Other
Scientific paper
Sep 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000spie.4096..129p&link_type=abstract
Proc. SPIE Vol. 4096, p. 129-137, Optical Systems Contamination and Degradation II: Effects, Measurements, and Control, Philip T
Other
Scientific paper
The Space Infrared Telescope Facility (SIRTF) is designed to explore the infrared universe. It will be placed into a heliocentric orbit and will perform background-limited imaging and spectroscopic measurements of celestial objects in the 3-180micrometers spectral range. Because the main components are operating at cryogenic temperatures, SIRTF has several unique contamination control drivers. This paper describes the analytical approaches to verify the requirements and to show that the requirements can be met. The particulate contamination analysis uses measured surface particle removal data and analytical random vibration surface interaction models to predict the particle distribution in an enclosure, such as the payload fairing, in an ascent vibroacoustic environment. The prediction shows an increase of percent area coverage (PAC) of the S tar Tracker front aperture window from 0.004$ (Level 200) to 0.475% (Level 572), assuming a surface random vibration level of 23 g-rms. The low-(epsilon) thermal control surface shows an increase of emissivity of 0.005 to 0.035, which meets the required value of 0.05 at end-of-life. In the molecular contamination analysis, the molecular transport kinetic (MTK) model was used with the cool-down temperature profiles to predict the molecular deposit during the early orbit period. An innovative sticking coefficient model that is a function of both the surface temperature and the mean dwell time, was used in the calculation. The results show that deposits of water condensation during this cool-down period are 18A on the exterior of the Cryogenic Telescope Assembly (CTA), 77A on the bus-side spacecraft shield, and negligible on the solar array shield and on the CTA-side spacecraft shield. Other molecular contamination sources, such as returned flux, interior molecular source, and nitrogen thruster plume, were also examined. The effects from these sources were found to be insignificant to the operations.
Lee Aleck L.
Perry Radford L.
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