Ground-based testing of replacement thermal control materials for the Hubble Space Telescope

The mechanical and optical properties of the metallized Teflon(R) FEP therm al control materials on the Hubble Space Telescope (HST) have degraded over the nearly seven years the telescope has been in orbit. Given the damage t o the outer layer of the multilayer insulation (MLI) blanket that was appar ent during the second servicing mission (SM2), the decision was made to rep lace the outer layer during subsequent servicing missions. A Failure Review Board was established to investigate the damage to the MLI: and identify a replacement material. The replacement material had to meet the stringent t hermal requirements of the spacecraft and maintain mechanical integrity for at least ten years. Ten candidate materials were selected and exposed to ten-year HST-equivalen t doses of simulated orbital environments. Samples of the candidates were e xposed sequentially to low- and high-energy electrons and protons, atomic o xygen, x-ray radiation, ultraviolet radiation and thermal cycling. Followin g the exposures, the mechanical integrity and optical properties of the can didates were investigated using optical microscopy, scanning electron micro scopy (SEM), a laboratory portable spectroreflectometer (LPSR) and a Lambda 9 spectroreflectometer. Based on the results of these simulations and anal yses, the Failure Review Board selected a replacement material and two alte rnatives that showed the highest likelihood Of providing the requisite ther mal properties and surviving for ten years in orbit.