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Proceedings Paper

Comparison of stress-relief procedures for cryogenic aluminum mirrors
Author(s): Raymond G. Ohl; Michael P. Barthelmy; Said Wahid Zewari; Ronald W. Toland; Joseph C. McMann; David F. Puckett; John G. Hagopian; Jason E. Hylan; John Eric Mentzell; Ronald G. Mink; Leroy M. Sparr; Matthew A. Greenhouse; John W. MacKenty
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Paper Abstract

The Infrared Multi-Object Spectrograph is a facility instrument for the KPNO Mayall Telescope. IRMOS is a low- to mid-resolution, near-IR (0.8-2.5 um) spectrograph that produces simultaneous spectra of ~100 objects in its 2.8 × 2.0 arcmin field of view. The instrument operating temperature is ~80 K and the design is athermal. The bench and mirrors are machined from Al 6061-T651. In spite of its baseline mechanical stress relief, Al 6061-T651 harbors residual stress, which, unless relieved during fabrication, may distort mirror figure to unacceptable levels at the operating temperature (~80 K). Other cryogenic, astronomy instruments using Al mirrors have employed a variety of heat treatment formulae, with mixed results. We present the results of a test program designed to empirically determine the best stress relief procedure for the IRMOS mirrors. Identical test mirrors are processed with six different stress relief formulae from the literature and institutional heritage. After figuring via diamond turning, the mirrors are tested for figure error at room temperature and at ~80 K for three thermal cycles. The heat treatment procedure for the mirrors that yielded the least and most repeatable change in figure error is applied to the IRMOS mirror blanks. We correlate the results of our optical testing with heat treatment and metallographic data.

Paper Details

Date Published: 25 November 2002
PDF: 21 pages
Proc. SPIE 4822, Cryogenic Optical Systems and Instruments IX, (25 November 2002); doi: 10.1117/12.451762
Show Author Affiliations
Raymond G. Ohl, NASA Goddard Space Flight Ctr. (United States)
Michael P. Barthelmy, NASA Goddard Space Flight Ctr. (United States)
Said Wahid Zewari, NASA Goddard Space Flight Ctr. (United States)
Ronald W. Toland, NASA Goddard Space Flight Ctr. (United States)
Joseph C. McMann, ManTech International Corp. (United States)
NASA Goddard Space Flight Ctr. (United States)
David F. Puckett, NASA Goddard Space Flight Ctr. (United States)
John G. Hagopian, NASA Goddard Space Flight Ctr. (United States)
Jason E. Hylan, Swales Aerospace, Inc. (United States)
John Eric Mentzell, NASA Goddard Space Flight Ctr. (United States)
Ronald G. Mink, NASA Goddard Space Flight Ctr. (United States)
Leroy M. Sparr, NASA Goddard Space Flight Ctr. (United States)
Matthew A. Greenhouse, NASA Goddard Space Flight Ctr. (United States)
John W. MacKenty, Space Telescope Science Institute (United States)


Published in SPIE Proceedings Vol. 4822:
Cryogenic Optical Systems and Instruments IX
James B. Heaney; Lawrence G. Burriesci, Editor(s)

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