Iterative disturbance observer design for spacecraft fault-tolerant control with actuator failure

An observer-based fault-tolerant control scheme is developed for the attitude stabilization control of the rigid spacecraft in the presence of constants and time-varying actuator faults as well as external disturbances. The proposed iterative learning observer employs a learning mechanism to estimate the fault torque values combined with external disturbances, furthermore, the sign function and the revise term of angular velocity estimation error used in observer decrease the computing complexity and improve the estimation precision, respectively. The convergence of estimation error of composite disturbance signal consisting of actuator faults torque and external disturbances is guaranteed irrespective of the control torque or the initial attitude of the spacecraft. Some analyses of the proposed scheme are provided and numerical simulation studies are performed to verify the rapid and accurate convergence of estimation error and good robustness to external disturbances.