This paper studies the dynamic and control problems of space tether system (STS) after capturing space debris. The fully integrated system post-capture is referred to as space tether debris-assembly (STDA), while the system comprising the capture device and debris is termed the debris assembly. A significant challenge in stabilizing STS after debris capture lies in the residual angular momentum of the debris, which, if unmitigated, coupled with the relative angular velocity difference between the debris and the tether, can lead to detrimental effects such as tether entanglement and system destabilization. Furthermore, STDA system experiences unknown mass parameter variations that exacerbate control difficulties. To address these challenges, this paper proposes a nonlinear control strategy designed to rapidly stabilize the attitude motion of the end body, despite uncertainties in mass parameters and boundary constraints. A dynamic model of STDA system, encompassing the host spacecraft, tether, capture device, and space debris, is formulated based on Lagrangian equation. This model accounts for the relative attitude motion between the debris-assembly and the tether, as well as the attitude dynamics of the tether itself, thereby enabling an analysis of disturbances arising from unknown mass parameters and collision-induced angular motion. To mitigate these disturbances, a sliding mode disturbance observer is developed to compensate for dynamic uncertainties associated with the space debris’ unknown mass. Furthermore, an error transformation is performed, and a prescribed performance controller is designed to ensure that the system remains within predefined boundaries during stabilization. The effectiveness of the proposed method is validated through numerical simulations.

This study examines the impact of electric solar wind sail (E-sail) parameters on the attitude stability of E-sail's central spacecraft by using a comprehensive rigid-flexible coupling dynamic model. In this model, the nodal position finite element method is used to model the elastic deformation of the tethers through interconnected two-node tensile elements. The attitude dynamics of the central spacecraft is described using a natural coordinate formulation. The rigid-flexible coupling between the central spacecraft and its flexible tethers is established using Lagrange multipliers. Our research reveals the significant influences of parameters such as tether numbers, tether's electric potential, and solar wind velocity on attitude stability. Specifically, solar wind fluctuations and the distribution of electric potential on the main tethers considerably affect the attitude stability of the spacecraft. For consistent management, the angular velocities of the spacecraft must remain at target values. Moreover, the attitude stability of a spacecraft has a pronounced dependence on the geometrical configuration of the E-sail, with axisymmetric E-sails proving to be more stable.

Spinning electrodynamic tether systems (SEDTs) have promising potential for the active removal of space debris, the construction of observation platforms, and the formation of artificial gravity. However, owing to the survivability problem of long tethers, designing collision-avoidance strategies for SEDTs with space debris is an urgent issue. This study focuses on the design of collision-avoidance strategies for SEDTs with an electrodynamic force (Ampere force). The relative distance between the debris and the SEDT is first derived, and then two collision-avoidance strategies are proposed according to the two different cases. When debris collides closer to a lighter subsatellite, a stationary avoidance strategy is proposed to change the spatial position of the subsatellite by adjusting only the angular motion of the tether, which maintains the original orbit of the SEDT. When debris collides closer to a heavier main spacecraft, a comprehensive avoidance strategy is proposed to change the spatial position of the SEDT by slightly modifying the orbital height and changing the tether angular motion simultaneously. The numerical results illustrate that the proposed strategies promptly avoid potential collisions of an SEDT with space debris without significant changes in the orbital parameters of the SEDT.