Velocity-free fixed-time output feedback attitude tracking control of rigid spacecraft

This paper studies the problem of velocity-free fixed-time attitude tracking control for spacecraft. A new fixed-time sliding mode control method is proposed for the spacecraft attitude tracking control system. And, a novel fixed-time convergent sliding surface is designed based on the fixed-time control theory. In order to estimate the unmeasurable spacecraft information, the fixed-time observer was used to estimate the attitude information of the spacecraft. Combined with the above method, the fixed-time tracking controller is developed to guarantee the attitude tracking error of spacecraft converges to a small region within a fixed time. The fixed-time stability of the closed-loop system is proved based on the Lyapunov theory, and numerical simulations are presented to illustrate the effectiveness and superiority of the controllers.