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Proceedings Paper

Cryogenic optical testing results for the Subscale Beryllium Mirror Demonstrator (SBMD)
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Paper Abstract

An Optical Testing System (OTS) has been developed to measure the figure and radius of curvature of Next Generation Space Telescope (NGST) developmental mirrors in a vacuum, cryogenic environment using the X-Ray Calibration Facility (XRCF) at Marshall Space Flight Center (MSFC). The OTS consists of a WaveScope Shack-Hartmann sensor from Adaptive Optics Associates as the main instrument and a Leica Disto Pro distance measurement instrument. Testing is done at the center of curvature of the test mirror and at a wavelength of 632.8 nm. The error in the figure measurement is <EQ(lambda) /13 peak-to-valley (PV). The error in radius of curvature is less than 5 mm. The OTS has been used to test the Subscale Beryllium Mirror Demonstrator (SBMD), a 0.532-m diameter spherical mirror with a radius of curvature of 20 m. SBMD characterization consisted of three separate cryogenic tests at or near 35 K. The first two determined the cryogenic changes in the mirror surface and their repeatability. The last followed cryo-figuring of the mirror. This paper will describe the results of these tests. Figure results will include full aperture results as well as an analysis of the mid-spatial frequency error results. The results indicate that the SBMD performed well in these tests with respect to the requirements of (lambda) /4 PV (full aperture), (lambda) /10 PV (mid-spatial, 1-10 cm), and +/- 0.1 m for radius of curvature after cryo-figuring.

Paper Details

Date Published: 27 December 2001
PDF: 12 pages
Proc. SPIE 4451, Optical Manufacturing and Testing IV, (27 December 2001); doi: 10.1117/12.453625
Show Author Affiliations
James B. Hadaway, Univ. of Alabama in Huntsville (United States)
Joseph M. Geary, Univ. of Alabama in Huntsville (United States)
Patrick J. Reardon, Univ. of Alabama in Huntsville (United States)
Bruce R. Peters, Univ. of Alabama in Huntsville (United States)
H. Philip Stahl, NASA Marshall Space Flight Ctr. (United States)
Ron Eng, NASA Marshall Space Flight Ctr. (United States)
John W. Keidel, NASA Marshall Space Flight Ctr. (United States)
Jeffrey R. Kegley, NASA Marshall Space Flight Ctr. (United States)
Timothy Reed, Ball Aerospace & Technologies Corp. (United States)
Donald A. Byrd, Tinsley Labs. (United States)


Published in SPIE Proceedings Vol. 4451:
Optical Manufacturing and Testing IV
H. Philip Stahl, Editor(s)

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