Return flux experiment REFLEX: spacecraft self-contamination

On-orbit, self-contamination of a spacecraft is a concern facing instrument and spacecraft designers. While on the Earth, gases adsorb onto spacecraft surfaces. These gases are later released when placed in the vacuum of space. The rate at which the emitted gases are returned to the spacecraft by collisions with other gaseous molecules is known as the return flux. Models predicting the amount of gas released by a spacecraft that is returned to itself do exist, but these models have had very limited experimental testing. We describe a flight experiment designed to provide a test of these models and the analysis of the data obtained by that experiment. The experiment flew on a 1996 space shuttle mission and provided in-situ testing of the return flux models. Analysis of the limited data obtained by the experiment has determined the return flux is primarily due to collisions with the ambient atmosphere and not collisions with other gases released by the spacecraft. Limited measurements of the ambient atmosphere were also made.