in on-board computational capability. Hence, the model in the control system design is at best a truncated approximation of the actual vehicle dynamics. A systematic selection of this approximate model is required in order to retain the significant vehicle dynamics in the controller design, to optimize on-board computations and to ensure satisfactory control in spite of the inevitable model errors. Three distinct approaches have been developed in order to systematically select the controller design model (Fig. 3). The models consist of a hinge-connected multi body model to conduct attitude dynamics and control studies, a continuum model to perform parametric studies of control/structure interaction dynamics and a complete flexible multi body model for performance prediction based on a comprehensive description of the vehicle dynamics. Parametric analysis based on these models has revealed properties of vehicle dynamics (such as mode shapes and frequencies) in terms of the structural parameters (Fig. 4). This parametric model has been used to demonstrate the application of system identification techniques to the SPS dynamics and control. A quasi-inertial mode of operation (Figs. 5-7) has been assessed parametrically and the role of damping on the attitude dynamics investigated. Structural deformations and local slopes arising as a result of dynamic load conditions have been obtained and related to the pointing accuracy and transmitting efficiency of the microwave transmission system (Fig. 8). Current efforts are directed toward application of distributed control and shape determination concepts to the collector and antenna models.
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