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Next Generation Space Telescope Sunshield Materials Titles |
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Titles:
Dever, J., Semmel, C., Edwards, D., Messer, R., Peters, W., Carter, A., and Puckett, D., “Radiation Durability of Candidate Polymer Films for the Next Generation Space Telescope Sunshield,” AIAA 2002-1564, April 2002. Also appears as: NASA TM-2002-211508, April 2002. The Next Generation Space Telescope (NGST), anticipated to be launched in 2009 for a 10-year mission, will make observations in the infrared portion of the spectrum to examine the origins and evolution of our universe. Because it must operate at cold temperatures in order to make these sensitive measurements, it will use a large, lightweight, deployable sunshield, comprised of several polymer film layers, to block heat and stray light. This paper describes laboratory radiation durability testing of candidate NGST sunshield polymer film materials. Samples of fluorinated polyimides CP1 and CP2; and a polyarylene ether benzimidazole, TOR-LM™, were exposed to 40 keV electron and 40 keV proton radiation followed by exposure to vacuum ultraviolet (VUV) radiation in the 115-200 nm wavelength range. Samples of these materials were also exposed to VUV without prior electron and proton exposure. Samples of polyimides Kapton® HN, Kapton® E, and Upilex-S were exposed to electrons and protons, only, due to limited available exposure area in the VUV facility. Exposed samples were evaluated for changes in solar absorptance and thermal emittance and mechanical properties of ultimate tensile strength and elongation at failure. Data obtained are compared with previously published data for radiation durability testing of these polymer film materials.
This paper describes the vacuum ultraviolet (VUV) radiation durability screening testing of thin (12.7 to 25.4 µm) polyimide films proposed for use on the Next Generation Space Telescope (NGST) sunshield. Materials included in this screening test were Kapton®E, Kapton®HN, Upilex®S, CP1, CP1 with vapor deposited aluminum (VDA) on its back surface, and CP2 with a VDA coating on its back surface. Samples were exposed to approximately 1000 equivalent sun hours (ESH) of VUV radiation and examined for changes in solar absorptance, thermal emittance, ultimate tensile strength, and elongation-to-failure. Changes in solar absorptance were observed for some materials, and additionally, significant changes in spectral reflectance were observed in the ultraviolet to visible wavelength region for all polyimide materials tested. Changes in ultimate tensile strength and elongation at failure were within the experimental uncertainty for all samples. Longer exposures are needed to verify the observed trends and to develop performance predictions for these materials on the NGST sunshield.
A test program has been implemented to evaluate candidate thin
film materials for the sun-facing layer of the Next Generation Space
Telescope (NGST) sunshield. Various polymers are being tested to
determine if any
can survive the radiation environment of the proposed NGST orbit (the
second sun-Earth Lagrangian point, or L2). This testing will
characterize the mechanical and thermal properties before and after
exposure to a simulated NGST sunshield environment. In addition,
because the sunshield will be folded and stowed before launch, the
candidate materials will be folded, stowed, and unfolded (deployed) to
determine if they can survive this type of handling and storage. Based
on the results of this testing, candidates will be selected for further
development and testing. Future development will include the addition
of
optical coatings, rip-stop for tear resistance, and seaming techniques. |
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