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27 December 2001 Cryogenic optical testing results for the Subscale Beryllium Mirror Demonstrator (SBMD)
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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.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
James B. Hadaway, Joseph M. Geary, Patrick J. Reardon, Bruce R. Peters, H. Philip Stahl, Ron Eng, John W. Keidel, Jeffrey R. Kegley, Timothy Reed, and Donald A. Byrd "Cryogenic optical testing results for the Subscale Beryllium Mirror Demonstrator (SBMD)", Proc. SPIE 4451, Optical Manufacturing and Testing IV, (27 December 2001);


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