Conventional tether-net systems deployed from a chaser spacecraft are essentially uncontrolled after ejection, which leads to limited pointing accuracy and a very short capture window. This significantly reduces the probability of a successful capture. To overcome these limitations, this study investigates a tethered space net robot (TSNR) system consisting of a flexible tether-net and four small maneuvering spacecraft that are referred to as TSNRs, each connected to a corner of the tether-net. This study aims to develop a cooperative approach control method that allows a tethered robot system to autonomously track a target debris object without requiring knowledge of its absolute position or velocity. The proposed framework combines vision-based relative state estimation and cooperative control. The position of the debris relative to the spacecraft is estimated using stereo vision constructed from multiple monocular cameras mounted on the spacecraft. The desired formation for the spacecraft surrounding the debris is determined based on the relative positions of the spacecraft and the net center. The optimal rotational orientation of the formation is computed such that the TSNR system configuration approaches an ideal square arrangement. To achieve both debris tracking and inter-spacecraft distance regulation, a control strategy based on the artificial potential-field method is introduced. Potential functions are defined for attraction toward the goal formation and for maintaining appropriate distances between TSNRs, including upper and lower bounds that prevent tether overstretching or collisions between TSNRs. Numerical simulations are conducted to evaluate the effectiveness of the proposed approach. The results demonstrate that the TSNRs can cooperatively deploy a net, maintain a stable formation, and pursue approaching debris while avoiding collisions between them.

This study involved simulations and experiments aimed at assessing the efficacy of a tether net in encapsulating space debris. The tether net was modeled as a spring–mass–damper system considering the influence of aerodynamic and gravitational forces and the occurrence of debris collisions. To examine the influence of collision position and size disparity between the debris and the net on debris capture status, the entanglement nodes of the net were identified. Experiments were conducted to evaluate the wrapping capabilities of the tether net, focusing specifically on debris capture. Subsequently, the results were compared with those of the numerical simulation. In the experiments, radio frequency identification was used to identify the entanglement points of the tether net. Previous studies have indicated that the ideal collision point for capturing debris using a tether net with the debris intended to be captured is located at the center of the net. However, the experimental results of this study revealed that a collision position that is slightly shifted from the center of the tether net is more advantageous for capturing debris in terms of tether net entanglement.