| description abstract | This paper presents the design of a higher-order sliding-mode control system for the three-axis attitude control of spacecraft using solar-radiation pressure in a finite time. The spacecraft, equipped with four solar plates, is assumed to be orbiting in an elliptic orbit. The nonlinear spacecraft model includes uncertain parameters and external-disturbance moments. The objective is to control the roll-, pitch-, and yaw-angle trajectories of the spacecraft along prescribed reference trajectories using the solar plates. A higher-order sliding-mode control system is designed which consists of (1) a nominal nonlinear finite-time-stabilizing control law designed based on the notion of geometric homogeneity, and (2) a discontinuous sliding-mode control law to attenuate the effect of uncertainties in the model. For the synthesis of this control system, the attitude-angle errors and their first two derivatives are used. It is shown that in the closed-loop system, the attitude error as well as its first and second derivatives converge to the origin in a finite time. Then a high-gain observer is designed to estimate the first and second derivatives of the attitude-tracking error for synthesis, using only attitude-angle measurement. The closed-loop system including the observer achieves a fast recovery of the performance of the state-feedback higher-order sliding-mode control system. Simulation results are presented which show precise attitude control of the satellite, despite uncertainties in the model, using state variable as well as output feedback. | |
