MSX Satellite Flight Measurements of Contaminant Deposition on a CQCM and on TQCMs

The Midcourse Space Experiment MSX is a Ballistic Missile Defense Organization BMDO demonstration and validation satellite program that has both defense and civilian applications. MSX was launched April 24, 1996, and has UV, visible, and infrared instruments including the SPIRIT 3 Space Infrared Imaging Telescope cryogenic telescope. It also has several contamination measuring instruments for measuring pressure, gas species, water and particulate concentrations and condemnable gas species. A cryogenic quartz crystal microbalance CQCM and four temperature-controlled microbalances TQCMs are part of this suite of contamination measuring instruments on board the satellite. This paper describes some of the flight QCM data obtained and analyzed to date. The CQCM is located internal to the SPIRIT 3 cryogenic telescope and is mounted adjacent to the primary mirror. Monitoring of contaminant mass deposition on the primary mirror is being provided by the CQCM, which is cooled to the same temperature as the mirror - approx. 20 K. The four TQCMs are mounted on the outside of the spacecraft and monitor contaminant deposition on the external surfaces. The TQCMs operate at approx. -50 C and are positioned strategically to monitor the silicone and organic contaminant flux arriving at specific locations, such as near to the UV instruments, or coming from specific contaminant sources such as the solar panels. Time histories of contaminant thickness deposition for each of the QCMs are presented. During the first week of flight operation, all QCMs recorded deposition in the 10-20 ngcm 2-day 1-2 ang.day range. These TQCM deposition rates have continuously decreased, and after 100 days into the mission the measured rates have fallen to values between 0 and 0.2 ang.day depending on TQCM location.