u t 1 k r a d o f i o n i s i n g d o s e p e r y e a r . S i n c e o n l y the t e l e s c o p e i t s e l f h a s b e e n c o n s i d e r e d as s h i e l d i n g , t h i s i s a v e r y c o n s e r v a t i v e e s t i m a t e . T h e sa te l l i te s t r u c t u r e i t s e l f w i l l c o n t r i b u t e a d d i t i o n a l s h i e l d i n g . I f t h e r e i s a l a r g e f l a r e a n d a l a r g e g e o m a g n e t i c d i s t u r b a n c e , t h e n M O S T c o u l d e x p e r i e n c e a n a d d i t i o n a l k r a d i o n i s i n g d o s e . A g a i n , a c c o r d i n g to r e c e n t e x p e r i e n c e , t h i s i s a g r o s s l y c o n s e r v a t i v e n u m b e r . T h e g o o d n e w s is that M O S T s h o u l d b e a b l e to w i t h s t a n d e v e n the h a r s h e s t r a d i a t i o n e n v i r o n m e n t i t i s l i k e l y to e n c o u n t e r i n the r a n g e o f o r b i t s c o n s i d e r e d f o r it. T o t a l d i s p l a c e m e n t d a m a g e w i l l b e o n t h e o r d e r o f 0 .7 r a d s i n S i , o r 7 x 1 0 8 1 M e V p r o t o n e q u i v a l e n t s / c m 2 ) . O n e r a d ( S i ) i s a p p r o x i m a t e l y e q u i v a l e n t to a f l u x o f 4 x 1 0 7 ( e n e r g y - l M e V ) i o n i s i n g p a r t i c l e s / c m 2 ( B a i l e y 1996) . T h e e f f e c t s o f the d i s p l a c e m e n t d a m a g e as w e l l as the i o n i s i n g d o s e a r e f u r t h e r i n v e s t i g a t e d i n C h a p t e r 6. T h e u n c e r t a i n t i e s i n t h e r a d i a t i o n e n v i r o n m e n t m o d e l s are d i s c u s s e d i n S e c t i o n 3 .6 . T a b l e 5.1 s u m m a r i z e s the e s t i m a t e d u n c e r t a i n t i e s i n the m o d e l s . D o s e s c a l c u l a t e d u s i n g t h e s e m o d e l s are o n l y as g o o d as t h e m o d e l s t h e m s e l v e s . Particle Population Model Uncertainty Under/Over-prediction T r a p p e d P r o t o n s A P 8 1 .7-2.0 U n d e r - p r e d i c t i o n T r a p p e d E l e c t r o n s A E 8 2 O v e r - p r e d i c t i o n S o l a r P r o t o n s J P L 1 9 9 1 9 7 % a c c u r a c y D e p e n d s o n F l a r e N u m b e r G C R C R E M E 2-5 D e p e n d s o n S o l a r M a x / M i n A C R C R E M E G r o s s O v e r - p r e d i c t i o n Table 5.1 Uncertainty in radiation environment models. 7 7 5.9 Dose versus Altitude A l t h o u g h t h e r e a r e m a n y a r g u m e n t s f a v o r i n g t h e b a s e l i n e o r b i t , t h e r e i s n o g u a r a n t e e that the M O S T m i c r o s a t e l l i t e w i l l e n d u p i n i ts i d e a l o r b i t . T h u s , the d o s e as i t v a r i e s w i t h o r b i t a l a l t i t u d e o v e r a set o f s u n - s y n c h r o n o u s o r b i t s h a s b e e n e v a l u a t e d f o r q u i e t m a g n e t o s p h e r i c c o n d i t i o n s at s o l a r m a x i m u m i n t h e c e n t e r o f a n a l u m i n u m s p h e r e (as p e r s i m p l e s h i e l d i n g g e o m e t r y d e s c r i b e d i n S e c t i o n 5.7) . A s e x p e c t e d , t h e d o s e i n c r e a s e s v e r y s l i g h t l y at h i g h e r a l t i t u d e s as t h e o r b i t c r e e p s u p w a r d i n t o t h e h e a r t o f the V a n A l l e n R a d i a t i o n b e l t s . A s s h o w n i n F i g u r e 5 .15 the d o s e i n c r e a s e s b y a b o u t 5 0 k r a d p e r y e a r p e r 100 k m i n c r e a s e i n o r b i t a l a l t i t u d e ( w i t h 5 m m o f A l s h i e l d i n g ) . 0 2 4 6 8 10 12 14 16 18 20 Alumiiumum Shielding Thickness (mm) Figure 5.15 Dose at the center of an Aluminum Sphere for heliosynchronous orbits with different altitudes ranging from 600 to 1000 km. T h e S A A c o v e r s a m u c h l a r g e r a r e a at h i g h e r a l t i t u d e , as the o r b i t a l p l a n e c r e e p s u p w a r d i n t o t h e hear t o f t h e V a n A l l e n R a d i a t i o n B e l t s . A t 1 0 0 0 k m , e n e r g e t i c p a r t i c l e s f r o m b o t h h o r n s w i l l b o m b a r d t h e sate l l i te . F i g u r e 5 .16 s h o w s t h e o u t l i n e o f t h e S A A at 7 8 6 0 0 k m , 8 0 0 k m , a n d 1 0 0 0 k m . S i n c e d a t a c o l l e c t i o n m a y b e r e d u c e d f o r m u c h o f t h e h i g h e n e r g y r e g i o n s o f t h e S A A , M O S T s h o u l d n o t c o n s i d e r i n c r e a s i n g o r b i t a l a l t i t u d e s i g n i f i c a n t l y . Figure 5.16 Approximate boundary of the SAA at 600, 800, and 1000 km altitude. 7 9 Chapter 6: Rain or Shine? Implications of Space Weather on MOST T h e p r i m a r y e f f e c t s o f t h e r a d i a t i o n e n v i r o n m e n t o n the M O S T m i c r o s a t e l l i t e are t h e f o l l o w i n g : (a) i o n i s i n g p a r t i c l e s w i l l d a m a g e t h e C C D a n d e l e c t r o n i c s ( i n c l u d i n g d e g r a d a t i o n o f c h a r g e t r a n s f e r e f f i c i e n c y ( C T E ) a n d l o c a l i s e d 'hot ' r e g i o n s o f p e r m a n e n t l y d a m a g e d p i x e l s ) ; ( b ) h i g h e n e r g y p a r t i c l e s w i l l a l te r s t r u c t u r e o f s i l i c a la t t i ce i n e l e c t r o n i c s c a u s i n g d i s p l a c e m e n t d a m a g e ; ( c ) s i n g l e e v e n t e f f e c t s ( S E E s ) ; (d ) a n d a r e d u c e d d u t y c y c l e f r o m a p o s s i b l e l o s s o f o b s e r v a t i o n s t h r o u g h t h e S A A ( S e c t i o n 4 .4) . T o u n d e r s t a n d h o w s e r i o u s e f f e c t s (a) - ( c ) a r e , i t is n e c e s s a r y t o e x a m i n e the C C D d e t e c t o r s to b e u s e d o n M O S T . A p p e n d i x F c o n t a i n s t h e S p e c i f i c a t i o n S h e e t f o r the o f f -t h e - s h e l f v e r s i o n o f the M O S T C C D . T h e r a d i a t i o n s p e c i f i c a t i o n o f the C C D ( S e c t i o n 1.4) i s s u e d b y M a r c o n i i s t h e f o l l o w i n g : " D e v i c e p a r a m e t e r s m a y b e g i n to c h a n g e i f s u b j e c t to g r e a t e r t h a n 1 0 4 rads . T h i s c o r r e s p o n d s to 1 0 1 3 o f 15 M e V n e u t r o n s / c m 2 , 2 x 1 0 1 3 o f 1 M e V g a m m a / c m 2 , o r 4 x 1 0 1 1 o f i o n i s i n g p a r t i c l e s / c m . " ( M a r c o n i 2 0 0 0 ) M a r c o n i c o n d u c t s m a n y r a d i a t i o n tests o f t h e i r o w n C C D s i n o r d e r to p r o v i d e t h e i r c u s t o m e r s w i t h e s t i m a t e s o f the c h a n g e i n s p e c i f i c a t i o n w i t h r a d i a t i o n d e g r a d a t i o n . T h u s , t h e d o c u m e n t p r e p a r e d b y R o b b i n s ( 2 0 0 0 ) o n t h e p e r f o r m a n c e o f M a r c o n i C C D s u n d e r r a d i a t i o n d a m a g e i s u t i l i s e d to e v a l u a t e t h e p e r f o r m a n c e o f the M O S T C C D i n t h e e n v i r o n m e n t d e s c r i b e d i n C h a p t e r 5. 80 6.1 CCD Damage C C D t e c h n o l o g y h a s a d v a n c e d g r e a t l y i n the p a s t d e c a d e i n r e s p o n s e to d e m a n d s f o r b e t t e r s c i e n t i f i c i m a g i n g . H o w e v e r , the i n c r e a s e i n s e n s i t i v i t y o f C C D s h a s b e e n at the p r i c e o f a n i n c r e a s e d s e n s i t i v i t y to r a d i a t i o n d a m a g e i n s p a c e t h r o u g h (1) i o n i s a t i o n d a m a g e , a n d (2) d i s p l a c e m e n t d a m a g e . I o n i s a t i o n d a m a g e , as s h o w n i n F i g u r e 6 .1, c a n h a v e t w o e f f e c t s o n C C D s . I f a n i n c o m i n g e n e r g e t i c p a r t i c l e h i t s the s e m i c o n d u c t o r la t t i ce , it acts m u c h l i k e a n i n c o m i n g s i g n a l p h o t o n w o u l d , f r e e i n g a n e l e c t r o n a n d l e a v i n g a n d e l e c t r o n - h o l e p a i r . T h e e l e c t r o n is f r e e d a n d a n e l e c t r o n - h o l e p a i r r e m a i n s . H o w e v e r , the e l e c t r o n - h o l e p a i r s t e n d to c o n g r e g a t e at the o x i d e - c o n d u c t o r i n t e r f a c e , c r e a t i n g a p o s i t i v e c h a r g e b u i l d u p at the i n t e r f a c e . T h i s d i r e c t l y s h i f t s the f l a t - b a n d p o t e n t i a l o f the C C D . M i d - g a p t r a p p i n g states are a l s o g e n e r a t e d , c r e a t i n g a n i n c r e a s e i n d a r k c u r r e n t t h r o u g h t h e r m a l ' h o p p i n g ' o f e l e c t r o n s . D e e p t r a p p i n g states a l s o are c r e a t e d , r e d u c i n g C T E ( c h a r g e t r a n s f e r e f f i c i e n c y , S e c t i o n 6 .1 .5) . Photon or charged particle Electron is collected as signal Figure 6.1 Charge generation or ionisation damage occur in the same manner in CCDs 81 2 I o n i s a t i o n i s s t r o n g l y d e p e n d e n t o n t h e c h a r g e o f the i n c o m i n g i o n s q u a r e d , Z . T h u s , t h e m o r e a b u n d a n t , l o w e r Z i o n s c a n d o as m u c h d a m a g e as the less a b u n d a n t , h i g h e r Z p a r t i c l e s ( T r i b b l e et a l . 1999) . D i s p l a c e m e n t d a m a g e ( o r b u l k d a m a g e ) h a s m o r e l a s t i n g e f f e c t s o n C C D s . A n i n c o m i n g p a r t i c l e ( p r o t o n o r h i g h - e n e r g y n e u t r o n ) s t r i k e s the la t t ice o f the s e m i -c o n d u c t o r a n d d i s p l a c e s o n e o f the ( S i ) a t o m s i n the la t t i ce , l e a v i n g a v a c a n c y as s h o w n i n F i g u r e 6.2. T h e v a c a n c i e s t e n d to c o n g r e g a t e t o g e t h e r a n d a r o u n d i m p u r i t i e s i n the l a t t i c e , c r e a t i n g p e r m a n e n t t r a p p i n g states w i t h i n t h e s e m i - c o n d u c t o r i tself . S h a l l o w t r a p p i n g states i n c r e a s e d a r k c u r r e n t a n d d e e p t r a p p i n g states b o t h d e c r e a s e C T E a n d i n c r e a s e r e a d n o i s e s i m i l a r l y to i o n i s a t i o n d a m a g e . " H o t " p i x e l s , o r r e g i o n s w i t h e x t r e m e i n t e n s i t i e s u n r e l a t e d to the s i g n a l , d e v e l o p w h e r e the v a c a n c i e s c o n g r e g a t e , d u e to the e x t r e m e d a r k c u r r e n t a s s o c i a t e d w i t h the m i d - g a p t r a p p i n g states. Figure 6.2 An energetic particle strikes a Si atom of the semiconductor lattice and kinks the structure, leaving a vacancy. Vacancies congregate together and about impurities in the crystal lattice. (After Hardy 1997) 82 E i t h e r i o n i s a t i o n d a m a g e o r b u l k d a m a g e w i l l i n d u c e t h e f o l l o w i n g : (a) D a r k c u r r e n t i n c r e a s e d u e to i o n i s i n g r a d i a t i o n ; (b) D a r k c u r r e n t i n c r e a s e d u e to b u l k d a m a g e ; ( c ) D a m a g e d p i x e l s ; (d ) R a n d o m t e l e g r a p h s i g n a l s ; (e) F l a t b a n d v o l t a g e s h i f t s ; ( f ) C T E d e g r a d a t i o n . 6.1.1 Dark Current I n e v e r y C C D , s o m e c u r r e n t i s g e n e r a t e d e v e n w h e n p h o t o n s are n o t i n c i d e n t o n t h e d e t e c t o r . T h i s b a c k g r o u n d s i g n a l i s c a l l e d the dark current. S i n c e d a r k c u r r e n t g e n e r a t i o n c rea tes a r a n d o m n u m b e r o f e l e c t r o n s p e r p i x e l , it i s a n o i s e s o u r c e . D a r k c u r r e n t i s p r i m a r i l y a t h e r m a l e f f e c t . I f e l e c t r o n s i n t h e v a l e n c e b a n d ( o r i n t h e v a l e n c e s h e l l s o f s i l i c o n i n t h e c r y s t a l la t t i ce ) p o s s e s s e n o u g h e n e r g y , t h e n t h e y m o v e to t h e c o n d u c t i o n b a n d , i . e . , t o the i n v e r s i o n l a y e r w h e r e t h e y are t r a p p e d a n d t h e n c o l l e c t e d as s i g n a l . T h u s , i f a n e l e c t r o n i n the v a l e n c e b a n d p o s s e s s e s s u f f i c i e n t t h e r m a l e n e r g y , i t c a n b e a t t r a c t e d t o t h e c o n d u c t i o n b a n d w i t h o u t a d d e d e n e r g y g e n e r a t e d b y t h e p h o t o e l e c t r i c e f f e c t o r b y i n t e r a c t i o n s w i t h a c h a r g e d p a r t i c l e . T h e p r o b a b i l i t y o f a n e l e c t r o n p o s s e s s i n g s u f f i c i e n t t h e r m a l e n e r g y to d o t h i s i s g i v e n b y the f o l l o w i n g f o r m u l a : p = I (6 .1) l + e^Ec-EfVkT w h e r e E c i s the e n e r g y o f e l e c t r o n s i n the c o n d u c t i o n b a n d , a n d E f i s the F e r m i e n e r g y o f t h e e l e c t r o n , k is the B o l t z m a n c o n s t a n t a n d T i s the o p e r a t i n g t e m p e r a t u r e o f the C C D ( H a r d y 1997) . T h u s , at l o w e r o p e r a t i n g t e m p e r a t u r e s , d a r k c u r r e n t i s s u p p r e s s e d . T h i s i s o n e o f t h e m a i n r e a s o n s to o p e r a t e the M O S T C C D at - 4 0 ° C . C o o l e r t e m p e r a t u r e s w o u l d r e d u c e d a r k c u r r e n t e v e n f u r t h e r , b u t r e q u i r e a m o r e e x p e n s i v e c r y o g e n i c c o o l i n g s y s t e m as o p p o s e d to a p a s s i v e c o o l i n g m e c h a n i s m . D a r k c u r r e n t d u e to r a d i a t i o n d a m a g e c a n b e c r e a t e d b y e i t h e r i o n i s i n g o r b u l k d a m a g e . I o n i s i n g r a d i a t i o n i n d u c e s e n h a n c e d d a r k c u r r e n t b y i n c r e a s i n g t h e i n t e r f a c e state d e n s i t y o f the d e p l e t e d s u r f a c e areas o f t h e d e v i c e ( R o b b i n s 2 0 0 0 ) . I f a n i n c o m i n g 83 c h a r g e d p a r t i c l e i n t e r a c t s w i t h a s i l i c o n a t o m at t h e s i l i c o n - s i l i c o n d i o x i d e i n t e r f a c e ( i n a n o n - b u r i e d c h a n n e l d e v i c e ) , i t c a n c r e a t e a m i d - g a p t r a p p i n g state, e s s e n t i a l l y a l o w e r e n e r g y p a t h w a y f o r e l e c t r o n s to m o v e a b o u t i n the s i l i c o n la t t ice . T h i s e f f e c t i v e l y i n c r e a s e s the e n e r g y o f t h e v a l e n c e b a n d e l e c t r o n s , o r d e c r e a s e s the e f f e c t i v e e n e r g y o f t h e c o n d u c t i o n b a n d e l e c t r o n s as s e e n b y the v a l e n c e b a n d e l e c t r o n s . T h e r m a l h o p p i n g o f e l e c t r o n s i n c r e a s e s a n d the d a r k c u r r e n t o f the d e t e c t o r i n c r e a s e s . S i n c e t h e M O S T d e v i c e i s o p e r a t e d u n d e r i n v e r s i o n , the m a j o r i t y o f t h i s s u r f a c e g e n e r a t e d s i g n a l i s s u p p r e s s e d . H e n c e , t h e r e are n o t m a n y r a d i a t i o n tests to c o m p a r e to . T h e o n l y a b s o l u t e m e a s u r e m e n t h a s b e e n m a d e b y B r u n e i U n i v e r s i t y , b u t n o t o n a M a r c o n i d e v i c e . T h e y f o u n d a n i n c r e a s e o f 1.5 p A / c m 2 / k r a d ( S i ) , o r 15 e 7 p i x / s / k r a d ( S i ) at 3 0 ° C . T h e e f f e c t o f i o n i s i n g r a d i a t i o n d a m a g e o n d a r k c u r r e n t at - 4 0 ° C s h o u l d b e n e g l i g i b l e ( - 0 . 0 3 e 7 p i x / m i n / k r a d ) . D a r k s i g n a l i n c r e a s e s c a n a l s o b e c a u s e d b y d i s p l a c e m e n t d a m a g e . I n a s i m i l a r f a s h i o n to t h e c r e a t i o n o f m i d - g a p t r a p p i n g states i n t h e c a s e o f i o n i s a t i o n d a m a g e , b u l k d a m a g e a l s o r e s u l t s i n t h e f o r m a t i o n o f a l o w e r e n e r g y p a t h w a y f o r e l e c t r o n s . T h e b i g g e s t d i f f e r e n c e i s that t h e l o w e r e n e r g y p a t h w a y is n o w i n t h e b u l k s t r u c t u r e o f t h e p - t y p e s i l i c o n , as o p p o s e d to b e i n g c o n f i n e d t o t h e i n t e r f a c e r e g i o n . S i n c e t h e t r a p p i n g states c r e a t e d b y d i s p l a c e m e n t d a m a g e a r e v e r y g o o d at t r a n s f e r r i n g e l e c t r o n s t h r o u g h t h e r m a l h o p p i n g , t h e d i s r u p t e d la t t i ce c a n e s s e n t i a l l y b e c o n s i d e r e d a d a r k c u r r e n t g e n e r a t i o n c e n t e r . B u l k d a m a g e i s i n d e p e n d e n t o f b i a s state. S i n c e the s i g n a l g e n e r a t i o n c e n t e r s a r e i n t h e d e p l e t i o n r e g i o n a n d n o t i n t h e s u r f a c e r e g i o n , i n v e r s i o n w i l l n o t s u p p r e s s t h i s s i g n a l . T e s t s o f a T e k t r o n i k s b a c k s i d e i l l u m i n a t e d , b u r i e d c h a n n e l d e v i c e s i m i l a r to the M O S T C C D w e r e m a d e b y H a r d y ( 1 9 9 7 ) . F o r the d e v i c e r u n n i n g i n M P P m o d e , the b a s e l i n e d a r k c u r r e n t w a s less t h a n 1 e 7 p i x e l / s (at - 4 0 ° C ) . A f t e r i r r a d i a t i o n w i t h 6.0 x 1 0 9 3 M e V p r o t o n s / c m , the d a r k c u r r e n t i n c r e a s e d to 2 e 7 p i x e l / s , a n d af ter 1.5 x 10 3 M e V p r o t o n s / c m 2 , t h e s i g n a l w a s u p to 9 e 7 p i x e l / s , a g a i n at - 4 0 ° C . I n a w o r s t c a s e s c e n a r i o w i t h a n e x t r e m e l y l a r g e f l a r e e v e n t , M O S T w i l l see 1.93 x 10 1 M e V p r o t o n s / c m . T h u s , w e c a n e x p e c t a s m a l l i n c r e a s e i n d a r k c u r r e n t d u e t o b u l k r a d i a t i o n , o n t h e o r d e r o f 1 e" / p i x e l / s . B o t h e f f e c t s are t e m p e r a t u r e d e p e n d e n t . T h e i o n i s a t i o n d a m a g e i n c r e a s e i n d a r k c u r r e n t v a r i e s as j3^'7000^, w h e r e a s t h e d a r k c u r r e n t i n c r e a s e d u e t o b u l k d a m a g e i s 84 j2e(-7ooon) j j e n c e ; o p e r a t i n g at T ~ - 4 0 ° C i s v e r y i m p o r t a n t . T e m p e r a t u r e s t a b i l i t y i s a l s o v e r y i m p o r t a n t to s u p p r e s s d r i f t s i n t h e d a r k c u r r e n t . I n s u m m a r y , s i n c e M O S T is u s i n g a d e v i c e o p e r a t i n g i n i n v e r s i o n , m o s t o f t h e d a r k c u r r e n t i s s u p p r e s s e d . T h e t o t a l i n c r e a s e i n d a r k c u r r e n t d u e t o i o n i s a t i o n a n d b u l k d a m a g e i s o n the o r d e r o f 1 e " / p i x e l / s . 6.1.2 Damaged Pixels F r e q u e n t l y , d i s p l a c e m e n t d a m a g e o c c u r s i n m o r e t h a n o n e p l a c e i n t h e S i l a t t i c e i n t h e s a m e p i x e l . A h i g h e n e r g y p a r t i c l e c a n b o m b a r d the f i rs t S i a t o m i n the l a t t i c e , b e d e f l e c t e d , b u t c o n t i n u e o n its d e s t r u c t i v e p a t h t h r o u g h t h e d e v i c e . A l s o , i f d i s p l a c e m e n t d a m a g e o c c u r s i n t h e la t t i ce i n a r e g i o n w h e r e t h e r e i s a v e r y s t r o n g e l e c t r i c f i e l d a p p l i e d , t h e n t h e p i x e l w i l l s h o w a v e r y h i g h g e n e r a t i o n rate d u e to a s i g n i f i c a n t l o w e r i n g o f t h e p o t e n t i a l b a r r i e r . E l e c t r o n s w i l l f l o o d t h e p i x e l , m a k i n g it a p p e a r l i t . T h e v o l u m e o f a n y p i x e l i n a h i g h f i e l d r e g i o n is e x t r e m e l y s m a l l , s o t h i s i s a n u n l i k e l y e f f e c t ( R o b b i n s , p r i v a t e c o m m u n i c a t i o n ) . M a r c o n i e s t i m a t e s that ~ 0 . 1 % o f p i x e l s w i l l d i s p l a y a b o u t 3 1 , 5 0 0 e 7 p i x e l / s d u e to d a m a g e d p i x e l s a f t e r i r r a d i a t i o n w i t h 2 k r a d o f 10 M e V e q u i v a l e n t p r o t o n s . A l t h o u g h t h i s i s a v e r y s m a l l n u m b e r o f p i x e l s , t h e M O S T d a t a r e d u c t i o n a l g o r i t h m n e e d s to i n c l u d e a p r o c e s s f o r i d e n t i f y i n g p i x e l s w h i c h c o n s i s t e n t l y g i v e a s i g n a l a b o v e a c e r t a i n t h r e s h o l d , e v e n w h e n t h e r e i s n o l i g h t f a l l i n g o n that p i x e l . T h e l i t p i x e l s c a n e f f e c t i v e l y b e r e m o v e d f r o m t h e d a t a set, t h u s r e m o v i n g a n y n o i s e d u e t o t h e l i t p i x e l s . 85 6.1.3 R T S R a n d o m T e l e g r a p h S i g n a l i n g ( R T S ) i s a m o r e s i g n i f i c a n t t y p e o f p i x e l d a m a g e that the M O S T d a t a r e d u c t i o n a l g o r i t h m s h o u l d b e set to m o n i t o r . A l t h o u g h it i s u n c l e a r w h a t c a u s e s R T S ( i t d o e s n o t a p p e a r to b e c r e a t e d b y n u c l e a r i n t e r a c t i o n s ) , it i s d e f i n i t e l y a n e f f e c t s e e n i n e x p e r i m e n t s p e r f o r m e d o n M a r c o n i C C D s a n d e v a l u a t e d b y R o b b i n s ( 2 0 0 0 ) . A f t e r s i g n i f i c a n t p r o t o n i r r a d i a t i o n , s i n g l e p i x e l s b e g i n to s h o w f l u c t u a t i o n s i n t h e i r s i g n a l s , s h i f t i n g f r o m a l o w s i g n a l r e g i m e to a h i g h s i g n a l r e g i m e . T h e a m o u n t o f t i m e s p e n t i n o n e r e g i m e is n o t we}l c h a r a c t e r i z e d . H o w e v e r , t h e a v e r a g e t i m e s b e t w e e n t h e d i s c r e t e g e n e r a t i o n states i s w e l l d e f i n e d b y t h e f o l l o w i n g e q u a t i o n : c o n s t a n t (0 .9 ± 0.1 e V ) . T h e a v e r a g e t i m e p e r state is s t r o n g l y t e m p e r a t u r e d e p e n d e n t . A t t h e M O S T o p e r a t i n g t e m p e r a t u r e ( - 4 0 ° C ) , t h e t i m e c o n s t a n t is o n the o r d e r o f 6 d a y s . A b o u t 6 % o f the p i x e l s w i l l d i s p l a y R T S a f t e r o n e y e a r ( i .e . 6 0 , 0 0 0 p i x e l s w i l l b e d a m a g e d p e r 1 k r a d ) a n d the e f f e c t w i l l b e e n h a n c e d i n l i t p i x e l s . S i n c e t h e t i m e c o n s t a n t f o r R T S i s m u c h l o n g e r t h a n the o s c i l l a t i o n p e r i o d s that M O S T i s s e a r c h i n g f o r i n t h e s t e l l a r s i g n a l , t h i s e f f e c t w i l l n o t c r e a t e a l i a s e s i n the F o u r i e r f r e q u e n c y r e g i o n s o f interest . H o w e v e r , s i n c e t h e a c t u a l t i m e d u r a t i o n i n e a c h g e n e r a t i o n state i s n o t w e l l k n o w n , t h e r e c o u l d b e p h o t o m e t r i c n o i s e i n t r o d u c e d i n t h e r e g i o n o f in teres t w h e n a p i x e l d i s p l a y i n g R T S s tays i n o n e d i s c r e t e state f o r a p e r i o d o f t i m e s i g n i f i c a n t l y s h o r t e r t h a n i ts t i m e c o n s t a n t . T h u s , t h e M O S T d a t a r e d u c t i o n a l g o r i t h m n e e d s to i n c l u d e a m o n i t o r f o r t h i s e f f e c t , u t i l i s i n g o n b o a r d t e m p e r a t u r e s e n s o r d a t a to k e e p a n a c c u r a t e v a l u e f o r x. P i x e l s d i s p l a y i n g a n R T S e f f e c t s h o u l d b e d i s c a r d e d c o m p l e t e l y o r g i v e n v a l u e s t a k e n f r o m a n a v e r a g e o f t h e s u r r o u n d i n g p i x e l s . A l t h o u g h 6 % is a l a r g e n u m b e r o f to ta l p i x e l s , t h e d a t a that M O S T u s e s o n l y s p a n s 6 4 0 0 p i x e l s ( 0 . 6 % o f t h e t o t a l c h i p ) . T h u s , i t i s n o t l i k e l y that R T S w i l l r e s u l t i n a m a j o r l o s s o f d a t a f o r M O S T . (6 .2 ) T w h e r e t is t h e a v e r a g e t i m e i n e a c h state, R is a c o n s t a n t ( ~ 1 0 1 3 - 1 0 1 4 / s ) , a n d E i s a 86 6.1.4 Flat Band Voltage Shifts F l a t b a n d v o l t a g e s h i f t s o c c u r u n d e r i o n i s i n g r a d i a t i o n d a m a g e . T h e la t t ice o f the s i l i c o n d i o x i d e i n s u l a t i n g l a y e r i s n o t i m m u n e to i n t e r a c t i o n s w i t h c h a r g e d p a r t i c l e s . W h e n a n i o n i s i n g p a r t i c l e h i t s the la t t i ce i n t h e i n s u l t i n g r e g i o n , the h i g h e l e c t r i c f i e l d t e n d s to i m m e d i a t e l y s w e e p a w a y a n y e l e c t r o n s , l e a v i n g e l e c t r o n - h o l e p a i r s ( p o s i t i v e c h a r g e ) . A f t e r t i m e , the e l e c t r o n h o l e p a i r s a c c u m u l a t e a n d c o n g r e g a t e t o g e t h e r . T h i s e f f e c t i v e l y c h a n g e s t h e o p e r a t i n g p o t e n t i a l o f t h e M I S c a p a c i t o r , i n c r e a s i n g t h e p o t e n t i a l b y a n a m o u n t e q u a l t o a f la t b a n d v o l t a g e shi f t . M a n y e x p e r i m e n t s h a v e b e e n c o n d u c t e d o n M a r c o n i C C D s to i n v e s t i g a t e f l a t b a n d v o l t a g e s h i f t s . H o w e v e r , t h e m a j o r i t y o f t h e m are d o n e o n f r o n t i l l u m i n a t e d d e v i c e s . S i n c e t h e i n s u l a t i n g r e g i o n is b u r i e d i n a b a c k s i d e i l l u m i n a t e d d e v i c e , c o m p a r i s o n s a r e n o t v a l i d . H o w e v e r , C C D 2 6 , a M a r c o n i b a c k s i d e i l l u m i n a t e d d e v i c e w a s t e s t e d f o r flat b a n d v o l t a g e s h i f t s a n d a n i n c r e a s e o f 100 ± 2 0 m V / k r a d ( S i ) w e r e f o u n d ( c f . R o b b i n s 2 0 0 0 ) . T h u s , M O S T w i l l l i k e l y e x p e r i e n c e - 1 0 0 m V v o l t a g e s h i f t o v e r t h e c o u r s e o f o n e y e a r o f o p e r a t i o n . T h i s m a y d e c r e a s e the r e s p o n s i v i t y o f the C C D , b u t i s s u c h a s m a l l s h i f t that e f f e c t s w i l l b e n e g l i g i b l e o v e r t h e f i rs t y e a r o f t h e m i s s i o n ( J o h n s o n , p r i v a t e c o m m u n i c a t i o n ) . I f the m i s s i o n l i f e t i m e is e x t e n d e d , t h e i s s u e o f a f l a t b a n d v o l t a g e s h i f t s h o u l d b e r e v i s i t e d . 8 7 6.1.5 C T E Degradation C T E d e g r a d a t i o n o c c u r s i n r e s p o n s e t o b u l k r a d i a t i o n d a m a g e . I n r e s p o n s e to a d a m a g e d S i la t t i ce , d e e p t r a p p i n g states a r e c r e a t e d , c a p a b l e o f t r a p p i n g e l e c t r o n s . W i t h t i m e t h e y c o n g r e g a t e t o g e t h e r . C T E is d e f i n e d as the f r a c t i o n o f t h e s i g n a l w h e n t r a n s f e r r e d f r o m o n e p i x e l to t h e n e x t . C h a r g e T r a n s f e r I n e f f i c i e n c y ( C T I ) i s the q u a n t i t y ( 1 - C T E ) . It is k n o w n that C T I i n c r e a s e s w i t h s m a l l e r s i g n a l s , a n e f f e c t tha t i s e n h a n c e d b y r a d i a t i o n d a m a g e ( H a r d y 1997) . S i n c e M O S T w i l l o b s e r v e s o m e o f t h e b r i g h t e s t stars i n t h e s k y , i t i s n o t e x p e c t e d that C T I w i l l b e a m a j o r o b s t a c l e . S i n c e C T I i s a r e s u l t o f d i s p l a c e m e n t d a m a g e , i t s c a l e s w i t h n o n - i o n i s i n g e n e r g y l o s s ( N I E L ) , o r t h e a m o u n t o f e n e r g y d e p o s i t e d b y a c h a r g e d p a r t i c l e t h r o u g h a n y p r o c e s s o t h e r t h a n i o n i s a t i o n ( u s u a l l y n u c l e a r i n t e r a c t i o n s ) . R o b b i n s ( 2 0 0 0 ) c o n f i r m s that M E L i s a g o o d f i r s t a p p r o x i m a t i o n . M E L c a n b e c a l c u l a t e d u s i n g a m o d e l d e v e l o p e d b y t h e E u r o p e a n S p a c e R e s e a r c h a n d T e c h n o l o g y C e n t e r a n d a v a i l a b l e o n l i n e t h r o u g h t h e S p a c e E n v i r o n m e n t I n f o r m a t i o n S y s t e m ( S P E N V I S , h t t p : / / w w w . s p e n v i s . o m a . b e / s p e n v i s / ) . F o r t h e M O S T b a s e l i n e o r b i t , M E L i n S i l i c o n as a f u n c t i o n o f s p h e r i c a l A l s h i e l d i n g i s s h o w n i n F i g u r e 6 .3 . 88 1.00E+09 1.00E+06 -1 1 1 0 5 10 Al shielding thickness (mm) Figure 6.3 Non-ionising energy loss as a function of spherical Aluminum shielding thickness. T h e s c a l i n g f a c t o r u s e d to e s t i m a t e C T I f r o m N I E L is u s u a l l y d e t e r m i n e d e x p e r i m e n t a l l y . S i n c e r a d i a t i o n t e s t i n g o f t h e C C D s w a s n o t d o n e as p a r t o f t h i s a n a l y s i s , a n a r b i t r a r y s c a l i n g c o n s t a n t o f 1 x 10" 1 1 g ( S i ) / M e V w a s c h o s e n b a s e d o n D a l e ( 1 9 9 3 ) . It is p r o b a b l y a n o v e r e s t i m a t e o f the a c t u a l f a c t o r a n d h e n c e , t h e r e s u l t s p r e s e n t e d h e r e are e x p e c t e d to b e a n o v e r e s t i m a t i o n o f t h e a c t u a l C T I . T h e s c a l i n g f a c t o r c a n b e r e f i n e d i f r a d i a t i o n t e s t i n g i s e v e r p e r f o r m e d o n the M O S T C C D s . F o r 5 m m o f s p h e r i c a l A l s h i e l d i n g , the N I E L is 1 .97 x 10 M e V / g ( S i ) , a n d the r e l a t i v e d e g r a d a t i o n i n C T E o v e r the c o u r s e o f a 1 y e a r m i s s i o n i n the M O S T b a s e l i n e o r b i t is 1 .97 x 10" 4 . T h u s , a f ter o n e y e a r , t h e l o w e s t m e a s u r e d C T E o f t h e M O S T s c i e n c e g r a d e C C D w i l l b e d e g r a d e d to 0 . 9 9 9 7 9 9 % . 89 6.1.6 Implications for the Photometric Error Budget I n s u m m a r y , t h e f o l l o w i n g ' w o r s t c a s e ' s c e n a r i o m a y o c c u r to t h e M O S T C C D d u r i n g t h e f i r s t y e a r o f o p e r a t i o n s : a) D a r k c u r r e n t i n c r e a s e s to ~ 16 e 7 p i x e l / s ; b ) R T S / D a m a g e d p i x e l s r e m o v e - 6 % o f p i x e l s f r o m f u n c t i o n i n g ; c ) C T E i s d e g r a d e d t o 9 9 . 9 9 9 7 9 9 % ; d ) a n d R e d u c t i o n o f d u t y c y c l e to 8 0 % ( S e c t i o n 4 .4 ) . K u s c h n i g ( 2 0 0 0 ) h a s i n c o r p o r a t e d t h e s e v a l u e s i n t o n u m e r i c a l s i m u l a t i o n s o f t h e M O S T m i c r o s a t e l l i t e . E v e n af ter r a d i a t i o n d a m a g e c o m b i n e d w i t h a l l o t h e r n o i s e s o u r c e s , t h e s i m u l a t i o n s s h o w that M O S T w i l l b e a b l e to o b s e r v e o s c i l l a t i o n s o n t h e o r d e r o f a f e w p p m ( K u s c h n i g , p r i v a t e c o m m u n i c a t i o n 2 0 0 0 ) . 6.2 Single Event Effects (SEEs) S E E s d i f f e r f r o m i o n i s i n g a n d b u l k d a m a g e e f f e c t s b e c a u s e t h e y a r e n o n -c u m u l a t i v e . T h e b r o a d e s t d e f i n i t i o n o f a s i n g l e e v e n t c o v e r s a l l e n e r g e t i c p a r t i c l e i n t e r a c t i o n s w i t h a d e v i c e w h i c h c a u s e a n o b s e r v a b l e e f f e c t . I n g e n e r a l , S E E s are c a u s e d b y a n e n e r g y t r a n s f e r f r o m the c h a r g e d p a r t i c l e to S i l i c o n o r S i l i c o n d i o x i d e i n m i c r o e l e c t r o n i c s ( o r G a l l i u m A r s e n i d e i n s o l a r p a n e l s ) . T h e s e e f f e c t s c a n o c c u r i n a n y e l e c t r o n i c s s y s t e m o r c o m p u t e r d e v i c e a n d a r e n o t l i m i t e d to the C C D . M u l t i - O x i d e -S e m i c o n d u c t o r s ( M O S ) d e v i c e s a r e p a r t i c u l a r l y s e n s i t i v e t o s u c h e f f e c t s , e s p e c i a l l y f i e l d e f f e c t t r a n s i s t o r s ( M O S F E T s ) w h i c h are a c o m m o n c i r c u i t e l e m e n t . O t h e r par ts w h i c h m a y e x p e r i e n c e u p s e t s i n c l u d e t h e d i g i t a l s i g n a l p r o c e s s o r , s o l a r c e l l s , m e m o r y d e v i c e s , l o g i c c i r c u i t s , a n d o t h e r s e n s i t i v e c i r c u i t n o d e s . T h e p r i m a r y e f f e c t s that a c h a r g e d p a r t i c l e c a n c a u s e i n c l u d e ( L a b e l 1997) : • A S i n g l e E v e n t U p s e t ( S E U ) o c c u r s w h e n t h e c h a r g e d p a r t i c l e c a u s e s a b i t f l i p i n a m e m o r y d e v i c e ( a b i n a r y t r a n s i t i o n f r o m 0 to 1 o r v i c e v e r s a ) . • A S i n g l e H a r d E r r o r ( S H E ) o c c u r s w h e n a S E E c a u s e s p e r m a n e n t d a m a g e i n o n e b i t o f m e m o r y . 9 0 • A S i n g l e E v e n t F u n c t i o n a l I n t e r r u p t ( S E F I ) o c c u r s w h e n a S E U c a u s e s a s t r i n g o f c o d e to b e r e a d i n c o r r e c t l y , c a u s i n g t e m p o r a r y i n t e r r u p t i o n o f n o r m a l s y s t e m p e r f o r m a n c e . • A S i n g l e E v e n t L a t c h u p ( S E L ) o c c u r s i n c i r c u i t s w h e n t h e e n e r g y d e p o s i t i o n c a u s e s a b u r s t i n c u r r e n t c a u s i n g a b u r n - o u t i n that c i r c u i t . It i s p o t e n t i a l l y c a t a s t r o p h i c . • A S i n g l e E v e n t B u r n o u t ( S E B ) i s a h i g h l y l o c a l i z e d S E L w h i c h c a u s e s a b u r n o u t i n the d r a i n s o u r c e o f M O S F E T S a s s o c i a t e d w i t h p o w e r g e n e r a t i o n . • T h e M O S F E T s are a l s o s e n s i t i v e to S i n g l e E v e n t G a t e R u p t u r e ( S E G R ) w h e n t h e c h a r g e d p a r t i c l e i n t e r a c t s w i t h a n o x i d e gate l a y e r , c a u s i n g d e s t r u c t i o n a n d p o s s i b l e f a i l u r e . A l t h o u g h it i s p o s s i b l e to c a l c u l a t e t h e n u m b e r o f i n t e r a c t i o n s a d e v i c e w i l l h a v e p e r d a y , o r p e r o r b i t , i t i s n o t p o s s i b l e t o p r e d i c t w h i c h o f t h e a b o v e e f f e c t s it w i l l c a u s e . T h e c a t a s t r o p h i c e f f e c t s are less c o m m o n , o n l y b e c a u s e the v o l u m e s o f m a t e r i a l s e n s i t i v e to that t y p e o f e f f e c t a r e s m a l l . I n t e g r a t e d c i r c u i t s are a l s o s u s c e p t i b l e to S E E s , d e p e n d i n g o n h o w t h e c i r c u i t b o a r d i s m a n u f a c t u r e d . D e v i c e s m a n u f a c t u r e d o n b u l k subst ra te a r e h i g h l y s u s c e p t i b l e to S E U s b e c a u s e c i r c u i t j u n c t i o n s a r e c o n n e c t e d to the s u b s t r a t e ( J o h n s t o n 1996) . I f t h e c i r c u i t i s m a n u f a c t u r e d s u c h that j u n c t i o n i s i s o l a t e d f r o m the s u b s t r a t e s o it c a n n o t b u i l d u p e l e c t r o n s g a t h e r e d w i t h i n t h e subst ra te i t s e l f , t h e n it i s less s e n s i t i v e to t h e r a d i a t i o n e n v i r o n m e n t . T h i s is a c c o m p l i s h e d u s i n g a n e p i t a x i a l l a y e r i n g p r o c e s s to i n s u l a t e the j u n c t i o n s f r o m t h e s u r r o u n d i n g m a t e r i a l . J u n c t i o n s c a n a l s o b e i s o l a t e d i n s p e c i a l o x i d e s to p r e v e n t c h a r g e b u i l d u p . T h e s e latter p r o c e s s e s are m o r e e x p e n s i v e t h a n the f i r s t , b u t w o r t h t h e cos t . W h e t h e r a n S E E h a p p e n s d e p e n d s b o t h o n t h e i n c o m i n g p a r t i c l e ' s e n e r g y a n d o n t h e s u s c e p t i b i l i t y o f t h e d e v i c e it in terac ts w i t h . T h e n u m b e r o f p r o t o n - i n d u c e d u p s e t s i n a d e v i c e c a n b e c a l c u l a t e d u s i n g a s e m i - e m p i r i c a l B e n d e l & P e t e r s e n 2 - p a r a m e t e r m o d e l ( P e t e r s e n 1996) . T h i s m o d e l is a p p r o p r i a t e o n l y f o r S i d e v i c e s . I n a s i m i l a r f a s h i o n to t h e r a d i a t i o n e n v i r o n m e n t m o d e l s , t h e b a s i s o f t h e r e l a t i o n s h i p s w e r e f o u n d a p p l y i n g p a r t i c l e i n t e r a c t i o n t h e o r i e s , b u t the c o e f f i c i e n t s a n d o v e r a l l f o r m u l a e w e r e d e v e l o p e d b y c o m p a r i n g t h e o r y to a c t u a l data . 91 T h e 2 p a r a m e t e r s i n the B e n d e l & P e t e r s e n m o d e l re la te to the c r o s s s e c t i o n f o r p r o t o n u p s e t i n the f o l l o w i n g w a y : p a r a m e t e r s i n M e V , a n d E i s t h e p a r t i c l e ' s e n e r g y i n M e V ( P e t e r s e n 1996) . T h e c r o s s s e c t i o n f o r u p s e t , i n t e g r a t e d w i t h the e n e r g y s p e c t r a o f t h e p r o t o n e n v i r o n m e n t y i e l d s t h e n u m b e r o f u p s e t s , o r S E E rate. T h e t e r m ( B / A ) 1 4 e f f e c t i v e l y d e s c r i b e t h e " l i m i t i n g c r o s s s e c t i o n " o f the d e v i c e : It is t h e v a l u e w h i c h b e s t f i ts the d e v i c e ' s c r o s s s e c t i o n f o r s u s c e p t i b i l i t y to a p a r t i c l e w i t h i n f i n i t e e n e r g y , o r t h e m a x i m u m c r o s s s e c t i o n f o r the d e v i c e . T h e s e p a r a m e t e r s are e x t r e m e l y d e v i c e - d e p e n d e n t . O n a ser ies o f par ts t e s t e d b y S t a p o r et a l . ( 1 9 9 0 ) , b o t h A a n d B r a n g e d f r o m a b o u t 5 - 5 0 M e V . H o w e v e r , f o r a g i v e n d e v i c e , A a n d B a r e w i t h i n a f e w M e V o f e a c h other . I f A w a s l o w , t h e n B w a s a l s o l o w . T h e s t a n d a r d m e t h o d o f t e s t i n g a p a r t f o r its d u r a b i l i t y i n the c o c k t a i l o f p a r t i c l e s a s s o c i a t e d w i t h the o r b i t a l e n v i r o n m e n t i s to p e r f o r m g r o u n d b a s e d tests o n e n g i n e e r i n g g r a d e d e v i c e s . I n o r d e r to f i n d t h e B e n d e l P a r a m e t e r s f o r a g i v e n d e v i c e , the c r o s s s e c t i o n s are f o u n d e x p e r i m e n t a l l y , u s u a l l y b y i r r a d i a t i n g t h e d e v i c e w i t h p r o t o n s at o n l y 1 o r 2 e n e r g i e s (as a c c e l e r a t o r t i m e i s e x p e n s i v e ! ) . F r o m t h e c r o s s s e c t i o n , the d a t a are least s q u a r e f i t to t h e m o d e l a n d A a n d B a r e f o u n d . A l t e r n a t i v e l y , o n e c a n b u y p a r t s that a r e s p e c i f i c a l l y d e s i g n e d f o r s p a c e a n d h a v e a l o w s u s c e p t i b i l i t y to t h e e n v i r o n m e n t . N o g r o u n d - b a s e d t e s t i n g h a s y e t b e e n p e r f o r m e d o n M O S T parts . H e n c e , F i g u r e 6.4 s h o w s the p r o t o n i n d u c e d S E U rate p e r d a y as a f u n c t i o n o f b o t h A a n d B . S i n c e t h e m a j o r i t y o f tests o n v a r i o u s e l e c t r o n i c s s h o w that A ~ B , t h e S E U rate w i l l l i k e l y b e o n the o r d e r o f 1 x 10" 6 S E U / d a y . O n l y r a d i a t i o n t e s t i n g c a n c o n f i r m this . 4 (6 .3 ) V J w h e r e a i s t h e c r o s s s e c t i o n f o r p r o t o n u p s e t s i n c m 2 / b i t , B a n d A a r e t h e B e n d e l 9 2 l.OOE-30 H : i 1 H - • i =4 0 10 20 30 40 50 A parameter (MeV) Figure 6.4 Proton induced single event effect rate as a function of Bendel and Petersen model parameters A and B for the MOST baseline orbit radiation environment. S i n g l e e v e n t e f f e c t s c a n a l s o b e c a u s e d b y h e a v y i o n s . S i n c e t h e n u c l e a r i n t e r a c t i o n s are d i f f e r e n t , a d i f f e r e n t m o d e l i s u s e d to d e s c r i b e t h e n u m b e r o f S E E s t h e y m a y c a u s e . T h o u g h t h e f l u x o f h e a v y i o n s is m u c h l e s s t h a n t h e p r o t o n f l u x , t h e p a r t i c l e s are m u c h m o r e p e n e t r a t i n g t h r o u g h the m a g n e t o s p h e r e a n d s p a c e c r a f t s h i e l d i n g b e c a u s e o f t h e i r h e a v i e r m a s s e s a n d h e n c e , m a y p l a y as l a r g e , i f n o t a l a r g e r r o l e i n t h e n u m b e r o f u p s e t s a s p a c e c r a f t e x p e r i e n c e s . T h i s a n a l y s i s e m p l o y s t h e P i c k e l a n d B l a n f o r d m o d e l f o r h e a v y i o n u p s e t ( P i c k e l 1 9 9 6 ) , s i n c e it i s a l r e a d y i n t e g r a t e d i n t o S P A C E R A D I A T I O N 4 .0 . T h e m o d e l r e q u i r e s k n o w l e d g e o f t h e s e n s i t i v e r e g i o n o f t h e s e m i c o n d u c t o r d e v i c e , a n d t h e f l u x o f t h e i o n s that m a y h i t the s e n s i t i v e a r e a . T h e d e v i c e i s d e s c r i b e d i n t e r m s o f the s e n s i t i v e v o l u m e 93 (dxxdyx dz) and the critical charge (Q). The critical charge is the minimum charge that must be built up in device in order to cause an effect, such as an SEU. The lower the critical charge, the easier it is to cause an upset. Q is given by 6.4: Q = {f}LET(dz) (6.4) where {f} is a function of the material properties of the device, LET is the Linear Energy Transfer (LET) threshold (i.e. the minimum energy which the incident particle must have in order to confer any charge to the device through ionisation), and dz is the depth to which the device is sensitive. {/} for Si is 0.0103, for SiC>2 it is 0.00196, and for GaAs it is 0.0177. Again, radiation testing of the device is needed to determine the LET threshold as well as the sensitive depth. Sensitive volume can be estimated by knowing the structure of the device and making assumptions about its workings (Johnston, 1996). Since radiation testing has not been done on the majority of the MOST electronics, Figure 6.5 shows the upsets/bit/day for the MOST baseline orbit for a range of sensitive volume as a function of critical charge, and two different volume dimensions. From figure 6.5 it is apparent that there is a plateau in the number of upsets a device experiences at low critical charges. This occurs because the device essentially saturates i f exposed to more charge. At the high limit of critical charge, the curves show a very steep drop off. This makes sense, as very few particles will have sufficient energy to actually induce sufficient charge in the device to cause an effect, i f the critical charge exceeds about .01 pC. 9 4 100&08 1.0OBO5 1.00BQ2 l.OOBOl 1.00BO4 Upset OBnj;(pQ Figure 6.5 Heavy ion induced upsets for the MOST baseline orbit for a range of sensitive volume as a function of critical charge. A s t h e s e n s i t i v e v o l u m e o f the d e v i c e i n c r e a s e s , s o d o e s the u p s e t rate. S e n s i t i v e v o l u m e s a r e l i k e l y n o t c u b i c a l as p r e s e n t e d i n F i g u r e 6 .5 , b u t w i l l h a v e s o m e r e c t a n g u l a r s h a p e . T h e d e p t h o f p e n e t r a t i o n o f p a r t i c l e s w i l l d e f i n e the d i r e c t i o n dz, s o r e a l i s t i c a l l y , dz w i l l b e s m a l l e r t h a n t h e s u r f a c e a r e a o f the d e v i c e . T h e h e a v y b l u e l i n e i n d i c a t e s t h i s s c e n a r i o . T h e r e s u l t s d o n o t d i f f e r s i g n i f i c a n t l y f r o m a s y m m e t r i c c u b e w i t h the s a m e s e n s i t i v e v o l u m e . 9 5 E a c h d e v i c e w h i c h is i n t e g r a t e d i n t o t h e M O S T m i c r o s a t e l l i t e s h o u l d b e c o m p a r e d t o t h e a b o v e d i a g r a m . T h e f o l l o w i n g q u e s t i o n s a b o u t the d e v i c e s h o u l d b e a n s w e r e d : • W h a t is t h e s e n s i t i v e v o l u m e o f the d e v i c e ? • W i l l t h e d e v i c e e x p e r i e n c e e x c e s s i v e u p s e t s ? • H o w d o e s the d e v i c e a f f e c t o t h e r s y s t e m s ? T h e latter q u e s t i o n i s p e r h a p s t h e m o s t i m p o r t a n t ( p r o v i d e d the d e v i c e d o e s e x p e r i e n c e u p s e t s ) . I n c o n s i d e r i n g a n y r i s k f a c t o r f o r a s p a c e m i s s i o n , t h e r e i s a c o n s t a n t b a t t l e b e t w e e n c o s t , e f f i c i e n c y ( m a s s b u d g e t , d e l i v e r y s c h e d u l e , e t c . . . ) a n d r i s k . W h e n is t h e r i s k grea t e n o u g h to w a r r a n t s p e n d i n g m o r e m o n e y o n a s p e c i f i c par t? T h u s , the d e v i c e s t h e m s e l v e s a r e n o t t h e o n l y i m p o r t a n t p i e c e o f the p u z z l e . H o w t h e y i n t e r a c t w i t h the o t h e r s y s t e m s , a n d w h a t i m p l i c a t i o n s t h e i r f a i l u r e c o u l d h a v e o n o t h e r s y s t e m s w i l l m i t i g a t e w h e t h e r o r n o t t h e y s h o u l d b e f l o w n . S i n c e c o m p r e h e n s i v e r a d i a t i o n t e s t i n g h a s n o t b e e n d o n e , a n d d e v i c e s p e c i f i c a t i o n s are n o t c u r r e n t l y a v a i l a b l e , it i s n o t p o s s i b l e to p r o v i d e a f u r t h e r e s t i m a t e o f t h e s i n g l e e v e n t rate. O n c e these v a l u e s a r e k n o w n , a c o m p l e t e a s s e s s m e n t o f t h e s i n g l e e f f e c t e f f e c t s c a n b e m a d e . A l l d e v i c e s u t i l i s e d s h o u l d b e r a d i a t i o n h a r d e n e d . 9 6 C h a p t e r 7 : Mi t igat ion of environmental damage T h e r a d i a t i o n e n v i r o n m e n t o f t h e M O S T m i c r o s a t e l l i t e h a s b e e n e v a l u a t e d u s i n g S P A C E R A D I A T I O N 4 .0 , to f i n d y e a r l y i o n i s i n g d o s e s a n d d i s p l a c e m e n t d a m a g e . T h e r a d i a t i o n e n v i r o n m e n t w i l l s l o w l y d e g r a d e t h e C C D d e t e c t o r i n t h e f o l l o w i n g w a y : a) d a r k c u r r e n t w i l l i n c r e a s e b y a b o u t 1 e 7 p i x e l / s o v e r the c o u r s e o f o n e y e a r , b ) C T E w i l l b e d e g r a d e d to 9 9 . 9 9 7 9 9 % f r o m 9 9 . 9 9 9 9 9 % o v e r t h e c o u r s e o f o n e y e a r , c ) 6 % o f p i x e l s w i l l b e d a m a g e s o r d i s p l a y R T S , a n d d ) the d e t e c t o r w i l l e x p e r i e n c e a f l a t - b a n d v o l t a g e s h i f t o n the o r d e r o f a f e w m V p e r y e a r . O t h e r o n - b o a r d m i c r o e l e c t r o n i c s w i l l b e s u s c e p t i b l e to S i n g l e E v e n t E f f e c t s . R a d i a t i o n t e s t i n g o f s e n s i t i v e d e v i c e s a n d c i r c u i t s i s n e e d e d to f u r t h e r q u a n t i f y t h e S E E rate. T h e m a j o r i t y o f t h e s e e f f e c t s o c c u r as t h e sa te l l i te p a s s e s t h r o u g h t h e c h a r g e d p a r t i c l e r i c h r e g i o n o f t h e S A A . T h u s , the c o m b i n e d e f f e c t m a y c a u s e M O S T t o e x p e r i e n c e a t e m p o r a r y l o s s o f d a t a w h i l e i n the d e n s e s t par ts o f t h e S A A . T h i s r e d u c t i o n i n d u t y c y c l e w i l l c rea te a l i a s e s i n the d a t a set. 7.1 Recommendations for the MOST Microsatellite T h e f o l l o w i n g r e c o m m e n d a t i o n s h a v e b e e n m a d e t o m i t i g a t e the e f f e c t s o f the r a d i a t i o n e n v i r o n m e n t o n t h e M O S T m i c r o s a t e l l i t e : a) T h e sa te l l i te n e e d s a m i n i m u m o f 5 m m o f A l s h i e l d i n g . C u r r e n t d e s i g n h a s a b o u t 8 m m o f I n v a r s h i e l d i n g f r o m t h e t e l e s c o p e s t r u c t u r e i t se l f . E x c e s s i v e s h i e l d i n g m a y i n d u c e s e c o n d a r y r e a c t i o n s w h i c h m a y c a u s e as m u c h d a m a g e as p r i m a r y i n t e r a c t i o n s ( D y e r et a l . 1996) . T h u s , s h i e l d i n g s h o u l d n o t b e i n c r e a s e d . b ) C o s m i c r a y h i t s s h o u l d b e r e m o v e d f r o m t h e M O S T d a t a set a n d p i x e l v a l u e s r e p l a c e d b y the m e a n o f t h e s u r r o u n d i n g p i x e l v a l u e s , o r d i s c a r d e d . c ) T h e M O S T d a t a r e d u c t i o n a l g o r i t h m s h o u l d i n c l u d e a filter f o r p i x e l s d i s p l a y i n g R a n d o m T e l e g r a p h S i g n a l i n g ( R T S ) u s i n g t h e a v e r a g e l i f e t i m e i n t h e h i g h s i g n a l 9 7 g e n e r a t i o n state v s . l o w state as the d i s t i n g u i s h i n g s i g n a l o f R T S a n d d i s c a r d a n y p i x e l s s h o w i n g t h i s e f f e c t . d ) T h e b o u n d a r y o f the S A A m e a s u r e d b y t h e F U S E s a t e l l i t e t e a m s h o u l d b e u t i l i z e d t o f i l t e r d a t a t a k e n d u r i n g p a s s a g e t h r o u g h t h e S A A . T h e d a t a t a k e n d u r i n g t h i s t i m e s h o u l d b e a n a l y z e d a n d c o m p a r e d to t h e p r e d i c t i o n s p r e s e n t e d i n t h i s s t u d y to f u r t h e r v a l i d a t e the m o d e l s . e ) T h e sa te l l i te s h o u l d n o t b e l a u n c h e d i n t o a h i g h e r a l t i t u d e o r b i t d u e to the i n c r e a s e d e x p a n s e o f t h e S A A at h i g h e r a l t i t u d e s . 7.2 Other Asteroseismology Missions M O S T w i l l b e f o l l o w e d b y t w o o t h e r s p a c e sa te l l i te m i s s i o n s a l s o a i m i n g t o s t u d y stars t h r o u g h a s t e r o s e i s m o l o g y : C O R O T a n d M O N S . C O R O T h a s a b a s e l i n e o r b i t s i m i l a r to that o f M O S T w i t h a 9 0 0 k m a l t i t u d e a n d 9 9 . 5 ° i n c l i n a t i o n . T h e p r i m a r y d i f f e r e n c e i s that the sa te l l i te w i l l b e i n a n i n e r t i a l o r b i t s o it c o n s t a n t l y f a c e s o n e h a l f o f t h e s k y . T h e M O N S b a s e l i n e o r b i t i s a M o l n i y a t y p e o r b i t , a h i g h l y e c c e n t r i c ( E = 0 . 7 4 1 ) o r b i t w i t h a s e m i m a j o r a c c e s s o f 2 6 5 6 0 a n d a n i n c l i n a t i o n o f 6 3 . 4 ° . M O N S w i l l s p e n d a g r e a t d e a l o f its t i m e f a r f r o m t h e E a r t h a n d s o , w i l l h a v e a c c e s s t o a grea t p o r t i o n o f the s k y . H o w e v e r , i t w i l l a l s o b e o u t s i d e o f g e o m a g n e t i c s h i e l d i n g a n d b e v e r y e x p o s e d to S o l a r E n e r g e t i c P a r t i c l e s ( S E P s ) . A c o m p a r i s o n o f t h e d o s e v s . d e p t h c u r v e s f o r t h e t h r e e m i s s i o n s s h o w s that w i t h 5 m m o f s p h e r i c a l A l s h i e l d i n g , M O S T a n d C O R O T w i l l e x p e r i e n c e a b o u t e q u i v a l e n t d o s e s ( F i g u r e 7 .1) . M O N S w i l l n e e d t o s h i e l d s e n s i t i v e c o m p o n e n t s w i t h u p to 10 m m o f A l i n o r d e r to b r i n g d o w n t h e i r c u m u l a t i v e i o n i s i n g d o s e s to a l e v e l s a f e f o r m o s t d e v i c e s . C O R O T h a s a c u r v e s l i g h t l y l o w e r t h a n t h e M O S T d o s e v s . d e p t h c u r v e b e c a u s e the i n c l i n a t i o n o f t h e o r b i t i s s l i g h t l y greater , a n d h e n c e it e x p e r i e n c e s g r e a t e r g e o m a g n e t i c s h i e l d i n g . S i n c e M O S T i s t h e f i r s t o f the t h r e e m i s s i o n s s c h e d u l e d f o r l a u n c h , it w i l l r e a l l y b e t h e test o f c o n c e p t f o r t h e o t h e r t w o m i s s i o n s . E x p e r i e n c e s f a c e d b y t h e M O S T m i c r o s a t e l l i t e s h o u l d b e u s e d b y the o t h e r sa te l l i te t e a m s i n p e r f e c t i n g t h e i r d e s i g n to w i t h s t a n d t h e o r b i t a l e n v i r o n m e n t i n o r d e r to p e r f o r m a s t e r o s e i s m o l o g y . 98 Figure 7.1 Ionising doses for the MOST (red), MONS (blue), and COROT (green) satellite missions as a function of spherical Al shielding thickness. Models are identical, for flight epochs in 2002. 7.3 Future Work Although it has been determined that the radiation environment will not impede the sensitivity of the M O S T detector over the course of the baseline mission lifetime, there are other effects due to the radiation environment which should be considered prior to launch. Spacecraft charging is a common phenomenon. Particles hit the satellite, and buildup in metallic reservoirs, a process known as di-electric charging. If the charge becomes sufficiently high, arcing will occur, and parts of the satellite may be permanently damaged. Radiation testing of sensitive components to experimentally determine the proton upset cross sections and thus, Bendel parameters should be undertaken. If accelerator time is deemed too expensive, then an alternate fixed source (such as Cobalt 6 0) can be 99 used to simulate the radiation environment. Sensitive volumes of all microelectronics should be considered in order to quantify the Single Event Upset rate. In learning from a previous space satellite with Canadian involvement, FUSE, there were many more SEUs than anticipated. In fact, FUSE must uplink on board command sequences after every pass through the SAA. Since MOST will not have access to as complete a network of ground stations as FUSE, a significant attempt to reduce the SEU rate should be made. 100 References: A l p e r t , M . , 2 0 0 0 , F i r e i n t h e S k y : S p a c e w e a t h e r t u r n s g u s t y as s o l a r a c t i v i t y a p p r o a c h e s its p e a k , S c i e n t i f i c A m e r i c a n , J u l y 2 0 0 0 B a d h w a r , G . D . , O ' N e i l l , M . , 1 9 9 6 , G a l a c t i c C o s m i c R a d i a t i o n M o d e l a n d i ts A p p l i c a t i o n s , A d v . S p a c e R e s . , V . 17, N o . 2 , p p . 7 - 1 7 B a i l e y , P . , 1 9 9 3 , R a d i a t i o n D a m a g e E f f e c t s i n E E V C C D s , C C D T e c h n i c a l N o t e 12, E E V l i m i t e d B a r t h , J . , 1 9 9 7 , N S R E C S h o r t C o u r s e : A p p l y i n g C o m p u t e r S i m u l a t i o n T o o l s to R a d i a i o n E f f e c t s P r o b l e m s , 1 9 9 7 I E E E N u c l e a r a n d S p a c e R a d i a t i o n E f f e c t s C o n f e r e n c e B e a u j e a n , R . , B a r z , S . , J o n a t h a l , D . , E n g e , W . , 1 9 9 6 , O n the O r i g i n o f T r a p p e d H e a v y I o n s at L = 1 . 4 - 1 . 6 , A d v . S p a c e R e s . , V . 17, N o . 2 , p p . 1 6 7 - 1 7 0 B u z a s i , D . , C a t a n z a r i t e , J . , L a h e r , R . , C o n r o w , T . , S h u p e , D . , G a u t i e r , T . 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R . , B r o w n s t e i n , B . , D e i t r e i c h , W . , F l u e c k i g e r , E . O . , P e t e r s e n , E X . , S h e a , M . , S m a r t , D . F . , S m i t h , E . C . , 1 9 9 7 , C R E M E 9 6 : A R e v i s i o n o f t h e C o s m i c R a y E f f e c t s o n M i c r o - E l e c t r o n i c s C o d e , I E E E T a n s . N u c l . S c i , V . 18, p . 9 4 9 9 V a n A l l e n , J a m e s A . , 1 9 8 3 , O r i g i n s o f M a g n e t o s p h e r i c P h y s i c s , S m i t h s o n i a n I n s t i t u t i o n P r e s s , W a s h i n g t o n D . C . V e t t e , J . I . , 1 9 6 6 , M o d e l s o f the T r a p p e d R a d i a t i o n E n v i r o n m e n t , V l - 7 , N A S A , W a s h i n g t o n W a l t , M . , 1994 , I n t r o d u c t i o n to G e o m a g n e t i c a l l y T r a p p e d R a d i a t i o n , C a m b r i d g e U n i v e r s i t y P r e s s , C a m b r i d e W a l t , M . , 1 9 9 6 , S o u r c e a n d L o s s P r o c e s s e s f o r R a d i a t i o n B e l t P r o c e s s e s , i n L e m a i r e , J . F . , H e y n d e r i c k x , D . , B a k e r , D . N . ( e d s ) , R a d i a t i o n B e l t s : M o d e l s a n d S t a n d a r d s , G e o p h y s i c a l M o n o g r a p h 9 7 , A m e r i c a n G e o p h y s i c a l U n i o n , W a s h i n g t o n D C 103 W a t s o n , C . J . , D y e r , C . S . , T r u s c o t t , P . R . , P e e r l e s s , C . L . , S i m s , A . J . , B a r t h , J . L . , 1 9 9 8 , T h e L o w E a r t h O r b i t E n v i r o n m e n t O b s e r v e d u s i n g C R E A M a n d C R E D O , A d v a n c e s i n S p a c e R e s e a r c h , V . 2 1 , N o . , 12, p p 1 6 2 1 - 1 6 2 4 104 Appendix A: Selected MOST Target Stars R A hh: m m : ss D E C deg m m : SS R A deg D E C deg Proper M o t i o n R A D E C M a g . V B Solar-Type Stars Procyon 7 39 20.44 5 14 21.22 114.83517 8.5884167 -0.712 -1.029 0.34 0.74 Beta G e m 7 45 21.259 28 1 36.61 116.33858 28.402542 -0.628 -0.071 1.15 2.15 G a m L e o A 10 19 57.2 19 50 37.34 154.98833 31.655583 0.307 -0.152 2.61 3.76 Eta B o o 13 54 41.217 18 24 9.72 208.67174 24.0405 -0.064 -0.363 2.68 3.26 G a m V i r 12 41 41.407 -1 -26 -58.08 190.42253 -7.742 -0.567 0.004 3.65 4.01 Bet Her 16 30 13.465 21 29 23.27 247.5561 28.346958 -0.099 -0.017 2.77 3.71 Bet O p h 17 43 28.398 4 33 54.25 265.86833 12.476042 -0.042 0.159 2.77 3.93 Zet Her 16 41 18.996 31 35 50.87 250.32915 39.961958 -0.552 0.386 2.81 3.46 Eps V i r 13 2 11.454 10 57 32.1 195.54773 24.38375 -0.275 0.017 2.83 3.77 Subdwarf H D 2 2 4 9 30 0 2 7 27 5 44.9 0.5291667 28.437083 0.841 -0.985 5.75 6.42 H D 76932 8 58 43.01 -16 -8 -8.1 134.67921 -18.03375 0.234 0.214 5.86 6.39 R o - A p s H R 1 2 1 7 3 55 16.4 -12 -5 -55.4 58.818333 -13.480833 -0.062 -0.039 6 6.32 gam E q u 21 10 20.251 10 8 0.99 317.58438 12.004125 0.061 -0.14 4.69 4.95 H D 1 7 6 2 32 18 58 46.82 13 54 26.2 284.69508 26.609167 -0.008 -0.044 5.9 6.14 W o l f -Rayets W R 113 18 19 7.22 -11 -37 -58.8 274.78008 -20.495 -0.022 0.015 9.43 9.86 W R 1 2 8 19 48 32.1 8 12 6 297.13375 11.025 10.5 10.51 W R 123 19 3 59 -4 -49 0 285.99583 -16.25 11.27 11.74 105 A p p e n d i x B: O r b i t a l Parameters M O S T B a s e l i n e O r b i t : • A l t i t u t d e : 8 0 0 k m • I n c l i n a t i o n : 9 8 . 6 ° • O r b i t a l P e r i o d : 1.86 h o u r s • D u r a t i o n : 1 o r b i t • D a t e : 1 2 / 0 1 / 2 0 0 0 • S t a r t t i m e : O h O m i n 0 . 0 0 s • M a g n e t i c F i e l d M o d e l : I G R F 1 9 9 5 • O r b i t a l E p o c h : 2 0 0 2 • C o l a t i t u d e o f the d i p o l e p o l e : 1 0 . 4 7 ° • L o n g i t u d e o f the d i p o l e p o l e : - 7 1 . 8 ° • D i p o l e t i l t a n g l e : - 2 5 . 2 ° T I M E (h) L O N . ( ° ) L A T . ( ° ) A L T I T U D E ( k m ) B L 0 2 6 9 . 6 0 8 0 0 0 . 2 1 7 0 3 6 1 .2049 0 . 0 2 2 6 8 . 8 3.5 800 .1 0 . 2 2 7 8 7 3 1 .2336 0 .03 2 6 8 7.1 8 0 0 . 3 0 . 2 4 0 1 6 6 1 .2726 0 .05 2 6 7 . 2 10 .6 8 0 0 . 6 0 . 2 5 3 6 3 4 1 .3236 0 . 0 7 2 6 6 . 4 14.2 801 0 . 2 6 7 9 7 5 1 .3883 0 . 0 8 2 6 5 . 6 17 .7 8 0 1 . 5 0 . 2 8 2 8 7 5 1 .4694 0.1 2 6 4 . 8 2 1 . 3 8 0 2 . 2 0 . 2 9 8 0 2 7 1 .5698 0 .12 2 6 3 . 9 2 4 . 8 8 0 2 . 9 0 . 3 1 3 1 3 6 1 .6939 0 .13 2 6 3 2 8 . 3 8 0 3 . 7 0 . 3 2 7 9 2 3 1 .8472 0 .15 2 6 2 3 1 . 9 8 0 4 . 6 0 . 3 4 2 1 3 1 2 . 0 3 7 6 0 . 1 7 2 6 1 3 5 . 4 8 0 5 . 5 0 . 3 5 5 5 2 1 2 . 2 7 5 0 . 1 8 2 5 9 . 9 3 8 . 9 8 0 6 . 5 0 . 3 6 7 8 7 2 . 5 7 3 9 0.2 2 5 8 . 7 4 2 . 4 8 0 7 . 4 0 . 3 7 8 9 7 3 2 . 9 5 3 9 0 .22 2 5 7 . 4 4 5 . 9 8 0 8 . 4 0 . 3 8 8 6 4 3 3 . 4 4 3 2 0 .23 2 5 6 4 9 . 4 8 0 9 . 4 0 . 3 9 6 7 2 7 4 . 0 8 2 4 0 .25 2 5 4 . 4 5 2 . 8 8 1 0 . 3 0 . 4 0 3 1 1 9 4 . 9 3 1 3 0 . 2 7 2 5 2 . 6 56 .3 8 1 1 . 2 0 . 4 0 7 7 8 6 . 0 7 7 2 0 .28 2 5 0 . 4 5 9 . 7 8 1 2 0 . 4 1 0 7 6 1 7 . 6 4 9 8 0.3 2 4 7 . 9 63 .1 8 1 2 . 7 0 . 4 1 2 2 1 3 9 . 8 3 4 0 .32 2 4 4 . 7 6 6 . 4 8 1 3 . 4 0 . 4 1 2 3 9 2 > 1 0 0 .33 2 4 0 . 6 6 9 . 7 8 1 3 . 9 0 . 4 1 1 6 4 6 > 1 0 0 .35 2 3 5 . 2 7 2 . 8 8 1 4 . 3 0 . 4 1 0 3 8 8 > 1 0 0 . 3 7 2 2 7 . 7 7 5 . 8 8 1 4 . 7 0 . 4 0 9 0 5 > 1 0 0 . 3 8 2 1 6 . 7 7 8 . 4 8 1 4 . 8 0 . 4 0 8 0 2 7 > 1 0 0.4 2 0 0 . 5 80 .4 8 1 4 . 9 0 . 4 0 7 6 2 5 > 1 0 0 .42 178 .5 81 .4 8 1 4 . 8 0 . 4 0 8 0 1 5 > 1 0 0 .43 155 81 8 1 4 . 5 0 . 4 0 9 2 0 3 > 1 0 0 .45 136.1 7 9 . 4 8 1 4 . 2 0 . 4 1 1 0 3 4 > 1 0 0 . 4 7 123.1 7 6 . 9 8 1 3 . 6 0 . 4 1 3 2 1 1 0 . 0 8 6 3 0 . 4 8 114 .3 7 4 . 1 8 1 3 0 . 4 1 5 3 3 9 7 . 8 4 5 0.5 108.1 71 8 1 2 . 3 0 . 4 1 6 9 8 5 6 . 2 1 6 1 0 . 5 2 103 .5 6 7 . 8 8 1 1 . 4 0 . 4 1 7 7 2 1 5 . 0 1 9 1 0 .53 100 6 4 . 5 8 1 0 . 4 0 . 4 1 7 1 7 1 4 . 1 2 5 9 0 .55 9 7 . 2 61 .1 8 0 9 . 4 0 . 4 1 5 0 4 3 3 . 4 4 9 2 0 . 5 7 9 4 . 9 5 7 . 7 8 0 8 . 2 0 . 4 1 1 1 4 8 2 . 9 2 8 6 0 . 5 8 9 3 54 .3 8 0 7 0 . 4 0 5 4 0 2 2 . 5 2 3 0 .6 9 1 . 3 5 0 . 8 8 0 5 . 8 0 . 3 9 7 8 2 5 2 . 2 0 3 2 0 .62 8 9 . 8 4 7 . 4 8 0 4 . 6 0 . 3 8 8 5 2 6 1 .9488 0 .63 88 .4 4 3 . 9 8 0 3 . 3 0 . 3 7 7 6 9 3 1 .7452 0 .65 8 7 . 2 4 0 . 4 802 .1 0 . 3 6 5 5 8 1 1 .5811 0 . 6 7 86 .1 3 6 . 9 8 0 0 . 9 0 . 3 5 2 5 0 3 1 .449 0 . 6 8 85 3 3 . 3 7 9 9 . 7 0 . 3 3 8 8 2 7 1 . 3 4 2 7 0 . 7 84 .1 2 9 . 8 7 9 8 . 6 0 . 3 2 4 9 7 6 1 .2576 0 .72 83.1 2 6 . 3 7 9 7 . 5 0 . 3 1 1 4 3 1 1 .1905 0 .73 8 2 . 2 2 2 . 7 7 9 6 . 6 0 . 2 9 8 7 2 2 1 . 1 3 8 7 0 .75 81 .4 19.2 7 9 5 . 8 0 . 2 8 7 4 1 1 1 .1003 0 . 7 7 80 .5 15 .6 7 9 5 . 1 0 . 2 7 8 0 4 7 1 .0739 0 . 7 8 7 9 . 7 12.1 7 9 4 . 5 0 . 2 7 1 1 0 3 1 .0585 0.8 7 8 . 9 8.5 7 9 4 . 1 0 . 2 6 6 8 8 8 1 .0535 0 .82 78 .1 5 7 9 3 . 8 0 . 2 6 5 4 7 9 1 .0586 0 .83 7 7 . 3 1.4 7 9 3 . 7 0 . 2 6 6 6 9 1 .0739 0 .85 7 6 . 5 -2.1 7 9 3 . 7 0 . 2 7 0 0 9 9 1 .1002 0 . 8 7 7 5 . 8 - 5 . 7 7 9 3 . 9 0 . 2 7 5 1 2 4 1 .1382 0 . 8 8 7 5 -9 .2 7 9 4 . 2 0 . 2 8 1 1 2 7 1 .1893 0 .9 7 4 . 2 - 1 2 . 8 7 9 4 . 6 0 . 2 8 7 5 0 4 1 .2553 0 .92 73 .3 -16 .3 7 9 5 . 2 0 . 2 9 3 7 5 7 1 .3383 0 .93 7 2 . 5 - 1 9 . 9 7 9 6 0 . 2 9 9 5 2 1 1 .4412 0 .95 7 1 . 6 - 2 3 . 4 7 9 6 . 8 0 . 3 0 4 5 7 8 1 .5674 0 . 9 7 7 0 . 7 - 2 7 7 9 7 . 8 0 . 3 0 8 8 3 5 1 .7214 0 . 9 8 6 9 . 8 -30 .5 7 9 8 . 8 0 . 3 1 2 3 0 1 1 .9082 1 6 8 . 8 -34 8 0 0 0 . 3 1 5 0 5 8 2 . 1 3 4 7 1.02 6 7 . 7 - 3 7 . 6 801 .1 0 . 3 1 7 2 2 5 2 . 4 0 8 6 107 1.03 6 6 . 6 -41 .1 8 0 2 . 4 0 . 3 1 8 9 4 2 . 7 4 0 3 1.05 6 5 . 3 - 4 4 . 6 8 0 3 . 6 0 . 3 2 0 3 3 9 3 . 1 4 1 5 1.07 6 4 -48 .1 8 0 4 . 9 0 . 3 2 1 5 5 2 3 . 6 2 5 8 1.08 6 2 . 4 -51 .5 806 .1 0 . 3 2 2 6 9 9 4 . 2 0 8 4 1.1 6 0 . 7 -55 8 0 7 . 3 0 . 3 2 3 8 8 9 4 . 9 0 2 8 1.12 5 8 . 7 - 5 8 . 4 8 0 8 . 5 0 . 3 2 5 2 2 3 5 . 7 1 6 6 1.13 56 .3 - 6 1 . 8 8 0 9 . 6 0 . 3 2 6 7 8 4 6 . 6 4 1 7 1.15 5 3 . 4 - 6 5 . 2 8 1 0 . 7 0 . 3 2 8 6 2 9 7 . 6 3 8 5 1.17 4 9 . 7 -68 .5 8 1 1 . 6 0 . 3 3 0 7 7 2 8 .618 1.18 4 4 . 9 - 7 1 . 6 8 1 2 . 5 0 . 3 3 3 1 6 9 9 . 4 3 4 2 1.2 3 8 . 3 - 7 4 . 7 8 1 3 . 2 0 . 3 3 5 7 0 7 9 . 9 1 0 6 1.22 2 8 . 7 -77 .5 8 1 3 . 8 0 . 3 3 8 2 0 1 9 . 9 1 3 7 1.23 14 .7 -79 .8 8 1 4 . 3 0 . 3 4 0 4 0 7 9 . 4 3 1 5 1.25 3 5 4 . 6 - 8 1 . 2 8 1 4 . 6 0 . 3 4 2 0 4 4 8 . 5 8 5 5 1 .27 3 3 0 . 9 -81 .3 8 1 4 . 8 0 . 3 4 2 8 3 7 . 5 6 1 9 1.28 3 0 9 . 9 -80 .1 8 1 4 . 9 0 . 3 4 2 5 1 3 6 . 5 2 5 1 1.3 2 9 4 . 8 - 7 7 . 9 8 1 4 . 8 0 . 3 4 0 9 1 3 5 . 5 7 7 2 1.32 2 8 4 . 6 - 7 5 . 2 8 1 4 . 6 0 . 3 3 7 9 4 2 4 . 7 6 1 4 1.33 2 7 7 . 6 - 7 2 . 2 8 1 4 . 3 0 . 3 3 3 6 1 1 4 . 0 8 3 4 1.35 2 7 2 . 5 - 6 9 8 1 3 . 9 0 . 3 2 8 0 3 3 3 . 5 3 0 2 1 .37 2 6 8 . 6 -65 .8 8 1 3 . 3 0 . 3 2 1 3 9 5 3 . 0 8 2 4 1.38 2 6 5 . 6 -62 .4 8 1 2 . 6 0 . 3 1 3 9 2 9 2 . 7 2 0 3 1.4 2 6 3 . 1 - 5 9 8 1 1 . 9 0 . 3 0 5 8 7 7 2 . 4 2 6 6 1.42 2 6 1 . 1 - 5 5 . 6 811 0 . 2 9 7 4 5 9 2 . 1 8 7 5 1.43 2 5 9 . 3 - 5 2 . 2 8 1 0 . 2 0 . 2 8 8 8 5 1.991 . 1.45 2 5 7 . 7 - 4 8 . 7 8 0 9 . 2 0 . 2 8 0 1 7 2 1 .8285 1 .47 2 5 6 . 3 - 4 5 . 2 8 0 8 . 2 0 . 2 7 1 5 0 3 1 .6934 1.48 2 5 5 . 1 - 4 1 . 7 8 0 7 . 3 0 . 2 6 2 8 9 3 1 .5804 1.5 2 5 3 . 9 - 3 8 . 2 8 0 6 . 3 0 . 2 5 4 3 9 6 1 . 4 8 5 6 1.52 2 5 2 . 8 - 3 4 . 7 8 0 5 . 3 0 . 2 4 6 0 9 2 1 .4061 1.53 2 5 1 . 8 -31 .2 8 0 4 . 4 0 . 2 3 8 1 0 9 1 . 3 3 9 6 1.55 2 5 0 . 9 - 2 7 . 6 8 0 3 . 5 0 . 2 3 0 6 3 3 1 .2845 1 .57 2 5 0 -24 .1 8 0 2 . 7 0 . 2 2 3 9 1 .2394 1.58 2 4 9 . 1 - 2 0 . 6 8 0 2 0 . 2 1 8 1 9 3 1 .2035 1.6 2 4 8 . 3 - 1 7 8 0 1 . 4 0 . 2 1 3 8 1 1 .1758 1.62 2 4 7 . 4 -13 .5 8 0 0 . 9 0 . 2 1 1 0 4 1 1 .1558 1.63 2 4 6 . 6 -9 .9 8 0 0 . 5 0 . 2 1 0 1 3 5 1 .1436 1.65 2 4 5 . 8 -6 .4 8 0 0 . 2 0 . 2 1 1 2 7 1 1 . 1 3 8 7 1 .67 2 4 5 -2 .9 8 0 0 . 1 0 . 2 1 4 5 2 1 .1413 1.68 2 4 4 . 3 0 . 7 8 0 0 0 . 2 1 9 8 7 1 1 .1518 1.7 2 4 3 . 5 4 .2 8 0 0 0 . 2 2 7 1 6 2 1.171 1.72 2 4 2 . 7 7.8 8 0 0 . 3 0 . 2 3 6 1 6 6 1 .1995 1.73 2 4 1 . 9 11.3 8 0 0 . 6 0 . 2 4 6 5 9 3 1 .2383 1.75 2 4 1 . 1 14 .9 801 0 . 2 5 8 1 2 4 1 .2888 1 .77 2 4 0 . 2 18 .4 8 0 1 . 6 0 . 2 7 0 4 5 1 1 . 3 5 2 6 1.78 2 3 9 . 4 2 2 8 0 2 . 2 0 . 2 8 3 2 8 9 1 . 4 3 1 9 1.8 2 3 8 . 5 2 5 . 5 803 0 . 2 9 6 3 9 3 1 .5294 1.82 2 3 7 . 6 2 9 8 0 3 . 8 0 . 3 0 9 5 4 7 1 . 6 4 8 9 1.83 2 3 6 . 6 3 2 . 6 8 0 4 . 7 0 . 3 2 2 5 5 1 1 .7953 1.85 2 3 5 . 6 36 .1 8 0 5 . 6 0 . 3 3 5 2 0 9 1 .9746 109 Appendix G: Selected Target Star Dwell Time in the CVZ (Time in weeks) Solar Type Stars: Inclination Altitude Radius Procyon Beta Gam Eta Gam Bet Bet Zet Eps of C V Z Gem Leo A Boo Vir Her Oph Her Vir 8.6 28.4 31.7 24.0 -7.7 28.3 12.5 40.0 24.4 96.0 101.4 10.1 2.8 0.0 0.0 0.0 0.0 0.0 2.3 0.0 0.0 96.2 162.1 12.8 3.6 0.0 0.0 0.0 0.0 0.0 3.2 0.0 0.0 96.4 221.5 14.9 4.3 0.0 0.0 0.0 1.3 0.0 3.9 0.0 0.0 96.6 279.5 16.7 4.8 0.0 0.0 0.0 2.5 0.0 4.5 0.0 0.0 96.8 336.3 18.2 5.3 0.0 0.0 1.7 3.2 0.0 5.0 0.0 1.4 97.0 391.9 19.6 5.7 0.0 0.0 2.8 3.7 0.0 5.5 0.0 2.6 97.2 446.3 20.8 6.0 0.0 0.0 3.6 4.2 0.0 5.8 . o.o 3.4 97.4 499.6 22.0 6.4 1.9 0.0 4.2 4.6 1.9 6.2 0.0 4.0 97.6 551.9 23.0 6.7 2.9 0.0 4.7 5.0 2.9 6.5 0.0 4.6 97.8 603.2 24.0 7.0 3.6 0.7 5.1 5.3 3.6 6.8 0.0 5.0 98.0 653.6 24.9 7.2 4.1 2.3 5.5 5.6 4.2 7.1 0.0 5.4 98.2 703.1 25.7 7.5 4.6 3.1 5.9 5.9 4.6 7.4 0.0 5.8 98.4 751.6 26.5 7.7 5.1 3.7 6.2 6.1 5.1 7.6 0.0 6.1 98.6 799.4 . 27.3 7.9 5.4 4.2 6.5 6.3 5.5 7.8 0.0 6.5 98.8 846.3 28.0 8.1 5.8 4.7 6.8 6.6 5.8 8.1 0.0 6.7 99.0 892.5 28.7 8.3 6.1 5.1 7.1 6.8 6.1 8.3 0.0 7.0 99.2 937.9 29.3 8.5 6.4 5.5 7.3 6.9 6.4 8.4 0.0 7.3 99.4 982.6 29.9 8.7 6.7 5.8 7.6 7.1 6.7 8.6 0.0 7.5 99.6 1026.6 30.5 8.8 7.0 6.1 7.8 7.3 7.0 8.8 0.9 7.7 99.8 1069.9 31.1 9.0 7.2 6.4 8.0 7.4 7.2 9.0 2.2 8.0 100.0 1112.6 31.6 9.2 7.5 6.7 8.2 7.6 7.5 9.1 2.9 8.2 100.2 1154.7 32.1 9.3 7.7 6.9 8.4 7.7 7.7 9.3 3.5 8.4 100.4 1196.1 32.6 9.4 7.9 7.2 8.6 7.9 7.9 9.4 4.0 8.5 100.6 1237.0 33.1 9.6 8.1 7.4 8.8 8.0 8.1 9.6 4.4 8.7 100.8 1277.3 33.6 9.7 8.3 7.6 8.9 8.1 8.3 9.7 4.8 8.9 101.0 1317.0 34.0 9.8 8.5 7.8 9.1 8.2 8.5 9.9 5.2 9.1 101.2 1356.2 34.4 10.0 8.7 8.0 9.3 8.3 8.7 10.0 5.5 9.2 101.4 1394.9 34.9 10.1 8.8 8.2 9.4 8.4 8.8 10.1 5.8 9.4 101.6 1433.1 35.3 10.2 9.0 8.4 9.6 8.5 9.0 10.2 6.1 9.5 101.8 1470.9 35.6 10.3 9.1 8.6 9.7 8.6 9.2 10.3 6.3 9.7 102.0 1508.1 36.0 10.4 9.3 8.8 9.8 8.7 9.3 10.4 6.6 9.8 Metal Poor Subdwarfs: Inclination Altitude HD224930 HD76932 28.4 -18.0 96.0 101.4 0.0 0.0 96.2 162.1 0.0 0.0 96.4 221.5 0.0 0.0 96.6 279.5 0.0 0.0 96.8 336.3 0.0 0.0 97.0 391.9 0.0 0.0 97.2 446.3 0.0 0.0 97.4 499.6 1.8 0.0 97.6 551.9 2.8 0.0 97.8 603.2 3.5 0.0 98.0 653.6 4.1 0.0 98.2 703.1 4.6 0.0 98.4 751.6 5.0 . 0.7 98.6 799.4 5.4 1.7 98.8 846.3 5.8 2.3 99.0 892.5 6.1 2.8 99.2 937.9 6.4 3.2 99.4 982.6 6.7 3.5 99.6 1026.6 7.0 3.8 99.8 1069.9 7.2 4.0 100.0 1112.6 7.4 4.2 100.2 1154.7 7.7 4.5 100.4 1196.1 7.9 4.6 100.6 1237.0 8.1 4.8 100.8 1277.3 8.3 5.0 101.0 1317.0 8.5 5.1 101.2 1356.2 8.6 5.3 101.4 1394.9 8.8 5.4 101.6 1433.1 9.0 5.5 101.8 1470.9 9.1 5.7 102.0 1508.1 9.3 5.8 Wolf Rayet Stars: Inclination Altitude WR113 W R 128 W R 123 -20.5 11.0 -16.3 96.0 101.4 0.0 2.6 0.0 96.2 162.1 0.0 3.4 0.0 96.4 221.5 0.0 4.1 0.0 96.6 279.5 0.0 4.7 0.0 96.8 336.3 0.0 5.1 0.0 97.0 391.9 0.0 5.6 0.0 97.2 446.3 0.0 5.9 0.0 97.4 499.6 0.0 6.3 0.0 97.6 551.9 0.0 6.6 0.0 97.8 603.2 0.0 6.9 0.0 98.0 653.6 0.0 7.2 1.6 98.2 703.1 0.0 7.4 2.3 98.4 751.6 0.0 7.7 2.9 98.6 799.4 0.0 7.9 3.3 98.8 846.3 0.0 8.1 3.6 99.0 892.5 0.0 8.3 3.9 99.2 937.9 0.0 8.5 4.2 99.4 982.6 0.5 8.7 4.5 99.6 1026.6 1.5 8.8 4.7 99.8 1069.9 2.0 9.0 4.9 100.0 1112.6 2.4 9.2 5.1 100.2 1154.7 - 2.8 9.3 5.3 100.4 1196.1 3.1 9.5 5.5 100.6 1237.0 3.3 9.6 5.6 100.8 1277.3 3.5 9.7 5.8 101.0 1317.0 3.7 9.9 5.9 101.2 1356.2 3.9 10.0 6.0 101.4 1394.9 4.1 10.1 6.2 101.6 1433.1 4.2 10.2 6.3 101.8 1470.9 4.4 10.3 6.4 102.0 1508.1 4.5 10.4 6.5 Ro-Ap stars: Inclination Altitude HR 1217 Gam Equ HD176232 -13.5 12.0 26.6 96.0 101.4 0.0 2.4 0.0 96.2 162.1 0.0 3.3 0.0 96.4 221.5 0.0 4.0 0.0 96.6 279.5 0.0 4.6 0.0 96.8 336.3 0.0 5.1 0.0 97.0 391.9 0.0 5.5 0.0 97.2 446.3 0.7 5.9 2.2 97.4 499.6 2.0 6.2 3.1 97.6 551.9 2.7 6.6 3.8 97.8 603.2 3.2 6.8 4.3 98.0 653.6 3.7 7.1 4.8 98.2 703.1 4.0 7.4 5.2 98.4 751.6 4.4 7.6 5.6 98.6 799.4 4.7 7.9 5.9 98.8 846.3 4.9 8.1 6.3 99.0 892.5 5.2 8.3 6.6 99.2 937.9 5.4 8.5 6.8 99.4 982.6 5.6 8:6 7.1 99.6 1026.6 5.8 8.8 7.3 99.8 1069.9 6.0 9.0 7.6 100.0 1112.6 6.1 9.2 7.8 100.2 1154.7 6.3 9.3 8.0 100.4 1196.1 6.4 9.5 8.2 100.6 1237.0 6.6 9.6 8.4 100.8 1277.3 6.7 9.7 8.6 101.0 1317.0 6.8 9.9 8.8 101.2 1356.2 7.0 10.0 8.9 101.4 1394.9 7.1 10.1 9.1 101.6 1433.1 7.2 10.2 9.2 101.8 1470.9 7.3 10.3 9.4 102.0 1508.1 7.4 10.4 9.5 113 A p p e n d i x D: M a p s of T r a p p e d Protons a n d Electrons in the M O S T Baseline O r b i t 0 0 Figure A - l Positional plot of trapped proton flux >1.00 MeV. The ^ SAA is clearly the only feature of this environment. 1 1 4 Longitude Figure A-2 Positional plot of trapped proton flux > 10 MeV. Longitude Figure A-3 Positional plot of trapped proton flux > 300 MeV. Higher energy protons remain confined to a smaller portion of the radiation belt. 115 Longitude Figure A-4 Positional plot of trapped electron flux > 1.0 MeV. Bands in high and low latitudes are a result of the outer radiation belt penetrating to lower altitude. -180 -120 -60 0 60 120 160 Longitude Figure A-5 Positional plot of trapped electron flux > 5.0 MeV. High-energy electrons are not found in the SAA. 116 Appendix E : Cumulative Doses for the MOST Microsatellite Description of Radiation Models A B F J P W M i s s i o n Duration 3.15E+07 3.15E+07 3.15E+07 3.15E+07 3.15E+07 3.15E+07 Geomagnetospheric Conditions normal normal normal normal normal normal Spacecraft Shielding A l Cyl inder A l Cyl inder A l Cyl inder A l Cyl inder T i Cyl inder A I Cyl inder Thickness (mm) 5 5 5 5 2 8 Inner Radius (mm) 75 75 75 75 47.5 75 Height (mm) 449 449 449 449 33 449 Radial Distance (mm) 0 0 0 0 0 0 A x i a l Distance (mm) 123 123 123 123 0 123 Solar C y c l e Solar M a x Solar M a x Solar M a x Solar M i n Solar M a x Solar M a x Geomagnetic Reference F ie ld IGRF2000 IGRF2000 I G R F I G R F I G R F I G R F E p o c h 2000 2002 0 0 0 0 Solar Proton M o d e l JPL91 JPL91 JPL91 JPL91 JPL91 JPL91 Confidence L e v e l 97% 97% 97% 97% 97% 97% Heavy Ion/Proton Ionising Dose Trapped Protons (rad/yr Si) 369 422 369 503 516 306 Solar Protons (rad/yr Si) 410 410 410 410 964 231 Galactic Cosmic Radiation (rad/yr Si) 1.54 1.54 1.54 3.65 1.58 1.51 Electron Ionising Dose Primary Electrons 177 170 177 103 2620 7.14 Bremmstrahlung 8.79 11.6 8.79 5.31 24.2 8 Total Electron Dose 185.79 181.6 185.79 108 2644.2 15.1 T O T A L I O N I S I N G D O S E 966.33 1015.14 966.33 1024.65 4125.78 553.61 Displacement Damage Trapped Protons (rad/yr Si) 3.30E-01 1.60E-01 3.30E-01 1.94E-01 1.85E-01 1.23E-01 Solar Protons (rad/yr Si) 5.37E-01 5.37E-01 5.37E-01 1.20E-01 2.68E-01 7.01E-02 Galactic Cosmic Radiation (rad/yr Si) 5.13E-04 5.13E-04 5.12E-04 1.20E-03 5.12E-04 5.12E-04 T O T A L D I S P L A C E M E N T D O S E (rad/yr Si) 8.68E-01 6.98E-01 8.68E-01 3.15E-01 4.54E-01 1.94E-01 T O T A L D I S P L A C E M E N T D O S E (1 M e V proton equivalents (protons/cm 2) 8.76E+08 7.05E+08 8.76E+08 3.18E+08 4.58E+08 1.96E+08 117 Doses due to SEP as modelled by the C R E M E code Solar Energetic Particle Model Ordinary Scenario 90% Worst Case Scenario 1972 Scenario Composite Worst Case Scenario Spacecraft Shielding A l Cylinder A l Cylinder A l Cylinder A l Cylinder Thickness (mm) 5 5 5 5 Geomagnetospheric Conditions normal normal normal normal Ionising Dose (rad/day Si) 9.03E-01 5.95 318 348 Displacement Dose (rad/day Si) 2.71E-04 1.75E-03 9.69E-02 1.22E-01 Solar Energetic Particle Model Ordinary Scenario 90% Worst Case Scenario 1972 Scenario Composite Worst Case Scenario Spacecraft Shielding A l Cylinder A l Cylinder A l Cylinder A l Cylinder Thickness (mm) 5 5 5 5 Geomagnetospheric Conditions stormy stormy stormy stormy Ionising Dose (rad/day Si) 1.14 7.55 402 436 Displacement Dose (rad/day Si) 3.42E-04 2.22E-03 1.22E-01 1.50E-01 Solar Energetic Particle Model Ordinary Scenario 90% Worst Case Scenario 1972 Scenario Composite Worst Case Scenario Spacecraft Shielding A l Cylinder A l Cylinder A l Cylinder A l Cylinder Thickness (mm) 5 5 5 5 Geomagnetospheric Conditions worst worst worst worst Ionising Dose (rad/day Si) 4.18 27.7 1460 1550 Displacement Dose (rad/day Si) 1.23E-03 8.03E-03 4.38E-01 5.10E-01 Solar Energetic Particle Model Ordinary Scenario 90% Worst Case Scenario 1972 Scenario Composite Worst Case Scenario Spacecraft Shielding Ti Cylinder Ti Cylinder Ti Cylinder Ti Cylinder Thickness (mm) 2 2 2 2 Geomagnetospheric Conditions normal normal normal normal Ionising Dose (rad/day Si) 2.5 13.7 635 665 Displacement Dose (rad/day Si) 7.07E-04 3.86E-03 1.83E-01 2.08E-01 Solar Energetic Particle Model Ordinary Scenario 90% Worst Case Scenario 1972 Scenario Composite Worst Case Scenario Spacecraft Shielding A l Cylinder A l Cylinder A l Cylinder A l Cylinder Thickness (mm) 8 8 8 8 Geomagnetospheric normal normal normal normal 118 Conditions Ionising Dose (rad/day Si) 5.68E-01 3.65 199 230 Displacement Dose (rad/day Si) 1.76E-04 1.10E-03 6.35E-02 8.85E-02 119 Appendix F: Specifications Sheet for Marconi CCD47-20 N o t e : T h i s is the s p e c i f i c a t i o n s s h e e t f o r t h e c o m m e r c i a l o f f - t h e - s h e l f m o d e l . T h e M O S T C C D is c u s t o m d e s i g n e d as w e e l as c u s t o m p a c k a g e d s o the s p e c i f i c a t i o n s f o u n d h e r e m a y n o t b e r e p r e s e n t a t i v e o f t h e M O S T C C D . F o r d e t a i l s o n t h e M O S T C C D see S e c t i o n 1.3.1. 1 1Q 1 2 0 FEATURES • 1024 by 1024 1:1 Image Format • Image Area 13.3 x 13.3 mm • Frame Transfer Operation • 13 |im Square Pixels • Symmetrical Anti-static Gate Protection • Very Low Noise Output Amplifiers • Gated Dump Drain on Output Register • 100% Active Area EEV APPLICATIONS • Spectroscopy • Scientific Imaging • Star Tracking • Medical Imaging INTRODUCTION This version of the CCD47-20 is a front-face illuminated, frame transfer CCD sensor with high performance low noise output amplifiers, suitable for use in slow-scan imaging systems. The image area contains a full 1024 by 1024 pixels which are 13 nm square. The output register is split, allowing either or both of the two output amplifiers to be employed, and is provided with a drain and control gate for charge dump purposes. In common with all EEV CCD Sensors, the CCD47-20 is available with a fibre-optic window or taper, a UV coating or a phosphor coating for X-ray detection. Other variants of the CCD47-20 include IMO, back-thinned and full-frame devices. Designers are advised to consult EEV should they be considering using CCD sensors in abnormal environments or if they require customised packaging. C C D 4 7 - 2 0 H i g h P e r f o r m a n c e C C D S e n s o r TYPICAL PERFORMANCE Maximum readout frequency 5 MHz Output responsivity 4.5 n V / e ~ Peak signal 120 ke~/pixel Dynamic range (at 20 kHz) . . . ~ 6 0 000:1 Spectral range 4 0 0 - 1100 nm Readout noise (at 20 kHz) 2.0 e~ rms QEat 700nm 45 % GENERAL DATA Format Image area 13.3x13.3 mm Active pixels (H) 1024 (V) 1024 Pixel size 13 x 13 nm Storage area 13.3 x 13.3 mm Pixels (H) 1024 (V) 1024 Additional pixels are provided in both the image and storage areas for dark reference and over-scanning purposes. Number of output amplifiers 2 Weight (approx, no window) 7.5 g P a c k a g e Package size 22.7 x 42.0 mm Number of pins 32 Inter-pin spacing 2.54 mm Window material quartz or removable glass Type ceramic DIL array EEV Limited, Waterhouse Lane, Chelmsford, Essex CM1 2QU England Telephone: + 44 (011245 493493 Facsimile: +44 (011245 492492 e-mail: info@eev.com Internet: wwweev . com Holding Company: The General Electric Company, p.I.e. A member of the Marconi Electro-Optics Group. EEV, Inc. 4 Westchester Plaza, PO Box 1482, Elmsford, NY10523-1482 USA Telephone: (914) 592-6050 Facsimile: (914) 682-8922 e-mail: info@eevinc.com ©1998 EEV Limited A1A-CCD47-20 Issue 4, December 1998 411Z4664 I 2-1 PERFORMANCE Min Typical Max Peak charge storage (see note 1) 80k 120k - e /pixel Peak output voltage (no binning) - 540 - mV Dark signal at 293 K (see notes 2 and 3) - 10k 20k e~ /pixel Is Dynamic range (see note 4) - 60000 -Charge transfer efficiency (see note 5): parallel serial - 99.9999 99.9993 - % % Output amplifier responsivity (see note 3) 3.0 4.5 6.0 nV / e ~ Readout noise at 243 K (see notes 3 and 6): grade 0 and 1 grade 2 - 2.0 3.0 4.0 6.0 rms e~/pixel rms e~/pixel Maximum readout frequency (see note 7) - 5.0 - MHz Response non-uniformity (std. deviation) - 3 10 % of mean Dark signal non-uniformity (std. deviation) (see notes 3 and 8) _ 1000 2000 e~/pixel/s ELECTRICAL INTERFACE CHARACTERISTICS Electrode capacitances (measured at mid-clock level) Min Typical Max S0/S0 interphase - 3.5 - nF 10/10 interphase - 3.5 - nF 10/SS and S0/SS - 4.5 - nF R0/R0 interphase - 40 - pF R0/(SS + DG + OD1 - 60 - pF 0R/SS - 10 - pF Output impedance (at typ. operating condition) - 300 - n NOTES 1. Signal level at which resolution begins to degrade. 2. Measured between 233 and 253 K and V s s +9.0 V. Dark signal at any temperature T (kelvin) may be estimated from: Q d /Q d 0 = l 22T 3 e - 6 4 0 0 / T where Q d 0 is the dark signal at T = 293 K (20 °C). 3. Test carried out at EEV on all sensors. 4. Dynamic range is the ratio of readout noise to full well capacity measured at 243 K and 20 kHz readout speed. 5. CCD characterisation measurements made using charge generated by X-ray photons of known energy. 6. Measured using a dual-slope integrator technique (i.e. correlated double sampling) with a 20 us integration period. 7. Readout at speeds in excess of 5 MHz into a 15 pF load can be achieved but performance to the parameters given cannot be guaranteed. 8. Measured between 233 and 253 K, excluding white defects. BLEMISH SPECIFICATION Traps Pixels where charge is temporarily held. Traps are counted if they have a capacity greater than 200 e" at 243 K. Slipped columns Are counted if they have an amplitude greater than 200 e _ . Black spots Are counted when they have a signal level of less than 90% of the local mean at a signal level of approximately half full-well. White spots Are counted when they have a genera-tionrate 25 times the specified maximum dark signal generation rate (measured between 233 and 253 K). The amplitude of white spots will vary in the same manner as dark current, i.e.: Qc/Qdo = i 22T 3 e - 6 4 0 0 / T White column A column which contains at least 21 white defects. Black column A column which contains at least 21 black defects. GRADE 0 1 2 Column defects: black or slipped 0 2 6 white 0 0 0 Black spots 15 25 100 Traps >200e~ 1 2 5 White spots 20 30 50 Grade 5 Devices which are fully functioning, with image quality below that of grade 2, and which may not meet all other performance parameters. Minimum separation between adjacent black columns 50 pixels Note The effect of temperature on defects is that traps will be observed less at higher temperatures but more may appear below 233 K. The amplitude of white spots and columns will decrease rapidly with temperature. CCD47-20, page 2 ©1998 EEV Limited 12Z TYPICAL OUTPUT CIRCUIT NOISE (Measured using clamp and sample) V S S = 9 V VRQ = 18 V Voo = 29 V TYPICAL SPECTRAL RESPONSE (No window) 5 0 h 500 600 WAVELENGTH (nm) TYPICAL VARIATION OF DARK SIGNAL WITH SUBSTRATE VOLTAGE (Two 1 0 phases held low) 60 50 40 " 20 7509 \ V | TYPICAL RANGE| 0 1 2 3 4 6 6 7 . 8 9 10 11 SUBSTRATE VOLTAGE V s s (V) © 1 9 9 8 EEV Limited CCD47-20, page 3 TYPICAL VARIATION OF DARK CURRENT WITH TEMPERATURE PACKAGE TEMPERATURE ("Cl DEVICE SCHEMATIC 3 DARK REFERENCE ROWS SS 1 O ABD 2 0 R 0 1 L 16 O 0 1 7 R01R 8 BLANK ELEMENTS 8 BLANK ELEMENTS CCD47-20, page 4 ©1998 EEV Limited CONNECTIONS, TYPICAL V O L T A G E S A N D A B S O L U T E M A X I M U M RATINGS PULSE AMPLITUDE OR DC LEVEL (V) (See note 9) MAXIMUM RATINGS PIN REF DESCRIPTION Min Typical Max with respect to V s s 1 SS Substrate 0 9 10 -2 ABD Anti-blooming drain (see note 10) VoD -0.3 to +25 V 3 I 0 3 Image area clock 8 12 15 ±20V 4 I02 Image area clock 8 12 15 ±20 V 5 101 Image area clock 8 12 15 ±20 V 6 SS Substrate 0 9 10 -7 OG Output gate 1 3 5 ±20 V 8 RDL Reset transistor drain (left amplifier) 15 17 19 -0.3 to +25 V 9 - No connection - -10 OSL Output transistor source (left amplifier) see note 11 -0.3 to +25 V 11 ODL Output transistor drain (left amplifier) 27 29 31 -0.3 to +35 V 12 SS Substrate 0 9 10 -13 0RL Output reset pulse (left amplifier) 8 12 15 ±20 V 14 R 0 3 L Output register clock (left section) 8 10 15 ±20 V 15 R 0 2 L Output register clock (left section) 8 10 15 ±20 V 16 R01L Output register clock (left section) 8 10 15 ±20 V 17 R01R Output register clock (right section) 8 10 15 ±20 V 18 R 0 2 R Output register clock (right section) 8 10 15 ±20 V 19 R 0 3 R Output register clock (right section) 8 10 15 ±20 V 20 0RR Output reset pulse (right amplifier) 8 12 15 ±20 V 21 SS Substrate 0 9 10 -22 ODR Output transistor drain (right amplifier) 27 29 31 -0.3 to +35 V 23 OSR Output transistor source (right amplifier) see note 11 -0.3 to +25 V 24 - No connection - -25 RDR Reset transistor drain (right amplifier) 15 17 19 -0.3 to +25 V •26 DG Dump gate (see note 12) 0 ±20 V 27 SS Substrate 0 9 10 -28 S01 Storage area clock 8 12 15 ±20 V 29 S02 Storage area clock 8 12 15 ±20 V 30 S 0 3 Storage area clock 8 12 15 ±20 V-31 ABG Anti-blooming gate 0 0 5 ±20 V 32 SS Substrate 0 9 10 -Maximum voltages between pairs of pins: pin 10 (OSL) to pin 11 (ODL) ±15 V pin 22 (ODR) to pin 23 (OSR) ±15 V Maximum output transistor current 10 mA NOTES 9. Readout register clock pulse low levels +1 V; other clock low levels 0±0.5 V. 10. Drain not incorporated, but bias is still necessary. 11. 3 to 5 V below OD. Connect to ground using a 2 to 5 mA current source or appropriate load resistor (typically 5 to 10 kQ). 12. Non-charge dumping level shown. For operation in charge dumping mode, DG should be pulsed to 12 ± 2 V. 13. All devices will operate at the typical values given. However, some adjustment within the minimum to maximum range may be required for to optimise performance for critical applications. It should be noted that conditions for optimum performance may differ from device to device. 14. With the R 0 connections shown, the device will operate through the left hand output only. In order to operate from both outputs R0KR) and R02(R) should be reversed. © 1 9 9 8 EEV Limited CCD47-20, page 5 25 FRAME TRANSFER TIMING DIAGRAM C H A R G E COLLECTION PERIOD 101 102 103 J U T 77' J U L 77. 77--77-.a -1 1033 C Y C L E S ~77 111 ^ UU 77 77 -WJUL^ UI 77 74. "77 H i .77 JUL 77 . a 77" - I U juir 77 umj ^ Lru|irj— 7 7 m i ^  > 1028 C Y C L E S S 0 2 S 0 3 R 0 1 R 0 2 JUL 77 JLMWJUIpLL-77 J l # U L #JUL177JLU # J i l l SEE DETAIL OF LINE T R A N S F E R F R A M E T R A N S F E R PERIOD R 0 3 T T L 3 7 7 U L U L [ J L p ^ ' 3^nnu^Lii|jiijiji^" 377 ^ ^ D WT7 •>1 LINE TIME Vr Hr Hl fr T j u ^ n n n r j ^ UL n n ^ n n n n ^ . .ii. •77 LL 77 u u 7 7 u u u u 7 7 -77 77-SEE DETAIL OF O U T P U T CLOCKING R E A D O U T PERIOD DETAIL OF LINE TRANSFER (For output from a single amplifier) S 0 1 S 0 2 S 0 3 \ V 3 T , — J - t o i - t d r l • t d i r -R 0 2 R 0 3 0R • U L / U U - A A A / J U L A 1 ± U U l A A 1 A A J A A A _ L U U L CCD47-20, page 6 (©1998 EEV Limited DETAIL OF VERTICAL LINE TRANSFER (Single line dump) S01 - • S02 S03 R01 R 0 2 R03 X-J DG - -END OF PREVIOUS LINE READOUT LINE TRANSFER INTO REGISTER \ J DUMP SINGLE LINE FROM REGISTER TO DUMP DRAIN LINE TRANSFER INTO REGISTER \J\J\ r\j\. _ n _ . START OF LINE READOUT DETAIL OF VERTICAL LINE TRANSFER (Multiple line dump) S 0 1 S 0 2 S03 R01 -R02 R 0 3 0R . J U .JL END OF PREVIOUS LINE READOUT 1ST LINE I 2ND LINE 3RD LINE A I A / DUMP MULTIPLE LINE FROM REGISTER TO DUMP DRAIN CLEAR READOUT REGISTER LINE TRANSFER INTO REGISTER \J\J\ START OF LINE READOUT ©1998 EEV Limited CCD47-20, page 7 DETAIL OF OUTPUT CLOCKING R01 R02 R03 0 R OS V RESET FEEDTHROUGH OUTPUT VALID A SIGNAL OUTPUT I2T LINE OUTPUT FORMAT 15 DARK REFERENCE RECOMMENDED D.C. CLAMP TIME I 1024 ACTIVE OUTPUTS = Partially shielded transition elements 15 DARK REFERENCE 7S12 8 BLANK I I I I I I I I CLOCK TIMING REQUIREMENTS Symbol Description Min Typical Max Ti Image clock period 2 5 see note 15 US ••wt Image clock pulse width 1 2.5 see note 15 US tri Image clock pulse rise time (10 to 90%) 0.1 0.5 0.2T us tfi Image clock pulse fall time (10 to 90%) t„ 0.5 0.2T us *oi Image clock pulse overlap (t,i+t f|)/2 0.5 0.2T US tdir Delay time, S0 stop to R0 start 1 2 see note 15 us 'dri Delay time, R0 stop to S0 start 1 1 see note 15 us T r Output register clock cycle period 200 1000 see note 15 ns trr Clock pulse rise time (10 to 90%) 50 0.1Tr 0.3Tr ns tfr Clock pulse fall time (10 to 90%) t „ 0.1T, 0.3Tr ns tor Clock pulse overlap 20 0.5trr 0.1Tr ns W Reset pulse width 30 0.1 TR 0.3Tr ns trx. tfx Reset pulse rise and fall times 0.2twx 0.5trr 0.1Tr ns 'dx Delay time, 0R low to R03 low 30 0.5Tr 0.8Tr ns NOTES 15. No maximum other than that necessary to achieve an acceptable dark signal at the longer readout times. 16. To minimise dark current, two of the 10 clocks should be held low during integration. 10 timing requirements are identical to S 0 (as shown above). CCD47-20, page 8 £51998 EEV Limited OUTPUT CIRCUIT 12$ RD Q 0R 0 S02 (SEE NOTE 17) OD 0 Q R03 OG I I1 •A ss ss OS OUTPUT EXTERNAL LOAD (SEE NOTE 18) T 0 V NOTES 17. The amplifier has a DC restoration circuit which is internally activated whenever S 02 is high. 18. Not critical; can be a 2 to 5 mA constant current supply or an appropriate load resistor. ©1998 EEV Limited CCD47-20, page 9 \2S\ OUTLINE (All dimensions without limits are nominal) A -H -M-IMAGE AREA PIN 1 INDICATOR RECESSED TEMPORARY COVERGLASS IMAGE PLANE J PITCH -Ref Millimetres A 42.00 ± 0.42 B 22.73 ± 0.26 C 16.60 ± 0.25 D 3.64 ± 0.37 E 22.86 ± 0.25 „ + 0.051 F 0254 „ „ „ - 0.025 G 5.0 + 0.5 H 0.457 ± 0.051 J 2.54 + 0.13 K 38.1 L 1.65 + 0.50 M 13.3 N 13.3 CCD47-20. page 10 ©1998 EEV Limited 130 ORDERING INFORMATION Options include: • Temporary Quartz Window • Permanent Quartz Window • Temporary Glass Window • Permanent Glass Window • Fibre-optic Coupling • UV Coating • X-ray Phosphor Coating For further information on the performance of these and other options, please contact EEV. HANDLING CCD SENSORS CCD sensors, in common with most high performance MOS IC devices, are static sensitive. In certain cases a discharge of static electricity may destroy or irreversibly degrade the device. Accordingly, full antistatic handling precautions should be taken whenever using a CCD sensor or module. These include:-• Working at a fully grounded workbench • Operator wearing a grounded wrist strap • All receiving socket pins to be positively grounded • Unattended CCDs should not be left out of their conduct-ing foam or socket. Evidence of incorrect handling will invalidate the warranty. All devices are provided with internal protection circuits to the gate electrodes (pins 3, 4, 5, 7, 13, 14, 15, 16, 17, 18, 19, 20, 26, 28, 29 , 30, 31) but not to the other pins. HIGH ENERGY RADIATION Device parameters may begin to change if subject to greater than 104 rads. This corresponds to: 101 3 of 15 MeV neutrons/cm2 2 x 10 , 3of 1 MeV gamma/cm2 4 x 1011 of ionising particles/cm2 Certain characterisation data are held at EEV. Users planning to use CCDs in a high radiation environment are advised to contact EEV. TEMPERATURE LIMITS Min Typical Max Storage . . . . . . . 73 - 373 K Operating . . . . . . . 73 243 323 K Operation or storage in humid conditions may give rise to ice on the sensor surface on cooling, causing irreversible damage. Maximum device heating/cooling . . . . 5 K/min Whilst EEV has taken care to ensure the accuracy of the information contained herein it accepts no responsibility for the consequences of any use thereof and also reserves the right to change the specification of goods without notice. EEV accepts no liability beyond that set out in its standard conditions of sale in respect of infringement of third party patents arising from the use of tubes or other devices in accordance with information contained herein. © 1 9 9 8 EEV Limited Printed in England CCD47-20, page 11 

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