Automated Plume Sentry Observations During International Space Station Thermal Control System Venting

Abstract

Contamination from outgassed materials, venting, leaks, and impinging thruster plumes can cause deleterious effects to sensitive experiments on the International Space Station. In low Earth orbit, intermolecular collisions between neutral contaminants and ions in the ambient ionospheric environment result in an elevation in the local charged particle density through a process called charge exchange (CEX). Of particular concern to spacecraft engineers is the acceleration of these ionized neutrals to sensitive negatively charged spacecraft surfaces. The increase in plasma density due to CEX can be readily measured using plasma diagnostics such as electrostatic energy analyzers. These instruments are capable of monitoring charged particle flux and are sensitive enough to measure small changes in local density, thus allowing for the detection of CEX contaminants. The automated plume sentry (APS) is one such instrument, and it has successfully detected CEX plasma generated by the planned ammonia venting of the external active thermal control system. The data collected by the APS will support the development of improved computational models to predict the propagation of outgassed materials and plumes in the ionosphere and complex gas–surface interactions resulting in spacecraft surface contamination.