Mechanical properties of Teflon((R)) FEP retrieved from the hubble space telescope

Teflon (R) FEP (fluorinated ethylene propylene) surfaces on the Hubble Spac e Telescope (HST) have experienced significant degradation in mechanical pr operties during nearly ten years of exposure in the low Earth orbit environ ment. This paper describes results of mechanical properties testing of Tefl on (R) FEP materials exposed on HST for 9.7 years between launch and the th ird servicing mission (SM3A) and for 2.8 years between the second servicing mission (SM2) and SM3A. The results of tensile testing, bend testing and m icroscopic examination of crack morphology are described. The effects of po st-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. T his paper provides comparisons of the properties of FEP surfaces retrieved during SM3A to previously reported results for FEP materials retrieved duri ng the first servicing mission (SM1) and SM2. The environmental exposure co nditions for the HST exposed materials are also described.