Homogeneity-and Sliding Mode-Based Finite-Time Spacecraft Attitude Control Around Asteroids

This article presents a robust finite-time attitude control system for spacecraft orbiting around uniformly rotating asteroids. The zonal and sectorial harmonic coefficients, associated with the gravitational field of the asteroid, are assumed to be unknown. Additionally, it is assumed that a random disturbance torque vector is acting on the spacecraft. The objective is to derive a control law for the roll, pitch and yaw angle trajectory control, despite parameter uncertainties and persistent disturbance torque. First, a control law is designed such the closed-loop nominal system becomes a homogeneous system. Therefore, it achieves finite-time attitude control. Then, a second control law is designed based on a sliding mode control (SMC) technique for rejecting the effect of uncertain parameters and the disturbance input. Through the Lyapunov analysis, it is shown that in the closed-loop system, including the combination of the two control laws, the pitch, roll, and yaw angle trajectory errors converge to zero in a finite time. Simulation is done for the attitude control of the spacecraft in prograde and retrograde elliptic orbits around asteroid 433 Eros. The simulated responses confirm precise attitude trajectory control, despite uncertainties in the model parameters and persistent random disturbance torque.