Spacecraft attitude fault-tolerant control based on iterative learning observer and control allocation

In this paper, an observer-based fault-tolerant control scheme is proposed for the attitude stabilization of rigid spacecraft in the presence of actuator fault, configuration misalignment, input saturation and even external disturbances simultaneously. More specifically, an iterative learning observer is firstly developed to estimate the torque deviation and steer the estimation errors into some small residual sets. And also the detailed derivations of the observer are provided, along with a thorough analysis for the associated ultimate bounded stability and estimation error convergence property. Then, an integral-type sliding mode control law is designed to produce the three-axis virtual control signals with the desired performance for being distributed among the individual actuators. Under this, a robust control allocation algorithm is developed to map the virtual control demand onto individual actuator in an optimal manner, which takes into account the estimation uncertainties and ensures some fault-tolerant ability. The key feature of the proposed strategies is that the whole closed-loop fault tolerant control system can be guaranteed theoretically to be stable by the development of Lyapunov methodology. Numerical simulation results are presented to illustrate and highlight the fine performance benefits obtained using the proposed schemes.