Attitude Stabilization of Spacecrafts Under Actuator Saturation and Partial Loss of Control Effectiveness

A practical solution is presented to the problem of fault tolerant attitude stabilization for a rigid spacecraft by using feedback from attitude orientation only. The attitude system, represented by modified Rodriguez parameters, is considered in the presence of external disturbances, uncertain inertia parameters, and actuator saturation. A low-cost control scheme is developed to compensate for the partial loss of actuator effectiveness fault. The derived controller not only has the capability to protect the control effort from actuator saturation but also guarantees all the signals in the closed-loop system to be uniformly ultimately bounded. Another feature of the approach is that the implementation of the controller does not require any rate sensor to measure angular velocity. An example is included to verify those highly desirable features in comparison with the conventional velocity-free control strategy.