Design of Fixed-time Stable Output Feedback Non-singular Fast Terminal Sliding Mode Attitude Control of a Rigid Spacecraft

This paper presents a control method based on disturbance observer for controlling the attitude of spacecraft in the presence of uncertainties and external disturbances, in which both the controller and the observer have fixed-time convergence. Control methods and disturbance observers with fixed-time convergence are a more advanced form of finite time stability theory in which the convergence time does not depend on the initial conditions of the system and is a function of the controller parameters that can be adjusted by the designer of the control system. In the present study, after modeling the dynamics of satellite attitude using the modified Rodriguez parameters (MRP) method and expressing it as the dynamics of second-order nonlinear systems, a non-singular terminal sliding surface with fixed-time convergence has been designed, based on which the required control inputs have been calculated. Also, to compensate for the effects of uncertainties and external disturbances, a disturbance observer of type universally robust exact differentiator (URED), which guarantees fixed-time convergence, has been used to estimate the function of uncertainties and external disturbances and design the compensating control input. Stability has been proven using Lyapunov theory, and the results of the simulation of the proposed method and its comparison with the methods presented in previous valid and related research have been presented, which indicates the very favorable performance of the proposed method in terms of accuracy and speed of tracking the controller and observer.

کلیدواژه ها:

spacecraft attitude control ، output feedback observer ، fixed time stable terminal sliding mode