Energy-Efficient Disturbance Observer-Based Attitude Tracking Control With Fixed-Time Convergence for Spacecraft

This article presents an energy-efficient constrained attitude control scheme with fixed-time convergence for spacecraft. Although fixed-time control provides fast convergence of the system trajectories, it requires large control efforts at the beginning of the response that may result in actuator saturation. To deal with this important problem, a nonlinear first-order fixed-time stable system (NFOFTSS) is introduced. It is analytically proved that the problem of large initial control associated with fixed-time control effort is solved without deteriorating the convergence time. Using the NFOFTSS, a sliding-mode-based attitude control for rigid spacecraft is designed. Since the sliding surface contains the attitude variable and angular velocity, the proposed control constrains the sliding surface in order to indirectly improve both the attitude and angular velocity. Moreover, a fixed-time disturbance observer is designed to reconstruct the total uncertainty of the system. Rigorous proof confirms that the closed-loop attitude system is globally fixed-time stable. Simulation results show the efficiency of the proposed control framework compared to the relevant present works.