The American Society for Testing and Materials (ASTM) has published a new standard test method for characterizing time and temperature dependence of material outgassing kinetics and the deposition kinetics of outgassed species on surfaces at various temperatures. This new ASTM standard, E 1559,1 uses the quartz crystal microbalance (QCM) collection measurement approach. The test method was originally developed under a program sponsored by the U.S. Air Force Materials Laboratory to create a standard test method for obtaining outgassing and deposition kinetics data for spacecraft materials. Standardization by ASTM recognizes that the method has applications beyond aerospace. In particular, the method will provide data of use to the electronics, semiconductor, and high vacuum industries. This paper describes the ASTM E 1559 test method and presents some typical data. the paper also describes the Lockheed ASTM E 1559 test apparatus.
This paper describes the derivation ofcleanliness requirements and the development ofcontamination control procedures for the Space Infmred Telescope Facility (SLRTF), the fourth of the Great Observatories. SIRTF, scheduled for launch in December 2001 and designed to explore the infmreduniverse, will be placed into a heliocentric orbit and will perfonn background-limited imaging and spectroscopic measurements ofcelestial objects in the 3-180 pin spectral range. The main components of the facility are the three scientific instrument packages, a liquid helium dewar to maintain the instruments at 2 to 5 K, a telescope which is maintained at 5 K, and a spacecraft. The instruments/dewar assembly, known as the MIC, will be cooled before launch, while the telescope will be launched warm and will be cooled on orbit by a combination of radiation to space and Ilium boil off. SIRTF has several unique contamination control drivers and design challenges. The mission lifetime requirement of 2.5 years will be achieved by minimizing the thermal load on the telescope and helium dewar using very low emittance surfaces, most of which operate below the condensation temperature of water vapor, and are hence veiy vulnerable to emittance degradation due to contaminant deposition. Contaminant films and particles on optical surfaces will reduce optical throughput, increase off axis point source transmittance, and degrade the point spread function of the telescope and scientific instruments, and hence degrade the observatory perfonnance. Quantification ofthese effects is hamperedby the lack ofcontaminant optical effects data at long wavelengths (for species other than water) and uncertainty about the structure of cryolayers at temperatures less than 20 K. The operational temperatures of the SIRTF telescope and the cryostat (collectively known as the Cryogenic Telescope Assembly (CTA)) will be low enough to suppress equilibrium outgassing rates to negligible values, but outgassing of the telescope, baffle assembly, thennal insulation, etc. during initial cooldown is significant Assessment of molecular contaminant transport during this phase requires modeling the effect of transient source and deposition surface temperatures, as well as the measurement oftransient outgassing rates of materials at temperatures below ambient The study completed so far facilitates subsequent contamination analysis and control at the optical component level.
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