Thrust-Aided Librating Deployment of Tape Tethers

Abstract

This paper addresses issues relevant to the deployment operations of a multikilometer tape-shaped tether from an orbiting spacecraft with the aid of an inline low-thrust propulsion system located inside the tip mass to be deployed. The study is part of a technology development project of an end-of-life deorbiting device for debris mitigation that uses an electrodynamic tether to produce a drag force according to the Lorenz law. The tether must be deployed from a nontumbling satellite with a swinging maneuver that follows a predetermined trajectory. A suitable set of reference trajectories was found by means of a numerical nonlinear optimization using the Nelder–Mead algorithm for tethers of different lengths. Each reference trajectory is fed forward to a proportional-derivative closed-loop brake control system integrated in the tether deployer. A sensitivity analysis was carried out to pinpoint the reference trajectories that minimize the residual libration at the end of the deployment, thus providing the highest level of dynamical stability to the tethered system. The tip mass attitude stability was also investigated to determine a geometrical configuration of the propulsion subsystem suitable for stability.