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Effect of solar radiations on the attitude dynamics of gravity oriented satellites Kumar, Krishna

Abstract

Influence of the solar radiations on the attitude dynamics of gravity gradient satellites is examined and a possibility of using the minute solar force to advantage for general attitude control is explored. A simplified preliminary analysis emphasizes the significance of flexibility in this class of problems. As the governing equations of motion with periodic coefficients are highly non-linear, non-autonomous and involve a large number of system variables, the subject is explored, using approximate analytical as well as numerical techniques, in several stages representing an increasing degree of generalization. The first phase deals with the planar attitude dynamics of cylindrical satellites in an arbitrary ecliptic orbit. The approximate closed form solution, obtained using the W.K.B.J, and Harmonic Balance methods, is found to predict the librational response with considerable accuracy for small amplitude motion. The concept of integral manifold has been effectively applied to obtain the stability bounds of the system. Furthermore, analysis conclusively shows that the solar pressure, which, in general, affects the satellite performance adversely can, in conjunction with a suitable controller, achieve librational damping and attitude control. Effectiveness of the controller in a circular orbit is first investigated through several approximate analytical methods, which are found to predict the damping trends quite accurately. This is followed by a comprehensive numerical analysis leading to the control system design data for satellites in an arbitrary orbit. In the next stage, the study is extended to a more general situation of coupled motion. Even for this complex problem, it is possible to obtain approximate analytical solutions suitable for preliminary design purposes. The effect of various parameters on satellite response is studied through the "system plots". The stability charts have been obtained which indicate the bounds of satellite operation for non-tumbling motion. The attention is then focused on the possibility of achieving spatial attitude control through the solar radiation pressure. The study leads to the development of a semi-passive controller capable of imparting a great degree of versatility to communications satellites and space stations of the future. Finally, an attempt has been made to investigate the planar librational dynamics of a satellite with appendages undergoing elastic deformations induced by the differential solar heating. The structural flexibility, in general, adversely affects the librational response and stability.

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