Teflon ® FEP (fluorinated ethylene propylene) surfaces on the Hubble Space Telescope (HST) have experienced significant degradation in mechanical properties during nearly ten years of exposure in the low Earth orbit environment. This paper describes results of mechanical properties testing of Teflon ® FEP materials exposed on HST for 9.7 years between launch and the third servicing mission (SM3A) and for 2.8 years between the second servicing mission (SM2) and SM3A. The results of tensile testing, bend testing and microscopic examination of crack morphology are described. The effects of post-retrieval heating and air compared with vacuum storage on the mechanical properties of the FEP surfaces are described as they significantly affect the interpretation of the results regarding the durability of FEP on HST. This paper provides comparisons of the properties of FEP surfaces retrieved during SM3A to previously reported results for FEP materials retrieved during the first servicing mission (SM1) and SM2. The environmental exposure conditions for the HST exposed materials are also described.

This paper describes the vacuum ultraviolet (VUV) radiation durability screening testing of thin (12.7-25.4 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 vapour deposited aluminium (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 at failure. Changes in the 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 of the polyimide materials tested. Changes in the 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.

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