Inertia-free fault-tolerant spacecraft attitude tracking using control allocation

The problem of fault-tolerant attitude tracking control for an over-actuated spacecraft in the presence of actuator faults/failures and external disturbances is addressed in this paper. Assuming that information on the inertia and bounds on the disturbances are unknown, a novel fault-tolerant control (FTC) law incorporating on-line control allocation (CA) is developed to handle actuator faults/failures. To improve the robustness of the adaptive law and stop the adaptive gain from increasing, the time-varying dead-zone modification technique is employed in parameter adaptations. It is shown that uniform ultimate boundedness of the tracking errors can be ensured. To illustrate the efficiency of the CA-based FTC strategy, numerical simulations are carried out for a rigid spacecraft under actuator faults and failures.