NEGATIVE PICKUP IONS DETECTED DURING THE TSS-1 MISSION

We report the occasional detection of negative pickup ions by the Shut tle Potential and Return Electron Experiment (SPREE) in the shuttle pa yload bay during the first Tethered Satellite System (TSS 1) mission. These ions appear as arch-like structures of enhanced fluxes in energy versus time spectrograms for the SPREE electron zone looking in the p lane perpendicular to the Earth's magnetic field. Maximum energies of similar to 56 eV were measured when the sensor looked closest to the s huttle ram direction, Empirically, the energy of associated spectral p eaks decreases as cos(2) xi, where xi is the angle between the sensor look direction and the projection of the shuttle's velocity onto the p lane perpendicular to the magnetic field. These signatures may be foun d under day or night conditions and always in conjunction with positiv ely charged pickup ions generated as a result of firings by the L5D an d/or R5D vernier thrusters. We show that positive ion contamination an d accelerated electrons cannot be the responsible agents. Observed spe ctral characteristics are most easily explained as either NO2- or MMH( -) ions created near the shuttle and accelerated by the motional elect ric field to energies detectable by SPREE.