DYNAMICS AND CONTROL OF THE SATELLITE POWER SYSTEM S. J. Wang - J. N. Juang - G. Rodriguez Jet Propulsion Laboratory California Institute of Technology - Pasadena, California The SPS is the largest space system conceived to date that appears feasible with reasonable extensions of existing control technology. It represents a class of large platform-like structures (Fig. 1) that are several orders of magnitude larger than any of the other large space systems (multiplepayload platforms, parabolic reflectors, etc.) currently in planning within NASA. The SPS has in common with all large space systems many control problems that are widely recognized within the controls community. These problems include attitude errors due to disturbances, potential instabilities due to truncated modes and other model errors, lack of damping, and inaccurate preflight knowledge of the vehicle dynamics. The qualitative nature of these problems (model errors, concentrated stresses due to large actuator size, etc.) has emerged as a result of studies in the general area of control of large space structures. However, there is a need at this time, to investigate the dynamics and control problems specifically related to the Satellite Power System (SPS), to assess performance of selected control concepts, and to identify and initiate development of advanced control technology that would enhance feasibility and performance of the SPS system. This paper reports on the initial stages of such a study. One of the areas that has been under intense investigation is that of modeling for controller design. This is widely recognized to be a major and as yet unsolved problem in achieving precise control of large space systems (Fig. 2). This problem arises because, to satisfy performance requirements, the control system must have the means for predicting very accurately the vehicle dynamic response. This is done with a dynamical model that constitutes an integral part of the control system design. The resulting performance is critically dependent on the accuracy of this model. Paradoxically, development and onboard implementation of precise large structure models is difficult if not impossible because of the many degrees-of-freedom, nonlinearities, parameter uncertainties, difficulties in pre-flight dynamics testing, and limitations
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