Variable structure output feedback control of a spacecraft under input dead-zone non-linearity

This paper proposes a robust control algorithm for stabilization of a three-axis stabilized flexible spacecraft in the presence of parametric uncertainty, external disturbance, and input dead-zone non-linearity. This control algorithm is based on the variable structure output feedback control (VSOFC) design technique, and explicitly accounts for control input dead-zone non-linearity in the stability analysis. Asymptotically and exponentially stable design methods are investigated for constructing the controller to stabilize the uncertain system. Furthermore, the developed controller is achieved through adaptive VSOFC (AVSOFC) without the limitation of knowing the bounds of uncertainties and perturbations in advance. The AVSOFC law results in substantially simpler stability analysis and improves the overall response. In addition, a modified adaptation control law is presented for the upper bound on the perturbation to improve the adaptive performances such that a new controller is designed that can guarantee the bound of the estimated gains. Numerical simulations show that precise attitude control and vibration suppression can be accomplished using the derived controller for both cases with and without adaptive control.