An adaptive actuator failure compensation scheme for spacecraft with momentum wheels

An adaptive actuator failure compensation scheme is developed for attitude tracking control of a spacecraft with four reaction momentum wheels, in the presence of unknown spacecraft inertia parameters, nonlinear dynamics of wheel angular momentum and uncertain actuator failures. The proposed scheme employs a composite adaptive control design which incorporates an adaptive backstepping feedback control law and an adaptive feedforward actuator failure compensator whose parameters are adaptive estimates of failure pattern and value parameters. All possible failures can be estimated based on a complete parametrization without explicit failure detection. Based on a new compensation framework, the unknown system parameters can be estimated directly and the additional disturbances introduced by the nonlinear dynamics can be compensated completely, so that the stability of the closed-loop system and asymptotic attitude tracking can be achieved despite the presence of the unknown inertia matrix and uncertain actuator failures. Illustrative simulation results are presented to verify the desired system properties.