Disturbance observer-based predefined-time sliding mode attitude control for rigid spacecraft

This paper investigates the predefined-time attitude stabilization control of rigid spacecraft under external disturbances. A predefined-time stability criterion is established using a bounded function. A continuous predefined-time disturbance observer is designed to handle unknown disturbances without requiring the known upper bound of the disturbance magnitude. It should be noted that the observer still requires a known upper bound on the time derivative of the disturbance. Based on the observer estimation, a nonsingular terminal sliding mode controller is designed and employs a piecewise continuous function to avoid singularity. The controller ensures practical predefined-time convergence of the system states, which is independent of the initial conditions and can be explicitly specified by the designer. Comparative simulations demonstrate the superior control performance and robustness of the proposed strategy for rigid spacecraft attitude stabilization.