OBSERVATIONS OF IONOSPHERE HEATING IN THE TSS-1 SUBSATELLITE PRESHEATH

The first flight of the Tethered Satellite System (TSS- 1) was to inve stigate the mechanical and electrical dynamics of a conducting satelli te 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 orb iter radially away from the Earth. The relative motion between the tet her and Earth's magnetic field generated an electromotive force (EMF) that is the product of orbiter velocity, Earth's magnetic field, and t he length of the deployed tether. This EMF drove a current through the tether. Electrons were collected on the satellite's electrically cond uctive skin and traveled through the tether to the orbiter, where they either went to orbiter structural ground or were emitted into the ion osphere via active electron emission. During TSS-1 this electron emiss ion was accomplished mainly by the 100 mA, 1-keV fast pulsed electron gun (FPEG) of the shuttle electrodynamic tether system (SETS) (William son 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 collecti on at the satellite. Potentials of the orbiter with respect to the amb ient plasma were obtained from measurements from the Shuttle Potential and Return Electron Experiment (SPREE) (Oberhardt et al., 1993a, b, 1 994), the SETS tether current voltage monitor (Thompson et al., 1993), and the Agenzia Spaziale Italiana deployer and satellite core equipme nt (Bonifazi et al., 1988, 1994). Despite the limited tether deploymen t length of 268 m the TSS-1 system proved capable, during certain even ts. of generating satellite potentials sufficient to illuminate a prev iously unexplored aspect of plasma physics: that of an ion repelling, electron attracting, moving probe in a magnetoplasma. During such even ts the satellite boom-mounted Langmuir probe flown as part of the Rese arch on Electrodynamic Tethers experiment (Dobrowolny et al., 1994) me asured an increase in the electron plasma temperature in the quasi-neu tral ionospheric region beyond the satellite sheath. This observed hea ting of the presheath electrons was distinctly different from the acce leration 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 consisten t with the formation of a Bohm stable electron collecting sheath.