Post-capture control of a tumbling space debris via tether tension

The Earth orbit is in a serious predicament caused by millions of space debris, and operational spacecraft are facing a risk of collision with those objects. The net capturing method has been considered as one of the most promising method to remove space debris objects. However, a tumbling target has a risk to slide toward the service satellite and collide with it after captured. To avoid this from happening, a control method must be designed for the combined system. This paper first presents the necessity of controlling the combined system right after the net capture. In another respect, the existing configurations of the combined system always include an additional mechanism to de-tumble the target which will dramatically complicate the design. Instead of using an additional mechanism, a novel control strategy is proposed to de-tumble the target only via the tether connecting to the service satellite and the target. Dynamics of the system is analyzed and flexibility of the tether is considered by employing the mass–spring–damper model. The control method includes three control modes to actively control the pose of the service satellite which significantly impacts the tether tension so that the target can be maintained a safe distance to the service satellite. Numerical simulations demonstrate that the proposed control strategy can be utilized to effectively de-tumble the target within a short period of time and mitigate the risk of collision with the service satellite.