Tethered Satellite controlled re-entry dynamics from the International Space Station

Payloads left in space at the end of life create debris. A high number of space debris surround our planet and within a few years, experts argue, it will no longer be possible to send payloads safely into space. Our studies strive to demonstrate the ability to bring a payload back to Earth without the use of active propulsion system in close proximity of the ISS. The use of a classical chemical propulsion system near sensitive and inhabited space areas can generate risks and cause 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 an onboard a re-entry capsule, employed to execute the first part of the release/deployment maneuver. The tether deployment trajectory must be controlled in order to provide a high 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 pre-determine reference trajectory. Relevant details of the IR sensors (photocells) that are planned for the measuring the input parameters are also presented. The aim of our study is to propose a safe and pollution-free solution for deorbiting a controlled space vehicle from the ISS, preventing hazards and minimizing external contamination.