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UBC Theses and Dissertations

Dynamics and control of orbiting flexible systems : a formulation with applications Ng, Chun-Ki Alfred


A relatively general formulation for studying the nonlinear dynamics and control of spacecraft with interconnected flexible members in a tree-type topology is developed. The distinctive features of the formulation include the following: (i)It is applicable to a large class of present and future spacecraft with flexible beam and plate type appendages, arbitrary in number and orientation. (ii)The members are free to undergo predefined slewing maneuvers to facilitate modelling of sun tracking solar panels and large angle maneuvers of space based robots. (iii)Solar radiation induced thermal deformations of flexible members are incorporated in the study. (iv)The governing equations of motion are highly nonlinear, non autonomous and coupled. They are programmed in a modular fashion to help isolate the effects of flexibility, librational motion, thermal deformations, slewing maneuvers, shifting center of mass, higher modes, initial conditions, etc. The first chapter of the thesis presents a general background to the subject and a brief review of the relevant literature on multibody dynamics. This is followed by the kinematics and kinetics of the problem leading to the Lagrangian equations of motion. The third chapter focuses on methodology and development of the computer code suitable for parametric dynamical study and control. Next, versatility of the general formulation is illustrated through the analysis of five spacecraft configurations of contemporary interest: the next generation of multi-purpose communications spacecraft represented by the INdian SATellite II (INSAT II); the First Element Launch (FEL) and the Permanently Manned Configuration(PMC) of the proposed Space Station Freedom; the Mobile Servicing System (MSS)to be developed by Canada for operation on the Space Station; and the Space Flyer Unit (SFU) to be launched by Japan in mid-nineties. In the FEL study, the attention is directed towards interactions between the librational and vibrational dynamics. During the PMC investigation, effects of the thermal deformation and orbital eccentricity are introduced and the microgravity environment around the station center of mass explored. The MSS study assesses pointing errors arising from in plane and out-of-plane maneuvers of the robotic arms. The SFU represents a challenging con-figuration to assess deployment and retrieval dynamics associated with a solar array. Parameters considered here include symmetry, orientation and duration of the deployment/retrieval maneuvers. Results of the dynamical study clearly shows that, under critical combinations of parameters, the systems can become unstable. Obviously, the next logical step is to explore control strategies to restore equilibrium. To that end, feasibility of the nonlinear control based on the Feedback Linearization Technique (FLT) is explored with reference to the INSAT II and the MSS. Results show the procedure to be quite promising in controlling the INSAT II over a range of disturbances, including the thermal effects. Application of the control to the MSS reduced the pointing error induced by robotic arm maneuvers significantly. The amount of information obtained through a planned parametric analysis of the system dynamics and control is indeed enormous. More significant results are summarized in the concluding chapter together with a few recommendations for future study.

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