Effects of radiation and thermal cycling on Teflon (R) FEP

Surfaces of the aluminized Teflon(R) FEP (fluorinated ethylene propylene) m ultilayer thermal insulation on the Hubble Space Telescope (HST) were found to be cracked and curled in some areas at the time of the second servicing mission (SM2) in February 1997, 6.8 years after HST was deployed in low Ea rth orbit (LEO). In an effort to understand what elements of the space envi ronment might cause such damage, pristine second-surface aluminized Teflon( R) FEP was tested for durability to various types of radiation, to thermal cycling and to radiation followed by thermal cycling. Types of radiation in cluded synchrotron vacuum ultraviolet and soft x-ray radiation, simulated s olar flare x-ray radiation, electrons and protons. Thermal cycling was cond ucted in various temperature ranges to simulate HST orbital conditions for Teflon(R) FEP. Results of tensile testing of the exposed specimens showed t hat exposure to high fluences of radiation caused degradation in tensile pr operties of FEP. However, exposure to radiation alone in exposures comparab le to those experienced by HST did not produce reduction in ultimate tensil e strength and elongation of Teflon(R) similar to that observed for HST-ret rieved aluminized Teflon(R). Synergism of radiation exposure and thermal cy cling was evident in the results of three experiments: thermal cycling foll owing electron and proton irradiation, thermal cycling following x-ray expo sure, and additional thermal cycling of a sample retrieved from HST. Howeve r, irradiation and thermal cycling with comparable HST SM2 exposure conditi ons did not produce the degradation observed in the FEP material retrieved during HST SM2.