Investigation of the current collected by a positively biased satellite with application to electrodynamic tethers

Abstract

The interaction between a positively biased body traveling through an ionospheric space plasma has direct application to electrodynamic tether (EDT) systems. A 2‐D3v particle‐in‐cell model has been developed to study the plasma dynamics near a positively charged EDT system end‐body and their impact on the current collected. The results show that the azimuthal current structures observed during the reflight of the tethered satellite system (TSS‐1R) mission develop in the simulations and are found to enhance the current collected by the satellite by 67% when the magnetic field is ∼15° off of perpendicular to the orbital velocity. As the component of the magnetic field in the simulation's plane increases, the electrons are not able to easily cross the field lines causing plasma lobes to form in the +y and −y regions around the satellite. The lobes limit the current arriving at the satellite and also cause an enhanced wake to develop. A high satellite bias causes a stable bow shock structure to form in the ram region of the satellite, which limits the number of electrons entering the sheath region and thus limits the current collected. Electron‐neutral collisions are found to destabilize the bow shock structure, and its current limiting effects were negated. Analytical curve fits based on the simulations are presented in order to characterize the dependence of the current collected on the magnetic field's orientation, space plasma magnetization, and satellite potential. The variations in the collected current induced by space plasma environmental changes may introduce new instabilities in an EDT system's dynamics.

A parallel particle-in-cell code for spacecraft charging problems

“…For drifting plasma flows, usually the measured or simulated currents can be several times larger than the theoretically predicted values. One example is the magnetic limited electron currents collected by the tethering cable during the TSS-1R experiment in space (Janeski, Scales & Hall 2014;Cooke & Katz 1998;Cai 2017). In figure 23(c), the Y-axis represents the simulation results, and the X-axis represents the theoretical values predicted by the Parker-Murphy theory.…”

Kinetic analysis of the plasma sheath around an electron-emitting object with elliptic cross section

“…Sheath structures arising from the self-organisation of a plasma surrounding an object are ubiquitous in plasma physics [1]. Langmuir Probes (LPs) and Emissive Probes (EPs) [2][3][4][5][6][7][8], charging of grains in complex plasmas [9][10][11][12], spacecraft charging [13][14][15][16], and current collection/emission by Electrodynamic Tethers (EDTs) [17][18][19][20] are some interesting examples. Kinetic descriptions, involving complex analytical analysis and significant computational resources in numerical simulations, are typically required to correctly capture essential features of the sheaths.…”