Magnetic self‐field effects on current collection by an ionospheric bare tether

Abstract

[1] It was recently suggested that the magnetic field created by the current of a bare tether strongly reduces its own electron-collection capability when a magnetic separatrix disconnecting ambient magnetized plasma from tether extends beyond its electric sheath. It is here shown that current reduction by the self-field depends on the ratio L * /L t parameterizing bias and current profiles along the tether (L t tether length, L * characteristic length gauging ohmic effects) and on a new dimensionless number K s involving ambient and tether parameters. Current reduction is weaker the lower K s and L * / L t , which depend critically on the type of cross section: K s varies as R 5/3, h 2/3 R, and h 2/3 Â 1/4 width for wires, round tethers conductive only in a thin layer, and thin tapes, respectively; L * varies as R 2/3 for wires and as h 2/3 for tapes and round tethers conductive in a layer (R radius, h thickness). Self-field effects are fully negligible for the last two types of cross sections whatever the mode of operation. In practical efficient tether systems having L * /L t low, maximum current reduction in case of wires is again negligible for power generation; for deorbiting, reduction is <1% for a 10 km tether and $15% for a 20 km tether. In the reboost mode there are no effects for K s below some threshold; moderate effects may occur in practical but heavy reboost-wire systems that need no dedicated solar power.INDEX TERMS: 7807 Space Plasma Physics: Charged particle motion and acceleration; 7815 Space Plasma Physics: Electrostatic structures; 7853 Space Plasma Physics: Spacecraft/atmosphere interactions; 7855 Space Plasma Physics: Spacecraft sheaths, wakes, charging; KEYWORDS: ionospheric tethers, bare tethers, magnetic self-field of tethers, magnetic effects on current collection, orbital-motionlimited current, magnetic topology Citation: Sanmartin, J. R., and R. D. Estes, Magnetic self-field effects on current collection by an ionospheric bare tether,

Analyses of Bare-Tether Systems as a Thruster for MXER Studies

“…In more details this is discussed by Khazanov et al [2000Khazanov et al [ , 2001. Sanmartin and Estes [2002] proposed a similar model of magnetic shielding as Khazanov et al [2000Khazanov et al [ , 2001 with two changes. They neglect the current due to thermal motion of particles across the separatrix by assuming that the collected current is zero, if the separatrix is inside the plasma sheath.…”

“…Results of this study are based on the model of magnetic shielding of Khazanov et al [2000Khazanov et al [ , 2001. Below we present the comparison of this model with the model of magnetic shielding developed by Sanmartin and Estes [2002].…”

“…The detailed formulation of the problem is presented by Sanmartin et al [1993], Khazanov et al [2000Khazanov et al [ , 2001, and Sanmartin and Estes [2002].…”

“…Different parameters describing tether performance, such as system acceleration and efficiency can be calculated, if the current distribution along the tether at the satellite trajectory is known. Below we present the results of current calculation along the expected trajectory of the MXER tether for wire and tape tethers with different cross-sections, and discuss the magnetic shielding effects based on the results of Khazanov et al [2001], Sanmartin and Estes [2002] papers, and the results of these calculations.…”

Energy Analysis of Bare Electrodynamic Tethers

“…They represent a simple and robust solution to current collection in highly rarefied plasmas. Subsequent papers have explored their operational regime [orbit motion limit (OML)] [10], validity range [16], and other relevant issues [17,18].…”