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An electrically powered spacecraft propulsion system uses electrical energy to change the velocity of a spacecraft. Most of these kinds of spacecraft propulsion systems work by electrically expelling propellant (reaction mass) at high speed, but electrodynamic tethers work by interacting with a planet's magnetic field.〔Michel Van Pelt ''Space Tethers and Space Elevators'' Springer, 2009 ISBN 0387765565, page 24〕 Electric thrusters typically use much less propellant than chemical rockets because they have a higher exhaust speed (operate at a higher specific impulse) than chemical rockets.〔Choueiri, Edgar Y. (2009) (New dawn of electric rocket ) ''Scientific American'' 300, 58–65 〕 Due to limited electric power the thrust is much weaker compared to chemical rockets, but electric propulsion can provide a small thrust for a long time. Electric propulsion can achieve high speeds over long periods and thus can work better than chemical rockets for some deep space missions.〔 Electric propulsion is now a mature and widely used technology on spacecraft. Russian satellites have used electric propulsion for decades.〔http://fluid.ippt.gov.pl/sbarral/hall.html〕 As of 2013, over 200 spacecraft operated throughout the solar system use electric propulsion for stationkeeping, orbit raising, or primary propulsion.〔W. Andrew Hoskins et al. "30 Years of Electric Propulsion Flight Experience at Aerojet Rocketdyne", Paper IEPC-2013-439, 33rd International Electric Propulsion Conference, Washington DC, October 2013. http://www.iepc2013.org/get?id=439〕 In the future, the most advanced electric thrusters may be able to impart a Delta-v of 100 km/s, which is enough to take a spacecraft to the outer planets of the Solar System (with nuclear power), but is insufficient for interstellar travel.〔〔(Choueiri, Edgar Y. (2009). New dawn of electric rocket )〕 Also, an electro-rocket with an external power source (transmissible through laser on the solar panels) has a theoretical possibility for interstellar flight.〔(Laser-Powered Interstellar Probe G Landis - APS Bulletin, 1991 )〕〔(Geoffrey A. Landis. Laser-powered Interstellar Probe ) on the (Geoffrey A. Landis: Science. papers available on the web )〕 However, electric propulsion is not a method suitable for launches from the Earth's surface, as on average the thrust for such systems is too weak. ==History== The idea of electric propulsion for spacecraft dates back to 1911, introduced in a publication by Konstantin Tsiolkovsky. Earlier, Robert Goddard had noted such a possibility in his personal notebook. Electrically powered propulsion with a nuclear reactor was considered by Dr. Tony Martin for interstellar Project Daedalus in 1973, but the novel approach was rejected because of very low thrust, much weight needed to convert nuclear energy into electrical equipment and as a result a small acceleration, which would take a century to achieve the desired speed.〔(PROJECT DAEDALUS: THE PROPULSION SYSTEM Part 1; Theoretical considerations and calculations. 2. REVIEW OF ADVANCED PROPULSION SYSTEMS )〕 The first in-space demonstration of electric propulsion was an ion engine carried on board the SERT-1 (Space Electric Rocket Test) spacecraft,〔(NASA Glenn Contributions to Deep Space 1 )〕〔Ronald J. Cybulski, Daniel M. Shellhammer, Robert R. LoveII, Edward J. Domino, and Joseph T. Kotnik, (RESULTS FROM SERT I ION ROCKET FLIGHT TEST ), NASA Technical Note D2718 (1965).〕 launched on 20 July 1964 and it operated for 31 minutes.〔 A follow-up mission launched on 3 February 1970, SERT-2, carried two ion thrusters, one operated for more than five months and the other for almost three months.〔〔NASA Glenn, ("SPACE ELECTRIC ROCKET TEST II (SERT II)" ) (Accessed 1 July 2010)〕〔(SERT ) page at Astronautix (Accessed 1 July 2010)〕 By the early 2010s, many satellite manufacturers were offering electric propulsion options on their satellites—mostly for on-orbit attitude control—while some commercial communication satellite operators were beginning to use them for geosynchronous orbit insertion in place of traditional chemical rocket engines.〔 〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Electrically powered spacecraft propulsion」の詳細全文を読む スポンサード リンク
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