BEAM ARC DISTRIBUTIONS OF SHUTTLE PICKUP IONS AND THEIR INSTABILITIES

Data from the Shuttle Potential and Return Electron Experiment (SPREE) flown as part of the Tethered Satellite System (TSS 1) are used to de termine the detailed characteristics of beam are distributions of pick up ions due to molecules outgassed or ejected from the shuttle. These ion distributions are only detected near the plane perpendicular to th e magnetic field direction in an angular range of +/-45 degrees about the minimum angle to ram. Their flux is largest when the angle between this plane and the shuttle ram direction is smallest. Generally, ion spectra peak in the range 19 to 25 eV at the minimum angle between the perpendicular plane and the ram direction. The peak energy decreases smoothly as this angle increases. Weak fluxes are measured above the p eak, to energies as high as 150 eV. Within the SPREE energy range, two -dimensional distribution functions of beam are ions in the perpendicu lar plane have teardrop shapes, symmetric about the minimum angle to s huttle ram with deep minima in the centers. Variations in the peak ene rgies of differential number fluxes agree with collisionless trajector y analysis, assuming that the ions are H2O+ and allowing for different initial velocities before charge exchange. The lowest densities for b eam are ions occur during periods of purely residual outgassing from t he shuttle. Ion densities increase by a factor of 5 during waste water dumps. The highest densities occur during operation of the flash evap orator system when the pickup ion densities in daylight can exceed 10( 5) ions cm(-3), about 30% of the estimated ambient plasma density. We also present a nonlinear numerical analysis to study the stability of beam are generated plasma waves and explain electrostatic spectra meas ured during previous shuttle flights.