ENVIRONMENTAL EXPOSURE CONDITIONS FOR TEFLON FEP ON THE HUBBLE SPACE TELESCOPE

摘要

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