Fixed-time observer based fault tolerant attitude control for reusable launch vehicle with actuator faults

This paper focuses on the fault tolerant attitude control problem for the reusable launch vehicle (RLV) with model uncertainties, external disturbances and actuator failures/faults during the reentry phase. First, the kinematics and dynamics of the RLV are presented, and the control-oriented mode subject to actuator malfunction is established. Next, a novel fixed-time observer is designed to estimate the compound disturbances, including failure information and uncertainties. Specifically, the proposed observer can guarantee the estimation errors converging to zero within a settling time, which is independent with the system initial conditions. Based on the proposed observer, a finite-time fault tolerant attitude control scheme is developed based on the nonsingular terminal sliding mode technology, which would improve the reentry attitude tracking performance and ensure the finite-time stability of the closed-loop attitude control system even in presence of the actuator faults. Finally, the effectiveness of the proposed method is demonstrated by numerical simulations.