Analysis of Passive System to Damp the Libration of Electrodynamic Tethers for Deorbiting

Abstract

In the last decade, the continuous and alarming growth of space debris prompted many space agencies all over the world to adopt debris mitigation strategies. Present guidelines indicate the need to deorbit new satellites launched into low Earth orbit (LEO) within 25 years from their end of life. At present, a space-proven technology suitable to carry out a complete deorbit utilizes classical chemical propulsion. However, a deorbit maneuver by means of chemical rocket strongly affects the satellite propulsion budget, thus limiting the operational life of the satellite. These issues bring the need to develop innovative deorbiting technologies. One of these consists in using electrodynamic tethers that, through its interaction with the Earth ionosphere and magnetic field, can take advantage of Lorentz forces for deorbiting. Previous studies have shown the effectiveness of such a technology to deorbit LEO satellites from different altitudes and inclinations in a relatively short time. However, the continuous injection of small amount of energy produced by Lorentz forces into the tether system can cause dynamic instabilities. This paper addresses this issue through the analysis of the benefits provided by a damping device installed at the attachment point of the tether to the spacecraft. The damped tether system is modeled with a two-bar model to represent the dynamics of the tether and damping device. A key issue is how to maximize the energy transfer from the electrodynamic tether to the damper and its dissipation. The analysis carried out by means of linearization of dynamics equations and numerical simulations show that a well-tuned damper can effciently damp out the tether kinetic energy thus greatly increasing the system stability.