Electrodynamic tethers for reboost of the International Space Station and spacecraft propulsion

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The International Space Station (ISS) will require periodic reboost due to atmospheric aerodynamic drag. This is nominally achieved through the use of thruster firings by the attached Progress M spacecraft. Many Progress flights to the ISS are required annually. Electrodynamic tethers provide an attractive alternative in that they can provide periodic reboost or continuous drag cancellation using no consumables, propellant, nor conventional propulsion elements. The system could also serve as an emergency backup reboost system used only in the event resupply and reboost are delayed for some reason. The system also has direct application to spacecraft and upper stage propulsion. Electrodynamic tethers have been demonstrated in space previously with the Plasma Motor Generator (PMG) experiment and the Tethered Satellite System (TSS-1R). The advanced electrodynamic tether proposed for this application has significant advantages over previous systems in that higher thrust is achievable with significantly shorter tethers and without the need for an active current collection device, hence making the system simpler and much less expensive. Propellantless Reboost for the ISS: An Electrodvnamic Tether Thruster The need for an alternative to chemical thruster reboost of the ISS has become increasingly apparent as the station nears completion. We propose a system to utilize ISS electrical power to generate thrust by means of a new type of electrodynamic tether attached to the station (Fig. 1). A flexible system could be developed to generate an average thrust of 0.5 to 0.8 N for 5 to 10 kW of electrical power. By comparison, aerodynamic drag on 755 is expected to average from 0.3 to 1.1 N (depending upon the year). The proposed system uses a tether with a kilometers-long uninsulated (bare) segment capable of collecting currents greater than 10 A from the ionosphere. The new design exhibits a remarkable insensitivity to electron density variations, allowing it