Adaptive Nonsingular Fixed-Time Attitude Stabilization of Uncertain Spacecraft

This paper addresses the problem of adaptive fixed-time attitude stabilization for uncertain rigid spacecraft with inertia uncertainties, external disturbances, actuator saturations, and faults. A nonsingular fixed-time sliding mode surface is constructed so that the settling time of the established surface is independent of the system initial states. By employing an exponential function in the controller design, an adaptive fixed-time control scheme is proposed to shorten the time during which the system states reach the sliding mode surface. With the proposed control method, the information on the bound of the lumped uncertainty is not needed in prior but estimated by the designed update laws. The fixed-time convergence of both the attitude and angular velocity is established, and comparative simulations are presented to illustrate the effectiveness of the proposed control scheme.

I. Introduction

With the development of space technology, higher control requirements are needed in various space flight missions, and the spacecraft attitude stabilization and control become significant for the mission design and achievement [1]. Hence, plenty of relevant research works on the controllers design, including sliding mode control [2], adaptive control [3], inverse optimal control [4], dynamic feedback control [5], etc., are carried out to achieve the satisfactory control performance in the presence of inertia uncertainties and external disturbances. However, the designed controllers in [2]–[5] could only guarantee the asymptotic stability or uniformly ultimate boundedness (UUB) of the spacecraft system as the time goes to infinity.