Abstract: In this article, a time-delay control (TDC) based backstepping attitude control system is developed for a three-axis stabilized satellite with redundant reaction wheels which takes actuator faults into account. More specifically, this proposed controller combines the TDC and the recursive backstepping technique, in which an integral feedback of the attitude is explicitly incorporated to compensate for possible constant torques. With the TDC, unknown actuator faults are estimated by using one-step previous state information and canceled out by the estimated values, so that the fault detection and isolation mechanism is not involved. Lyapunov analysis is employed to show that the resulting closed-loop system is stable, and that the effect of external disturbances and possible uncertainties on the output can also be attenuated by choosing appropriately the design parameters. To study the effectiveness of the corresponding control scheme, traditional methods are also developed and compared for the control system. Both analytical and numerical results are presented to demonstrate the theoretical and practical merits of this approach.

Key words: satellites, fault tolerant control, backstepping, time-delay control, actuator failure