Appointed-time nonsingular sliding mode control of spacecraft attitude stabilization

This paper investigates the appointed-time attitude stabilization problem of a rigid spacecraft under disturbance and parametric uncertainty. A continuous appointed-time sliding mode disturbance observer is presented to observe the synthetical disturbance term. To circumvent the singularity problem in terminal sliding mode control, a new nonsingular appointed-time sliding mode surface is designed by employing the concept of switching control. Based on the observation information deriving from the proposed disturbance observer, an observer-based nonsingular sliding mode control scheme is developed to stabilize the attitude control system within appointed time which is given by the user. And also, the undesired control chattering phenomenon can be attenuated. The appointed-time stability of the controlled attitude system is proved by the Lyapunov criteria. The simulation results show that the proposed attitude stabilization control scheme is valid.