Modified adaptive variable structure control for flexible spacecraft with input nonlinearities

This paper proposes a robust control algorithm for stabilization of a three-stabilized flexible spacecraft in the presence of model uncertainty, external disturbances and control input nonlinearities. The proposed variable structure output feedback controller ensures the global reaching condition of the sliding mode of the spacecraft dynamics system and the control input nonlinearities are explicitly accounted for in the stability analysis. The structure of the controller is independent of the elastic mode dynamics of the spacecraft. Furthermore, a modified adaptation control law is given for the upper bound on the uncertainty to improve the adaptive performances by adding a negative feedback term. Thus a new controller is designed to guarantee the bound-ness of the closed-loop system and can be described as a combination of sliding mode control law and the modification adaptive law. Numerical simulations show that the precise attitude control and vibration suppression can be accomplished using the derived controller for both cases with and without adaptive control.