Performance of Bare-Tether Systems Under Varying Magnetic and Plasma Conditions

Electrodynamic tethered systems, in which an exposed portion of the conducting tether itself collects electrons from the ionosphere, promise to attain currents of 10 A or more in low Earth orbit. For the e rst time, another desirable feature of such bare-tether systems is reported and analyzed in detail: Collection by a bare tether is relatively insensitive tovariations inelectron densitythat are regularly encountered on each revolution of an orbit. This self-adjusting property of bare-tether systems occurs because the electron-collecting area on the tether is not exed, but extends along its positively biased portion, and because the current varies as collecting length to a power greater than unity. How this adjustment to density variations follows from the basic collection law of thin cylinders is shown. The effect of variations in the motionally induced tether voltage is also analyzed. Both power and thruster modes are considered. The performance ofbare-tether systems totethered systems is compared using passive spherical collectors of exedarea, takingintoconsideration recent experimental results. Calculations taking intoaccount motionalvoltage and plasmadensityaround arealistic orbit for bare-tether systems suitablefor space station applications are also presented.