Drag Compensation for Space Stations

 

For a spacecraft in a very Low Earth Orbit (LEO), the atmospheric drag is sufficiently strong to cause a re-entry before the intended end of the mission. Orbit raising maneuvers must be executed on a regular basis. A typical example of this is the International Space Station (ISS) which has an operational altitude of 200-250 miles above Earth surface. Due to atmospheric drag, the space station is constantly losing orbital energy. In order to compensate for this loss, which would eventually lead to a re-entry of the station, it is from time to time being “re-boosted” to a higher orbit. The chosen orbital altitude is a trade-off between time required between re-boost maneuvers and the increased cost of delivering payloads and people to a higher altitude. The upper limitation of orbital altitude is imposed by the capability of the Soyuz spacecraft. Annually, NASA and the Russian Space Agency spend between 5 and 12 t of propellant in order to keep the station on the intended orbit, using chemical boosters ( L. Johnson, M. Herrmann “ISS Electrodynamic Tether Reboost Study”, NASA/TM-1998-208538). SEP-VASIMR® system would reduce the propellant use for ISS or future private space stations drag compensation, because of using higher specific impulse propulsion, by 15 times.