Fixed-time attitude sliding mode fault-tolerant control for liquid-filled spacecraft

The attitude system of liquid sloshing in liquid-filled spacecraft with actuator saturation, actuator failure, and external disturbance is studied. A sliding mode fault-tolerant control strategy based on a disturbance observer is proposed to achieve attitude fixed-time stability. In the process of dynamic modeling, the liquid fuel with large sloshing is equivalent to the motion pulsating ball model, and the dynamic equation of rigid-liquid coupling spacecraft is established. To guarantee that the complete disturbance in the control system can be calculated in a predetermined amount of time, an adaptive fixed-time disturbance observer is initially created during the attitude controller design phase. On this basis, a fixed-time attitude sliding mode fault-tolerant control strategy is designed by using sliding mode control theory. In addition, by introducing the hyperbolic tangent function, the sign function of traditional input saturation is overcome. Despite external disturbances, actuator failure, and actuator saturation, the control technique may rapidly establish high-precision attitude stability of the spacecraft. Finally, the attitude sliding mode fault-tolerant control scheme proposed in this paper is numerically simulated and compared to verify the effectiveness and superiority of the control strategy.