Tethered Satellite-Controlled Re-Entry Dynamics From the International Space Station

Payloads left in space at the end of life create debris. A large amount of space debris surrounds our planet and within a few years, experts argue, it will no longer be possible to send payloads safely into space. Our study strives to demonstrate the ability to bring a payload back to Earth without the use of an active propulsion system in close proximity of the International Space Station (ISS). The use of a classical chemical propulsion system near sensitive and inhabited space areas is risky and causes contamination due to the fuel ejection. Consequently, the design of a passive but controlled vehicle, that satisfies safety and free-pollution requirements, needs a new propulsive technology. A possible solution is using a Tether Subsystem, mounted onboard a re-entry capsule, employed to execute the first phase of the release/deployment maneuver. The tether deployment trajectory must be controlled in order to provide a large libration angle of about 40° and a radial velocity near zero at the end of tether deployment. The control algorithm adopted is based on reliable and easy to measure dynamics parameters: the deployed length and length rate are the inputs of the control loop that forces the tethered capsule to follow a predetermine reference trajectory during deployment. Relevant details of the IR sensors (i.e., photocells) that are planned for measuring the input parameters are also presented. The aim of our study is to propose a safe and pollution-free solution for separating small satellites from the ISS, preventing hazards, and minimizing external contamination.