Nonlinear deformation and attitude control for spinning electrodynamic tether systems during spin-up stage

Abstract

This paper studies the non-linear control of a spinning electrodynamic tether system during its spin-up process. The main problem of the spin-up process is that the tether shape may become irregular due to distributed electrodynamic force, which can lead to risks such as entanglement of the deformed tether with end bodies (base spacecraft and sub-satellite). To deal with this problem, a nonlinear control strategy is proposed in this paper for reducing tether deformation and for stabilizing attitude motions of end bodies. Firstly, the tether system is modeled based on the assumption of a flexible tether, and the minimum current for spin-up is given as the basis for open-loop program design. Secondly, considering the underactuation problem of the tether system, a sliding mode controller with an adaptive law is proposed to track spinning motion and stabilize tether deformation by adjusting only electrical current. Thirdly, considering the limit of attitude control moment, a high-gain saturated controller is proposed to stabilize the attitude motions of end bodies. In the end, numerical results validate that under the regulation of the proposed control strategy, tether deformation is reduced to an insignificant level, and attitude motions of end bodies are stabilized around designated orientations.