Abstract:
Electrodynamic tethers are long conducting wires which is used to power satellite , the one deployed from the tether satellite, The gravity gradient field (also known as the "tidal force") will tend to orient the tether in a vertical position. If the tether is orbiting around the Earth, it will be crossing the Earth's magnetic field lines at orbital velocity (7-8 km/s!). The motion of the conductor across the magnetic field induces a voltage along the length of the tether. This voltage can be up to several hundred volts per kilometer.which is based on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, An EDT takes advantage of two basic principles of electromagnetism: current is produced when a conductive wire moves through a magnetic field, and the field exerts a force on the current, or as motors, converting electrical energy to kinetic energy. Electric potential is generated across a conductive tether by its motion through the Earth's magnetic field. The choice of the metal conductor to be used in an electrodynamic tether is determined by a variety of factors. Such as high electrical conductivity, and low density. Secondary factors, depending on the application, include cost, strength, and melting point. An EDT system is made up of two masses in orbit connected by a long, flexible, electrically conductive cable; the tether is essentially a wire that moves through the magnetic field of the Earth (or another planet or large body)
please read
http://highfrontierArchive/Jt/Tethers%20Scient%20Amer%200804050.pdf
http://en.wikipediawiki/Electrodynamic_tether
http://spacebusinesstechnology/technology/technovel_tether_041109.html