Optimal Control of Retrieval of a Tethered Subsatellite

Abstract

AbstractThe most important and complicated operations during a tethered satellite system mission are deployment and retrieval of a subsatellite from or to a space ship. The deployment process has been treated in [15]. In this paper retrieval is considered. We restrict to the practically important case that the system is moving on a circular Keplerian orbit around the Earth. The main problem during retrieval is that it results in an unstable motion concerning the radial relative equilibrium which is stable for a tether of constant length. The uncontrolled retrieval results in a strong oscillatory motion. Hence for the practically useful retrieval of a subsatellite this process must be controlled. We propose an optimal control strategy using the Maximum Principle to achieve a force controlled retrieval of the tethered subsatellite from the radial relative equilibrium position far away from the space ship to the radial relative equilibrium position close to the space ship.Key wordsTime optimal controlmaximum principlePontrijaginspace pendulum