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Proceedings Paper

Selection of infrared black(s) for the Space Infra-Red Telescope Facility (SIRTF): a surface-by-surface performance comparison
Author(s): Ann St. Clair Dinger
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Paper Abstract

SIRTF, the Space Infrared Telescope Facility, is planned to be the final one of NASA's four great observatories. It is a cryogenically cooled telescope designed to perform background- limited observations at all wavelengths between 2 and 220 micrometers . This stringent straylight requirement necessitates the use of infrared black coatings on all non-optical telescope surfaces. In order to make an informed decision, the SIRTF Study Office supported a long- range program to characterize the performance of a variety of black coatings over the full SIRTF wavelength range. Measurements of both specular reflectance and BRDF made by Sheldon Smith were incorporated into a model that predicts the blacks' BRDF coefficients at other wavelengths. The restrahlen reflectance peaks of Martin Black and Martin Infrablack at 2.2 and 5.4 micrometers are included in the model. An APART analysis of the current SIRTF telescope design was performed at wavelengths of 2.2, 3.5, 12.5, 60, and 200 micrometers . Evaluation of the relative performances of Martin Optical Black and Ames 24E2 on several critical surfaces led to the conclusion that the SIRTF straylight rejection could be enhanced by selecting different coatings for different surfaces. A very diffuse black is best on the mirror stops and secondary support struts, while a specular black could be a better choice for the vaned telescope barrel. Many coatings that are black and diffusely scattering at short wavelengths become quite bright and specular at long wavelengths. Extreme caution must be taken when using a black that becomes specular on any surface that can be seen from the telescope plane.

Paper Details

Date Published: 7 October 1994
PDF: 10 pages
Proc. SPIE 2260, Stray Radiation in Optical Systems III, (7 October 1994); doi: 10.1117/12.189213
Show Author Affiliations
Ann St. Clair Dinger, NASA Ames Research Ctr. and Sterling Federal Systems, Inc. (United States)

Published in SPIE Proceedings Vol. 2260:
Stray Radiation in Optical Systems III
Robert P. Breault, Editor(s)

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