Coupled Relative Orbit and Attitude Control Augmented by the Geomagnetic Lorentz Propulsions

Abstract

An electrostatically charged spacecraft is subject to the Lorentz force and torque when moving in the geomagnetic field. By active modulation of the surface charge, the induced Lorentz force and torque can be used for orbit and attitude control, respectively. Because of the electromagnetic mechanism, the orbit and attitude motion of such spacecraft are naturally coupled, and the induced Lorentz force and torque are both instantaneously underactuated. Thus, other kinds of actuation are required to render the system fully actuated and controllable. A hybrid control system is then proposed in this paper for Lorentz-augmented spacecraft relative orbit and attitude control. The relative orbit motion is controlled by the combination of the Lorentz force and the thruster-generated control force, and the relative attitude motion is governed by the combination of the Lorentz torque and the magnetic torque. By using the adaptive backstepping control method, a closed-loop control scheme is designed for the hybrid control system to deal with the dynamic coupling, underactuation, unknown external disturbances, and model approximation errors simultaneously. The parameter adaptation laws are derived via the Lyapunov theory to guarantee the stability of the closed-loop system. Optimal distribution laws of the hybrid control inputs are then analytically solved. Finally, numerical examples are simulated in a $J_2$ -perturbed environment to verify the feasibility of the proposed hybrid control system and the validity of the closed-loop control scheme.