Review of Midcourse Space Experiment (MSX) Satellite QCM Contamination Results After 8 Years in Space

Abstract

The Midcourse Space Experiment (MSX) satellite was launched on April 24, 1996. This paper provides an update of the quartz crystal microbalance (QCM) data that have been accumulated since launch over eight years ago. This experiment is the only known experiment that has provided continuous contamination monitoring for this extended length of time, and it therefore provides a unique data set for assessing on-orbit spacecraft performance. The five QCMs on board the satellite have provided on-orbit data that are invaluable in characterizing contamination levels around the spacecraft and inside the SPIRIT III cryogenic telescope. One of the QCMs, the cryogenic QCM (CQCM), was located internal to the SPIRIT III cryogenic telescope adjacent to the primary mirror, and provided contamination accretion measurements during the 10-month lifetime of SPIRIT III. Real-time monitoring of contaminant mass deposition on the primary mirror was provided by this CQCM, which was cooled to the same temperature as the mirror (approximately 20K). Thermogravimetric analyses (TGAs) on the CQCM provided insight into the amount and species of contaminants condensed on the SPIRIT III primary mirror during various spacecraft activities. The four temperature-controlled QCMs (TQCMs) were mounted on external surfaces of the spacecraft for monitoring contaminant deposition. The TQCMs operated at approximately −50°C and were positioned strategically to monitor the silicone and organic contaminant flux arriving at specific locations. Updated time histories of contaminant thickness deposition for each of the QCMs are presented. Gradual contaminant thickness increase was observed during the first year in space. During the second year, the QCM frequencies (contaminant film thickness) began to decrease, with the time of decrease onset depending on QCM location. Possible explanations for this interesting behavior are discussed.