Fixed-time attitude control for spacecraft without unwinding

This paper investigates a fixed-time anti-unwinding attitude controller for spacecraft. With the use of rotation matrix, unwinding problem, which widely exists in controllers based on quaternion can be dealt with. By means of a fixed- time sliding mode surface, the desired attitude command can be tracked in a fixed time, the bound of which can be estimated without knowing any information of the initial values of system states. Mathematical demonstration and simulation results validate the effectiveness of the controller developed in this paper.