Disturbance Observer-Based Attitude Tracking Control for Rigid Spacecraft with Fixed-Time Reaching Law

This paper addresses the fixed-time attitude tracking problem for rigid spacecraft under the influence of external disturbances. To achieve this, a new sliding mode control scheme is proposed, incorporating an innovative reaching law and a fixed-time disturbance observer. The proposed reaching law ensures the convergence of the sliding mode function to zero with fewer control parameters. Additionally, the disturbance observer is designed to effectively compensate for external disturbances without requiring prior knowledge of their initial values. The proposed control framework guarantees fixed-time convergence to the desired attitude for the disturbed rigid spacecraft while mitigating the chattering phenomenon. Numerical simulations are performed to demonstrate the effectiveness and robustness of the proposed scheme.