Electrodynamic tethers for deorbiting applications

In this paper the de-orbiting performance of various tether configurations have been studied and compared with each other. Three different configurations have been analyzed. An insulated conducting tether terminated with a balloon at the upper end (ITB), a bare tether only (BTO) and a bare tether terminated with a balloon (BTB). The drag forces obtained with the various systems have been computed taking into account the tether equivalent electric circuit which includes, besides the ohmic resistance of the wire, the effects of the plasma sheaths resulting from the interaction with the ionospheric plasma. The orbit decay times for a spacecraft of 500 kg mass equipped with a 5 km long tether, in the three different configurations, have been computed by using a simple model of the average ionospheric density profile. The BTB configuration turns out to be the one which exhibits the best de-orbiting performance. The total de-orbiting time from an altitude of 1300 km down to 200 km is 23 days for a system BTB, 32 days for ITB and 66 days for BTO.