Combined adaptive variable structure and time delay fault tolerant control for spacecraft

Time-delay-control(TDC) based adaptive variable structure control(AVSC) system is designed for spacecraft attitude maneuvers with redundant actuators(thrusters), taking actuator failures, parametric uncertainties and external disturbances into account. More specifically, proposed scheme combines the TDC and AVSC design technique, such that this design does not require the knowledge of the boundedness of the considered uncertainties/disturbances, and only one parameter is required to be updated in the adaptive loop. With the TDC, the unknown actuator faults are estimated by using one-step previous state information and canceled out by the estimated values, such that it does not need a fault detection and isolation mechanism. Lyapunov stability analysis shows that the resulting closed-loop system is proven to be stable and the effect of the external disturbances and possible uncertainties on the output can be attenuated by appropriately choosing the design parameters. Both analytical and numerical results show the theoretical and practical merit of this approach.