Deorbiting of spacecraft at the end of life with electrodynamic tethers stabilized by passive oscillation dampers

Abstract - Since the beginning of human space era the number of debris orbiting the Earth produced accidentally or intentionally by artificial satellites has been continuously growing. Nevertheless, only in the last years the alarming growth of space debris induced 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. Our task, which is part of an international EU-funded project, is to develop a new technology suitable to deorbit a satellite at the end of life with as small an impact as possible on the mass budget of the mission. In fact, a deorbit maneuver with chemical rockets can strongly affect the satellite propulsion budget, thus limiting the operational life of the satellite. An alternative to the traditional chemical rockets consists in using an electrodynamic tether that, through its interaction with the Earth ionosphere and magnetic field, can take advantage of Lorentz forces for deorbiting purposes. This is a particularly promising technique because it is passive, light and effective. However, Lorentz forces produce a low and yet continuous injection of energy into the system that, in the long run, can bring the tether to instability. This paper addresses this issue through the analysis of the benefits provided by a viscous damping device installed at the attachment point of the tether to the spacecraft. The analysis carried out by means of linearization of dynamics equations and numerical simulations show that a well-tuned damper can efficiently absorb the kinetic energy from the tether thus greatly increasing the system stability.