Space debris is positioned as a fatal problem for current and future space missions. Many effective space debris removal methods have been proposed in the past decade, and several techniques have been either tested on the ground or in parabolic flight experiments. Nevertheless, no uncooperative debris has been removed from any orbit until this moment. Therefore, to expand this research field and progressing the development of space debris removal technologies, this paper reviews and compares the existing technologies with past, present, and future methods and missions. Moreover, since one of the critical problems when designing space debris removal solutions is how to transfer the energy between the chaser/de-orbiting kit and target during the first interaction, this paper proposes a novel classification approach, named ET-Class (Energy Transfer Class). This classification approach provides an energy-based perspective to the space debris phenomenon by classifying how existing methods dissipate or store energy during the first contact.

Active debris removal (ADR) is positioned by space agencies as an in-orbit task of great importance for stabilizing the exponential growth of space debris. Most of the already developed capturing systems are designed for large specific cooperative satellites, which leads to expensive one-to-one solutions. This paper proposed a versatile hybrid-compliant mechanism to target a vast range of small uncooperative space debris in low Earth orbit (LEO), enabling a profitable one-to-many solution. The system is custom-built to fit into a CubeSat. It incorporates active (with linear actuators and impedance controller) and passive (with revolute joints) compliance to dissipate the impact energy, ensure sufficient contact time, and successfully help capture a broader range of space debris. A simulation study was conducted to evaluate and validate the necessity of integrating hybrid compliance into the ADR system. This study found the relationships among the debris mass, the system’s stiffness, and the contact time and provided the required data for tuning the impedance controller (IC) gains. This study also demonstrated the importance of hybrid compliance to guarantee the safe and reliable capture of a broader range of space debris.

This paper proposes an adaptive control scheme for capturing uncooperative space debris having uncertain inertial parameters. Debris parameters may be unknown or uncertain due to limited data or changes in orbit due to collisions. To address this challenge, the proposed scheme integrates an inertial parameter identification law with the impedance control strategy of FlexeS (Flexible Capture System). During the pre-capture phase, motion data is utilized to identify the debris’ center of mass (CM), leading to the optimal capture point that minimizes impact moments. During contact, the impedance-controlled actuator(s) is(are) activated while the scheme concurrently provides accurate estimates of the debris mass and inertia, enabling the updating of controller gains and thus ensuring sufficient contact time for successful capture. Hence, the proposed adaptive scheme allows FlexeS to handle the debris parameter uncertainties. The simulation study demonstrates the scheme’s effectiveness and necessity. The performance of the proposed adaptive scheme is compared with a non-adaptive scheme. The results affirm the superiority of the adaptive scheme in achieving successful soft capture of uncooperative debris in the presence of mass and inertia uncertainties and highlight its potential for future space debris mitigation missions.