Observations of ionosphere heating in the TSS‐1 subsatellite presheath

Abstract

The first flight of the Tethered Satellite System (TSS‐1) was to investigate the mechanical and electrical dynamics of a conducting satellite deployed from the orbiter via a tether whose core was a conducting wire [Dobrowolny and Melchioni, 1993; Dobrowolny, 1987; Dobrowolny and Stone, 1994). In the TSS‐1 system the satellite deployed from the orbiter radially away from the Earth. The relative motion between the tether and Earth's magnetic field generated an electromotive force (EMF) that is the product of orbiter velocity, Earth's magnetic field, and the length of the deployed tether. This EMF drove a current through the tether. Electrons were collected on the satellite's electrically conductive skin and traveled through the tether to the orbiter, where they either went to orbiter structural ground or were emitted into the ionosphere via active electron emission. During TSS‐1 this electron emission was accomplished mainly by the 100 mA, 1‐keV fast pulsed electron gun (FPEG) of the shuttle electrodynamic tether system (SETS) (Williamson et al., 1988; Banks et al., 1994; V. M. Aguero et al., manuscript in preparation, 1994]. The FPEG electron emission was much higher than either ambient ion collection at the orbiter end or electron collection at the satellite. Potentials of the orbiter with respect to the ambient plasma were obtained from measurements from the Shuttle Potential and Return Electron Experiment (SPREE) (Oberhardt et al., 1993a, b, 1994), the SETS tether current voltage monitor (Thompson et al., 1993), and the Agenzia Spaziale Italiana deployer and satellite core equipment (Bonifazi et al., 1988, 1994). Despite the limited tether deployment length of 268 m the TSS‐1 system proved capable, during certain events, of generating satellite potentials sufficient to illuminate a previously unexplored aspect of plasma physics: that of an ion repelling, electron attracting, moving probe in a magnetoplasma. During such events the satellite boom‐mounted Langmuir probe flown as part of the Research on Electrodynamic Tethers experiment (Dobrowolny et al., 1994) measured an increase in the electron plasma temperature in the quasi‐neutral ionospheric region beyond the satellite sheath. This observed heating of the presheath electrons was distinctly different from the acceleration of the electrons in the sheath, which was also observed when the sheath expanded such that the probe was completely in the sheath. We show that the observed elevated electron temperatures are consistent with the formation of a Bohm stable electron collecting sheath.

TSS‐1R electron currents: Magnetic limited collection from a heated presheath

“…The predictions of our model are in remarkable agreement with the published TSS-1R data. As was true when the original paper [Katz et al, 1994] was published, the detailed mechanism that generates the scattering and the scattering frequency is still not understood.…”

Analysis of chamber simulations of long collecting probes in high-speed dense plasmas

“…It is interesting to note that a change in current collection behavior beyond a certain bias threshold was also seen in the TSS-1R [24] and TSS-1 missions [25] where the threshold was at a potential of the ionospheric ion ram kinetic energy. Specifically, the TSS-1R results found that as the satellite potential exceeded the ram kinetic energy of O ions (5.3 eV), the level of kilohertz wave activity increased dramatically [26] and a suprathermal electron population appeared at the satellite's surface [27].…”

Current collection by a positively charged spacecraft: Effects of its magnetic presheath

“…The latter value is very different from ours, but this difference is not surprising in view of the dissimilarities between their assumptions and ours. Katz et al [1994Katz et al [ , 1995 also note that at the angular location of the RETE Langmuir probe on TSS-1, their calculation yields an electron temperature ranging from about 0.5 eV down to ambient as radius increases, and…”