This paper addresses the problem of attitude control of a spacecraft when unknown dead zones of unknown bounds exist at the actuators. A robust adaptive controller with parameter update laws are designed for the spacecraft's attitude and an asymptotically stable tracking performance is mathematically proven based on the proposed design. Numerical simulation results along with the theoretical proof show that the proposed control scheme can successfully stabilize the attitude of the spacecraft with the unknown actuator dead zones.

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This paper addresses sufficient conditions for asymptotic stability of classes of nonlinear switched systems with external disturbances and arbitrarily fast switching signals. It is shown that asymptotic stability of such systems can be guaranteed if each subsystem satisfies certain variants of observability or 0-distinguishability properties. In view of this result, further extensions of LaSalle stability theorem to nonlinear switched systems with arbitrary switching can be obtained based on these properties. Moreover, the main theorems of this paper provide useful tools for achieving asymptotic stability of dynamic systems undergoing Zeno switching.

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