Direct adaptive control of a flexible spacecraft with disturbances and uncertain actuator failures

This paper addresses the design of a new adaptive attitude tracking control strategy for a flexible spacecraft system in the presence of external disturbances and uncertain failures of redundant reaction wheels. The proposed strategy does not depend on the exact model of the spacecraft and can compensate for a more general class of time-varying and state-dependent failures that reaction wheels may undergo in a practical environment. The controller is built around an integrated adaptive approximation based design that accommodates for both system and actuator failure uncertainties. The controller parameter update law is derived to minimise the control prediction error. Unlike most existing actuator failure compensation techniques which are limited to special cases of actuator failures, the proposed controller can compensate for a larger set of actuator failures with time-varying patterns. Closed-loop system stability and tracking performance are proved using Lyapunov stability theory. Parameter jumps caused by abrupt failures are also taken into consideration during the stability proof. A simulation study is performed on a spacecraft with flexible solar array actuated by redundant reaction wheels. The results show the effectiveness and feasibility of the proposed actuator failure compensation controller compared to other controllers from the literature.