Adaptive super-twisting control for orbiting around irregular shape small bodies with input saturation

Abstract

Orbiting around a small body is challenging due to the extremely irregular gravitational field and the relatively large disturbances. To consider input saturation and reject the uncertainties and disturbances, an adaptive super-twisting (AST) control scheme for orbiting around a small body is proposed, which attenuates the inherent input chattering of sliding mode control and guarantees strong stability and high accuracy. Firstly, the fast terminal sliding mode (FTSM) manifold is improved to avoid singularity and achieve practical finite-time convergence by switching the manifold to a nonsingular sliding mode surface smoothly when the tracking error is near zero. Then, a fast finite-time disturbance observer, whose output is free of switching terms, is designed by virtue of the terminal sliding mode (TSM) control methodology. Finally, an AST controller considering input saturation is developed by a combination of the super-twisting control scheme and the disturbance observer. The stability of the proposed scheme is analyzed via Lyapunov stability theory, and the finite-time convergence of the closed-loop system is proven. Numerical simulations are conducted, and the results demonstrate the effectiveness of the proposed control scheme.