| Summary: | Fast and high-precision attitude control for the rigid spacecraft is important for its broad applications in astronautics. In this paper, we address this problem via continuous nonsingular fixed-time sliding mode control approach. At first, by improving the adding power integral technique, a nonsingular nominal attitude controller is presented to achieve fixed-time convergence of the unperturbed attitude system, which underpins the basics for design of the sliding mode motion and surfaces for the subsequent proposed main results. Then, a fixed-time full-order sliding mode controller with an explicit bound of settling time is proposed to track the desire attitude even in the presence of external disturbances. However, this controller requires the angular acceleration signals which is usually unmeasurable. To this end, an integral sliding mode controller is further presented to achieve fixed-time attitude tracking without using any acceleration information. This proposed integral sliding mode controller can realize second-order sliding mode with rigorous proof of fixed-time convergence. Both the proposed fixed time full-order and integral sliding mode controller are inherent nonsingular and chattering-free. Numerical examples are illustrated to demonstrate the effectiveness of the results given herein in practical scenarios.
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