Finite-time saturated attitude tracking control for rigid spacecraft

This paper investigates the robust finite-time attitude tracking control problem for rigid spacecraft in the presence of the modeling uncertainty, the external disturbance and actuator saturation. Firstly, based on fast non-singular terminal sliding mode (TSM) surface, fast TSM reaching law, and auxiliary system, an basic robust finite-time saturated controller is designed that takes into account model uncertainties and external disturbances with constant upper bound. A modified auxiliary system is proposed to compensate the actuator saturation effect. Secondly, for the situation that the total disturbance of the system has polynomial upper bound, an adaptive control algorithm is used to online estimate the involved unknown parameters, and an adaptive finite-time saturated controller is designed. Lyapunov stability theory is employed to prove the finite-time stability of the proposed controllers. Simulation results show that the attitude tracking control precisions by the two controllers achieve 5×10^-5 and 1×10^-5, respectively, verifying the effectiveness of the proposed controllers.