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 ≤λ/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 λ/4 PV (full aperture), λ/10 PV (mid-spatial, 1-10 cm), and ±0.1 m for radius of curvature after cryo-figuring.

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NASA Marshall Space Flight Center (MSFC) has maintained and operated a world-class x-ray optics and detector testing facility known as the X-ray Calibration Facility (XRCF) since the mid 1970's. The ground testing and calibration of the Chandra X-ray Observatory optics and detectors were successfully completed at the XRCF in 1997. In 1999, the facility was upgraded in preparation for cryogenic testing of lightweight telescope mirrors without compromising the existing x-ray testing capability. A gaseous Helium (He) cooled enclosure or shroud capable of 20 degrees Kelvin and vibration isolated instrumentation mount were added to the existing facility. A precision remote-control five-axis motion mirror support was modified to operate under cryogenic conditions. Mirrors with diameters as large as two meters, and radii of curvature up to twenty meters can be accommodated in the He shroud. Optical wavefront measuring instrumentation includes a ShackHartmann wavefront sensor, a point diffraction interferometer, a point spread function measuring device, and a radius of curvature measuring instrument. These instruments can provide accurate measurements of the mirror under test. A vibration insensitive phase shifting interferometer is planned for future optical testing.

The GoidHelox Solar X-Ray Telescope underwent several tests during the years of 1997-1999, and continues through the testing phase of the project. The instrument itself, a solar telescope to ride on board the Space Shuttle, is designed to photograph the sun in soft x-ray wavelengths between 171A to 181A. Critical to its success, many tests are required to insure safety, robustness, and overall accuracy of the telescope during its mission. Among these are shake table tests, optical tests, vacuum integrity, and thermal analysis. This paper describes the GoldHelox project including its current status as a mission, the tests performed on the instrument to date, and the tests pending.

Marshall Space Flight Center has modified the X-ray Calibration Facility to test Next Generation Space Telescope developmental mirrors at cryogenic temperatures (35 Kelvin) while maintaining capability for performance testing of x-ray optics and detectors.