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Space tethers are long cables which can be used for propulsion, momentum exchange, stabilization and altitude control, or maintaining the relative positions of the components of a large dispersed satellite/spacecraft sensor system.〔NASA, (Tethers In Space Handbook ), edited by M. L. Cosmo and E. C. Lorenzini, third edition December 1997 (accessed 20 October 2010); see also version of (NASA MSFC ); available on (scribd ''www.scribd.com'' )〕 Depending on the mission objectives and altitude, spaceflight using this form of spacecraft propulsion may be significantly less expensive than spaceflight using rocket engines. ==Main techniques== Four main techniques for employing space tethers are in development: Electrodynamic tethers :Electrodynamic tethers are primarily used for propulsion. These are conducting tethers that carry a current that can generate either thrust or drag from a planetary magnetic field, in much the same way as an electric motor does. Momentum exchange tethers :These can be either rotating tethers, or non-rotating tethers, that capture an arriving spacecraft and then release it at a later time into a different orbit with a different velocity. Momentum exchange tethers can be used for orbital maneuvering, or as part of a planetary-surface-to-orbit / orbit-to-escape-velocity space transportation system. Tethered formation flying :This is typically a non-conductive tether that accurately maintains a set distance between multiple space vehicles flying in formation. Electric sail :A form of solar wind sail with electrically charged tethers that will be pushed by the momentum of solar wind ions. Many uses for space tethers have been proposed, including deployment as space elevators, as skyhooks, and for doing propellant-free orbital transfers. 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「Space tether」の詳細全文を読む スポンサード リンク
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