Fault-tolerant attitude tracking control of combined spacecraft with actuator saturation based on fully-actuated system approach

In this article, the attitude tracking control problem of combined spacecraft actuated by three reaction wheels under actuator fault, actuator saturation, and external disturbance is investigated. Based on the fully-actuated system approach, a new fault-tolerant attitude tracking scheme is developed by incorporating the Nussbaum gain technique, time-delay estimation (TDE) method, and adaptive method. Firstly, the attitude tracking kinematic and dynamic equation with actuator fault and actuator saturation is transformed into a fully-actuated system model, where a smooth function is used to approximate the actuator torque. After estimating the lumped uncertainty which contains actuator fault, inertia uncertainty, and external disturbance by a TDE method, a new control scheme is designed, where Nussbaum gain is introduced to address the time-varying actuator gain arising from actuator saturation, an adaptive law is adopted to suppress the estimation error. Furthermore, the convergence of the attitude tracking error and angular velocity tracking error is strictly proven by Lyapunov method. Simulation results demonstrate the effectiveness of the proposed control method.