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Proceedings Paper

Cryogenic emittance measurement and its accuracy for the James Webb space telescope
Author(s): Chuen Or; Warren Tolson; Stuart Glazer; Mark Kobel; Edward Packard
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Paper Abstract

NASA's James Webb Space Telescope-Integrated Science Instrument Module (JWST-ISIM) radiators and structures operate in the 30 to 40 K range. There is limited emittance data for coatings of interest in this temperature range. Calorimetric emittance tests performed at Goddard Space Flight Center in the past have used a transient technique, which results in large uncertainties (typically > +/-30%) at the lowest temperatures. These large uncertainties would practically require use of overly conservative emissivities in radiator sizing, which would in turn pose unnecessary area and mass penalties. There is thus a strong incentive to make highly accurate emittance measurements. A special liquid helium cryogenic facility was fabricated for this purpose, and a series of thermal balance tests were subsequently performed at NASA/GSFC to measure the emittance of selected ISIM coatings accurately at temperatures down to 25K. This paper discusses the test methodology, and the analytical methods used to calculate the emittance and its accuracy from the measured data. Preliminary results show that for relatively high emittance coatings, typical measurement accuracies at 30 K approach +/- 5%.

Paper Details

Date Published: 25 August 2005
PDF: 11 pages
Proc. SPIE 5904, Cryogenic Optical Systems and Instruments XI, 59040H (25 August 2005); doi: 10.1117/12.624020
Show Author Affiliations
Chuen Or, Swales Aerospace (United States)
Warren Tolson, Swales Aerospace (United States)
Stuart Glazer, NASA Goddard Space Flight Ctr. (United States)
Mark Kobel, NASA Goddard Space Flight Ctr. (United States)
Edward Packard, NASA Goddard Space Flight Ctr. (United States)

Published in SPIE Proceedings Vol. 5904:
Cryogenic Optical Systems and Instruments XI
James B. Heaney; Lawrence G. Burriesci, Editor(s)

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