Dissipative Compensators for Flexible Spacecraft Control

This paper addresses the problem of controller design for flexible spacecraft. Model-based compensators, which rely on the knowledge of the system parameters to "tune" the state estimator, are first considered. The instability mechanisms resulting from high sensitivity to parameter uncertainties are investigated. Dissipative controllers, which use collocated actuators and sensors, are next considered. Robustness properties of constant-gain dissipative controllers in the presence of unmodeled elastic-mode dynamics, sensor/actuator nonlinearities, and actuator dynamics are summarized. In order to improve the performance without sacrificing robustness, a class of dissipative dynamic compensators is proposed and is shown to retain robust stability in the presence of second-order actuator dynamics if acceleration feedback is employed. Finally, a class of dissipative dynamic controllers is proposed which consists of a low-authority, constant-gain controller and a high-authority dynamic compensator. A procedure for designing an optimal dissipative dynamic compensator is given, which minimizes a quadratic performance criterion. Such compensators offer the promise for better performance while still retaining robust stability.