Dynamics of Tethered Space-Robot Swarm for Active Debris Removal

Recent space activity trends herald a huge increase in the frequency of space launches and plans for constellations of satellites in space in the very near future. This calls for active measures to remove space debris from the orbits to maintain sustainable space access. This is mainly due to the high risk of collision of active spacecrafts with space debris that can easily lead to the failure of missions. Methods like space tether and tethered net are active areas of research and stand as promising candidates for low-cost and effective solutions to mitigate space debris. However, the success rate of capturing debris in conventional methods is debatable. This paper discusses the application of a swarm of agents attached to a space debris using space teth-ers to perform cooperative orbital maneuver of the space debris. The application of a swarm instead of a monolithic space robot boosts the flexibility, reusability, and robustness of the missions and improves the success rate of capturing the space debris of different shapes and sizes. A swarm of CubeSats attached to a rigid body space debris via space tethers is modeled. The space tether is modeled as a series of lumped masses to account for its dynamics and flexibility. The dynamics of the coupled nonlinear system are studied and swarm control laws are formulated using Artificial Potential Field method. The proposal of decentralized control of the swarm opens the possibility of scaling the missions to cooperatively work in numbers which can be computationally too expensive otherwise. A deorbiting control for the swarm is proposed such that it maximizes the decay rate of the semimajor axis. Numerical simulation results show that the proposed swarm control is capable of detumbling the space debris and deorbit it into the atmosphere from Lower Earth Orbit (LEO).