Robust fixed-time terminal sliding mode fault tolerant control for liquid-filled spacecraft

In this paper, the fixed-time robust fault tolerant control strategy is proposed for attitude maneuver control system of liquid filled spacecraft with unknown external disturbances, uncertain parameters, actuator faults and control input saturation. In the process of dynamic modeling, the liquid fuel sloshing is equivalent to a viscous spherical model, and the coupling dynamic model of spacecraft is deduced by the Lagrangian formulation. In the process of attitude controller design, a fixed time sliding surface manifold is constructed firstly so that the settling time of the surface manifold is independent of system's initial states. Then, an adaptive fixed time sliding mode control law is designed combined with the fixed time control method and adaptive estimation algorithm, in which the adaptive algorithm is used to estimate the unknown upper bound of the lumped disturbances. The proposed control algorithm uses the saturation function to overcome the singularity problem in the terminal sliding mode control method, and it can shorten the convergence time during the system state reach the sliding surface. Lyapunov stability analysis theory proves that the state of closed-loop system converges to small neighborhood of the origin in fixed time. The comparative simulation results show the effectiveness and robustness of the proposed control method. © 2021, Editorial Department of Control Theory & Applications South China University of Technology. All right reserved.