Environmental exposure conditions for Teflon fluorinated ethylene propylene on the Hubble space telecope

摘要

The outer layer of Tdeflon fluorinated ethylene propylene (FEP) multi-layer insulation (MLI) on the Hubble Space Telescope (HST) was observed to be significantly cracked at the time of the Second HST Servicing Mission (SM2),6.8 years affter HST was launched into low Earth orbit (LEO).Comparatively minor embrittlement and cracking were also observed in the FEP materials retrieved from solar-facing surfaces on the HST at the time of the First Servicing Mission (3.6 years exposure).After SM2,a failure review board was convened to address the problem of degradation of MLI on the HST.In order for this board to determine possible degradation mechanism,it was necessary to consider all environmental consituents to which the FEP MLI surfaces were exposed.Based on measurements and various models,the environmental exposure conditions for the FEP surfaces on the HST were estimated,including: the number and temperature ranges of thermal cycles; equivalent sun hours; fluence and absorbed radiation dose of x0rays,trapped protons and electrons and plasma electrons and protons; and atomic oxygen (AO) fluence. This paper presents the environmental exposure conditions of FEP on the HST,briefly describing the possible roles of the environmental factors on the observed FEP embrittlement and providing references to the published works which describe in detail testing and analysis related to FEP degradation on the HST.