Performance of bare-tether systems under varying magnetic and plasma conditions

Electrodynamic tethered systems, in which an exposed portion of the conduct ing tether itself collects electrons from the ionosphere, promise to attain currents of 10 A or more in low Earth orbit. For the first time, another d esirable feature of such bare-tether systems is reported and analyzed in de tail: Collection by a bare tether is relatively insensitive to variations i n electron density that are regularly encountered on each revolution of an orbit. This self-adjusting property of bare-tether systems occurs because t he electron-collecting area on the tether is not fixed, but extends along i ts positively biased portion, and because the current varies as collecting length to a power greater than unity, How this adjustment to density variat ions follows from the basic collection law of thin cylinders is shown. The effect of variations in the motionally induced tether voltage is also analy zed. Both power and thruster modes are considered. The performance of bare tether systems to tethered systems is compared using passive spherical coll ectors of fixed area, taking into consideration recent experimental results . Calculations taking into account motional voltage and plasma density arou nd a realistic orbit for bare-tether systems suitable for space station app lications are also presented.