20 September 2000 Measurement of long-term outgassing from the materials used on the MSX spacecraft
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The Midcourse Space Experiment (MSX) spacecraft was specifically designed and processed to minimize contamination. This spacecraft represents a best case scenario of spacecraft induced environment. The contamination instrument suite consisted of 10 sensors for monitoring the gaseous and particulate environment. The Total Pressure Sensor (TPS) has continuously measured the ambient local pressure surrounding MSX since its launch on April 24, 1996. The sensor's primary goal was to monitor the early mission (less than one week) ambient pressure surrounding the spacecraft's optical telescopes and to indicate when environmental conditions were acceptable for opening the protective covers. However, the instrument has illustrated that it is quite robust and has successfully measured the long-term decay of the pressure environment. The primary constituent of the atmosphere is water outgassed from the thermal blankets of the spacecraft. The water-induced environment was expected to rapidly decay over the first few months to levels more closely approaching the natural environment. The data generally shows decay toward this level, however, the pressure is quite variable with time and can be influenced by discrete illumination and spacecraft orbital events. Several experiments conducted yearly indicate that the thermal blankets retain significant quantities of water. The local pressure due to water vapor is shown to increase by a factor of 100 from direct solar illumination. Moreover, the multi-layer construction of the blankets causes them to form a deep reservoir that continues to be a source of water vapor 3+ years into the mission. We will present pressure data from several experiments, each separated by one orbital year, that exhibit these water vapor induced pressure busts. The decay and longevity of these bursts will also be discussed.
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Mark T. Boies, B. David Green, Gary E. Galica, O. Manuel Uy, Richard C. Benson, David M. Silver, Bob E. Wood, Jeffrey C. Lesho, David F. Hall, James S. Dyer, "Measurement of long-term outgassing from the materials used on the MSX spacecraft", Proc. SPIE 4096, Optical Systems Contamination and Degradation II: Effects, Measurements, and Control, (20 September 2000); doi: 10.1117/12.400834; https://doi.org/10.1117/12.400834

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