Space Studies Institute Report on Space Shuttle External Tank Applications by J. Alex Gimarc 12-01-1985 copyright Space Studies Institute The use of momentum transfer by the space station, orbiter, or the orbiter/ET combination would result in overall savings in onboard fuels, possible opening up of higher orbits to the orbiter, and insertion of the ET into a high orbit without expenditure of any residual cryogenics. If the ET and orbiter are tethered together, spun up to an appropriate rate, and released at the correct time and attitude, the ET orbit could be raised 40 x 560 km and the orbiter could have its orbit lowered 10 x 130 km, or low enough to deorbit. Loads on a tether in this case are less than 4,000 lbs tension. This is well within existing tether material capabilities today (50, 56). C. Electromagnetic Effects The final possible application discussed here involves the use of a tether as an electrical device. In addition to moving through space, bodies in LEO are also moving through a plasma in a magnetic field. As a result of these effects, there is a net potential difference between the bodies on either end on the order of 200 volts/km. If the tether is made of a conducting material and properly connected, a substantial current could be drawn for onboard power. A proposed design for power has been made that will deliver between 5-65 kilowatts continuously (13, 56, 84). As with any other application, there is a tradeoff with this form of electrical power generation. It induces additional drag on the station by interaction with the magnetic field during power generation. This means that the momentum of a tethered station becomes an electrical energy storage device. As electrical power is generated, the station’s orbit decays. Any method of supplying additional mass to be released below the station thereby becomes a method of supplying future electrical requirements. Calculations of a station that will lower and then release a visiting orbiter 150 km below the station will generate over 9,000 kilowatt hours (kwh) of electricity without orbital decay (56). There is a reverse application to this power generation scheme. The Alfven Engine has been proposed by Drell et al. as a method of orbit maintenance, plane changing, orbit raising, manuvering, and excess energy conversion (13, 56, 84). If excess electrical power exists, a current flow could be forced against the potential work against the magnetic field. Theoretical efficiencies of 50X have been suggested. If this proves feasable.
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