Super-twisting disturbance observer–based fuzzy adaptive finite-time control for a class of space unmanned systems with time-varying output constraints

In practical flight process, the time-varying disturbances are often encountered by the space unmanned systems, and the attitude outputs of the space unmanned systems are required to stay in the predefined intervals. Moreover, the convergence process of the space unmanned systems has to be achieved in finite time, to complete the given tasks. However, most of the existing results are difficult to be applied to give consideration to the finite-time-convergence, the constrained outputs and the suppression for the time-varying disturbances simultaneously. To address this problem, in this article, we propose a novel fuzzy adaptive finite-time anti-disturbance control scheme for the space unmanned systems. The super-twisting disturbance observer, which possess the robust and finite-time disturbance estimation ability, has been utilized to suppress the time-varying disturbances. The nonlinear signal transformation technique has been introduced, transforming the constrained outputs into a novel unconstrained auxiliary variable, and the output constrained control issue becomes an equivalent bounded control problem. To achieve the finite-time convenience of the closed-loop space unmanned system, the fractional control laws have been designed, and an important lemma has been utilized to design the update laws of the adaptive parameters. Moreover, the fuzzy logic systems have been used to improve the robustness respect to the uncertainties. The contrastive simulation results have been provided, the finite-time control ability of the proposed method and the satisfactory estimation performance of the super-twisting disturbance observer can be observed.