Composite disturbance observer<bold>-</bold>based adaptive sliding mode fault<bold>-</bold>tolerant attitude control during RLV reentry phase

Aiming at the attitude control of reusable launch vehicle in reentry phase under restrains of parametric uncertainties， external strong disturbances and compound actuator faults， an adaptive sliding mode fault-tolerant control method based on composite disturbance observer （CDO） is proposed. Firstly， the RLV attitude tracking error model considering actuator effectiveness loss and bias faults is established. Then， a cascade and fused CDO is designed to accurately estimate the lumped disturbance. On this basis， a chattering-free adaptive sliding mode control law based on the disturbance compensation strategy is designed， which employs the online adaptive gain to replace the discontinuous switching subject and ensure fixed-time convergence while eliminating chattering. The simulation results show that compared with existing methods， the tracking accuracy， convergence speed and control smoothness are significantly improved by using the proposed scheme which is under fault scenarios with extreme disturbances and verifies its superior fault-tolerant performance and robustness.