Variable structure control for flexible spacecraft with input nonlinearities during attitude maneuver

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. This control algorithm is based on variable structure output feedback control design technique, and explicitly accounts for the control input nonlinearities in the stability analysis. The proposed variable structure output feedback controller ensures the global reaching condition of the sliding mode of the spacecraft dynamics system. An attractive feature of the control method is that the structure of the 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 releasing the limitation of knowing the bounds of the uncertainties and perturbations in advance. Numerical simulations show that the precise attitude control can be accomplished using the derived controller for both cases with and without adaptive control and the amplitude of the vibration mode is more less than 0.001.