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Dynamical, Electrical, and Thermal Coupling in a New Class of Electrodynamic Tethered Satellites
No full textOverview of Future NASA Tether Applications
Full text linkThe groundwork has been laid for tether applications in space. NASA has developed tether technology for space applications since the 1960's. Important recent milestones include retrieval of a tether in space (TSS-1, 1992), successful deployment of a 20-km-long tether in space (SEDS-1, 1993), and operation of an electrodynamic tether with tether current driven in both directions-power and thrust modes (PMG, 1993). Various types of tethers and systems can be used for space transportation. Short electrodynamic tethers can use solar power to 'push' against a planetary magnetic field to achieve propulsion without the expenditure of propellant. The planned Propulsive Small Expendable Deployer System (ProSEDS) experiment will demonstrate electrodynamic tether thrust during its flight in early 2000. Utilizing completely different physical principles, long non-conducting tethers can exchange momentum between two masses in orbit to place one body into a higher orbit or a transfer orbit for lunar and planetary missions. Recently completed system studies of this concept indicate that it would be a relatively low-cost in-space asset with long-term multi-mission capability. Tethers can also be used to support space science by providing a mechanism for precision formation flying and for reaching regions of the upper atmosphere that were previously inaccessible
Efficiency of Electrodynamic Tether Thrusters
No full textAbstract. The performance efficiency of electrodynamic bare tethers acting as thrusters in low Earth orbit, as gauged by
the ratio of the system mass dedicated to thrust over mission impulse, is analyzed and compared to the performance
efficiency of electrical thrusters. Tether systems are much lighter for times beyond six months in space-tug
operations, where there is a dedicated solar array, and beyond one month for reboost of the International Space
Station, where the solar array is already in place. Bare-tether propulsive efficiency itself, with the tether considered
as part of the power plant, is higher for space tugs. Tether optimization shows that thin tapes have greater propulsive
efficiency and are less sensitive to plasma density variations in orbit than cylindrical tethers. The efficiency
increases with tape length if some segment next to the power supply at the top is insulated to make the tether
potential bias vanish at the lower end; multitape tethers must be used to keep the efficiency high at high thrust
levels. The efficiency has a maximum for tether-hardware mass equal to the fraction of power-subsystem mass
going into ohmic power, though the maximum is very flat. For space tugs, effects of induced-bias changes in orbit
might need to be reduced by choosing a moderately large power-subsystem to tether-hardware mass ratio or by
tracking the current-voltage characteristic of the solar array
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