Energy distributions of thruster pickup ions detected by the Shuttle Potential and Return Electron Experiment during TSS 1

Abstract

Instrumentation to monitor the shuttle environment during the Tethered Satellite System (TSS 1) mission included the Shuttle Potential and Return 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 species close to the shuttle. We report on energy distributions of pickup ions detected during and after thruster emissions while the shuttle's velocity vector was nearly perpendicular to the Earth's magnetic field. With SPREE looking in the ram direction and almost perpendicular to the magnetic field, fluxes >1011 ions cm−2 s−1 sr−1 were detected in the 10‐to‐60‐eV energy range. Both prompt and prolonged ion flux enhancements were recorded. The prolonged fluxes lasted many seconds after the initiating thruster turned off. Only when thrusters fired close to the magnetic field direction were no pickup‐ion flux enhancements detected. The SPREE measurements are compared with the predictions of a simple two‐dimensional model of collisionless pickup‐ion trajectories. Using the distribution of ion species recorded by QINMS, the model explains the main features of the ion energy spectra measured by SPREE. Comparison of the model with data also indicates that strong scattering of ejected materials must occur almost immediately after thruster emission and later between the time of pickup‐ion creation and detection of the increased ion flux by SPREE.