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Comparison of Stress Relief Procedures for Cryogenic Aluminum MirrorsThe Infrared Multi-Object Spectrograph (IRMOS) is a facility instrument for the Kitt Peak National Observatory Mayall Telescope (3.8 meter) and an engineering prototype for a potential design for the Next Generation Space Telescope/Multi-Object Spectrograph. IRMOS is a low-to mid-resolution (R = lambda/delta-lambda = 300-3800), near-IR (0.8-2.5 micron) spectrograph which produces simultaneous spectra of approximately 100 objects in its 2.8 x 2.0 arcmin field of view using a commercial MEMS multimirror array device. The instrument operating temperature is 80 K and the design is athermal --- the optical bench and mirrors are machined from aluminum 6061-T651. In spite of its baseline mechanical stress relief, aluminum 6061-T651 harbors some residual stress, which, unless relieved during fabrication, may relieve and distort mirror figure to unacceptable levels at the operating temperature. Other cryogenic instruments using aluminum mirrors for both ground-based and space IR astronomy 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 with spherical and flat optical prescriptions are processed with five different heat treatment formulae from the literature and compared to samples with out any additional processing. After figuring via diamond turning, the mirrors are tested for figure error and radius of curvature at room temperature and at 80 K for several thermal cycles. The heat treatment procedure for the mirrors that yielded the least and most repeatable change in figure error and radius is applied to the IRMOS mirror blanks. We correlate the results of our optical testing with heat treatment and metallographic data.
Document ID
20020061280
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Ohl, Raymond G.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Barthelmy, Michael P.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Zewari, S. Wahid
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Toland, Ronald
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Mink, Ronald
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Mentzell, J. Eric
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Greenhouse, Matthew A.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
McMann, Joseph C.
(ManTech, Inc. Greenbelt, MD United States)
Hylan, Jason
(Swales Aerospace Beltsville, MD United States)
Hagopian, John G.
(SOWILO Networks Columbia, MD United States)
Krebs, Carolyn
Date Acquired
August 20, 2013
Publication Date
January 1, 2002
Subject Category
Optics
Meeting Information
Meeting: SPIE Conference
Location: Seattle, WA
Country: United States
Start Date: July 8, 2002
End Date: July 11, 2002
Sponsors: International Society for Optical Engineering
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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