Adaptive variable structure maneuvering control and vibration reduction of three-axis stabilized flexible spacecraft

This paper proposes a robust control algorithm for stabilization of a three-axis.flexible spacecraft in the presence of model uncertainty, external disturbances and control input nonlinearities. This control algorithim is based on variable structure output feedback control design technique that explicitly accounts for the control input nonlinearities in the stability analysis. Asymptotically and exponentially stable design methods are investigated for constructing the controller to stabilized uncertain system with input nonlinearities. Two kinds of the controller are presented that both ensures the global reaching condition of the sliding mode of the spacecraft dynamics system. Moreover, in the sliding mode, the dynamics system under study still bears the insensitivity to the uncertainties and disturbances as the system with linear input. An additional attractive feature of the control method is that the structure of controller is independent of the elastic mode dynamics of the spacecraft since in practice the measurement of flexible modes is not easy or feasible. It is also shown that an adaptive version of the proposed controller is achieved through removing requirements of knowing the bounds of the uncertainties and perturbations in advance. Furthermore, a modified adaptation control law is given to improve the adaptive performances such that a new controller is designed which can guarantee the boundedness of the closed-loop system. Numerical simulations show that the precise attitude and vibration suppression can be accomplished using the derived controller for both cases with and without adaptive control.