NASA is hoping to use electrodynamic space tethers (EDT) to adjust the orbit altitudes of spacecraft, with a trial planned for next year.
The propulsive small expendable deployer system (ProSEDS) experiment will be launched from an expendable rocket, and will deploy an ultra-thin 15km (9.3m)-long tether, part of which will be a bare-wire conductor (Flight International, 19-26 February 2002). The experiment is designed to use EDT technology to drag the Delta rocket stage from which it is deployed back into the Earth's atmosphere to burn up.
Space tethers have long been proposed as methods of changing the orbital height of satellites by exchanging momentum between two masses, such as two satellites at different orbital heights. In the past, conducting tethers have also been flown which can generate electrical current as they pass through the Earth's magnetic field.
The ProSEDS experiment is different in that it relies on momentum exchange resulting from the flow of current through the tether. Converting some of the satellite's kinetic energy into electrical power causes the satellite to slow down gradually, decaying its orbit to the point where it re-enters the Earth's atmosphere. NASA says such a system could be used to remove "space junk", such as a satellite at the end of its useful life.
NASA believes the principle could work equally well in reverse. By forcing a current through the tether in the other direction, energy is added to the orbit of the tether which boosts it - and the attached satellite - into a higher orbit. The current could be drawn from solar panels on the satellite.
NASA says such a tether could be used to continually reboost the orbit of the International Space Station, countering the effect of atmospheric drag without requiring additional propellant.
Source: Flight International
