ENERGY-DISTRIBUTIONS OF THRUSTER PICKUP IONS DETECTED BY THE SHUTTLE POTENTIAL AND RETURN ELECTRON EXPERIMENT DURING TSS-1

Instrumentation to monitor the shuttle environment during the Tethered Satellite System (TSS 1) mission included the Shuttle Potential and R eturn Electron Experiment (SPREE) and the Quadrupole Ion-Neutral Mass Spectrometer (QINMS). SPREE measured fluxes of electrons and ions with energies between 10 eV and 10 keV; QINMS monitored neutral and ion sp ecies close to the shuttle. We report on energy distributions of picku p ions detected during and after thruster emissions while the shuttle' s velocity vector was nearly perpendicular to the Earth's magnetic fie ld. With SPREE looking in the ram direction and almost perpendicular t o the magnetic field, fluxes > 10(11) ions cm(-2) s(-1) sr(-1) were de tected in the 10-to-60-eV energy range. Both prompt and prolonged ion flux enhancements were recorded. The prolonged fluxes lasted many seco nds after the initiating thruster turned off. Only when thrusters fire d close to the magnetic field direction were no pickup-ion flux enhanc ements detected. The SPREE measurements are compared with the predicti ons of a simple two-dimensional model of collisionless pickup-ion traj ectories. Using the distribution of ion species recorded by QINMS, the model explains the main features of the ion energy spectra measured b y SPREE. Comparison of the model with data also indicates that strong scattering of ejected materials must occur almost immediately after th ruster emission and later between the time of pickup-ion creation and detection of the increased ion flux by SPREE.