A Comparative Mechanical Study of Net-, Tether-, and Robotic-Based Space Debris Capture Systems in Low Earth Orbit

Abstract

The proliferation of space debris in Low Earth Orbit (LEO) has precipitated a critical inflection point in orbital sustainability, necessitating the transition from passive mitigation guidelines to active remediation strategies. While the astrodynamics of rendezvous and phasing are well-understood, the mechanical feasibility of physically capturing non-cooperative, tumbling targets remains the primary engineering bottleneck preventing scalable Active Debris Removal (ADR). This paper presents an exhaustive comparative mechanical analysis of three predominant capture architectures: flexible net-based systems, tethered projectile (harpoon) systems, and rigid robotic grasping mechanisms. The study rigorously examines the dynamic interactions, structural loading requirements, and failure modes inherent to each architecture when interfacing with high-mass, high-inertia targets such as the European Space Agency’s Envisat satellite and the Soviet-era Zenit-2 rocket bodies. Analytical models utilizing discretized mass-spring-damper formulations for flexible tethers and nets, Johnson-Cook constitutive material models for high-strain-rate harpoon impacts, and Hertzian contact theories for robotic grasping are synthesized to evaluate performance boundaries. The analysis reveals that net-based systems offer superior compliance and reduced guidance precision requirements for tumbling targets but suffer from complex, stochastic deployment dynamics and potential entanglement uncertainties. Conversely, robotic manipulators provide deterministic control and rigid capture capability but demand high-bandwidth impedance control to manage contact instability and are severely limited by the target\'s tumbling rate due to actuator saturation limits. Tether-harpoon systems occupy a mechanical middle ground, offering rapid capture with high impulse transfer, yet introducing significant risks of structural fragmentation and recoil dynamics that threaten the chaser spacecraft. Through a systematic trade-off analysis focusing on structural complexity, deployment risk, and post-capture stabilization, this report concludes that no single mechanism is universally optimal; rather, the mechanical selection is strictly governed by the target’s angular momentum vector, structural integrity, and the acceptable risk profile of the mission. The results underscore that effective debris removal systems will ultimately depend on robust mechanical design capable of tolerating substantial dynamic uncertainties rather than conceptual novelty alone.

Introduction

The paper addresses the growing crisis of space debris in Low Earth Orbit (LEO), particularly in densely populated Sun-Synchronous Orbit (600–1000 km), where object density may trigger a self-sustaining collisional cascade known as the Kessler Syndrome. Over 36,000 objects larger than 10 cm are tracked, with millions of smaller fragments posing mission-ending risks. While mitigation efforts aim to prevent new debris, the urgent need is for Active Debris Removal (ADR), targeting massive derelict satellites and rocket bodies (e.g., Envisat and Zenit-2) that serve as primary sources of future fragmentation.

Capturing these large, non-cooperative, tumbling objects presents severe mechanical challenges. They lack docking interfaces, may rotate with significant angular momentum, and have uncertain structural integrity due to long-term environmental degradation. Despite extensive research on orbital mechanics and policy, a major gap exists in detailed mechanical analysis of the capture phase—specifically the transient contact forces, energy dissipation, structural stresses, and failure modes during physical interaction.

The report focuses on the mechanical engineering evaluation of three contact-based ADR technologies: nets, harpoons, and robotic arms. It develops a unified analytical framework comparing force transmission, energy absorption, structural loads, and failure risks. Advanced dynamic models—such as Johnson-Cook penetration (harpoons), Absolute Nodal Coordinate Formulation (nets), and Hertzian contact models (robotics)—are applied to real-world targets (Envisat, Zenit-2) to assess feasibility and design sensitivities.

The mechanical environment in LEO adds complexity: debris objects are free-floating, often tumbling with high rotational kinetic energy, and governed by relative orbital dynamics (Hill-Clohessy-Wiltshire equations). Capture systems must meet four key mechanical requirements: structural robustness, energy dissipation, deployment reliability in vacuum, and post-capture stabilization.

Net-based systems are examined in detail as flexible capture mechanisms that distribute impact forces across multiple nodes, reducing stress concentration. Their performance depends on deployment dynamics, mesh strength, tension control, and avoidance of failure modes such as tearing or entanglement.

Overall, the study emphasizes that the success of ADR missions depends not only on orbital rendezvous but critically on the mechanical feasibility of the capture interaction itself, highlighting the need for rigorous, system-level mechanical analysis to prevent mission failure.

Conclusion

The active removal of space debris is not merely a trajectory problem; it is a profound mechanical engineering challenge characterized by high-energy interactions, uncertain physical properties, and the unforgiving environment of microgravity. This comparative study has highlighted that the \"best\" capture system is heavily context-dependent. Net-based systems excel in capturing large, tumbling, and irregular objects like Envisat due to their inherent mechanical compliance and generous capture envelope, though they face challenges in simulation reliability and post-capture securing. Tether-harpoon systems offer mechanical simplicity and robust towing connections for rocket bodies like Zenit-2 but carry significant risks of debris generation and require precise target characterization. Robotic arms provide the highest level of control and reversibility, making them ideal for servicing or stabilizing widely tumbling objects, yet they are penalized by high mass, complexity, and strict operational limits on target spin rates. Ultimately, effective debris removal architectures will likely evolve into hybrid systems or specialized fleets. The success of future cleaning missions—such as the upcoming ClearSpace-1 and the operational follow-ups to ADRAS-J—will depend less on conceptual novelty and more on robust mechanical design: the ability of a mechanism to absorb shock, tolerate uncertainty, and maintain structural integrity under worst-case dynamic loads. As the orbital environment grows more congested, the mechanical engineering community must prioritize these \"nuts and bolts\" realities of contact dynamics to ensure the sustainable use of space.

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Copyright

Copyright © 2026 Ketan Totlani. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.