QCM flight measurements of contaminant films and their effect on midcourse space experiment (MSX) satellite optics

Abstract

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 has UV, visible, and infrared instruments including the SPIRIT 3 cryogenic telescope. It also has several contamination measuring instruments for measuring pressure, gas species, water and particulate concentrations and condensable gas species. A cryogenic quartz crystal microbalance (CQCM) and four temperature controlled microbalances (TQCMs) are part of this suite of contamination measuring instruments. 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. Real-time monitoring of contaminant mass deposition on the primary mirror is provided by the CQCM which is cooled to the same temperature as the mirror -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 -50°C and are positioned strategically to monitor the silicone and organic contaminant flux arriving at the UV and visible instruments, or coming from specific contaminant sources such as the solar panels. During the first week of flight operation, all QCMs recorded deposition in the 10-20 ng/cm2-day (1-2 A/day) range. These TQCM deposition rates have continuously decreased, and after 270 days mission elapsed time (MET), the rates have fallen to values between 0 and 0. 15 A/day depending on TQCM location. Thermogravimetric analyses (TGAs) on the CQCM and TQCMs have provided valuable insight into the amount and species of contaminants condensed.