Hubble Space Telescope Metallized Teflon ® FEP thermal Control Materials: On-Orbit Degradation and Post-Retrieval Analysis

Abstract

During the Hubble Space Telescope (HST) second servicing mission (SM2), degradation of unsupported Teflon ® FEP (fluorinated ethylene propylene), used as the outer layer of the multilayer insulation (MLI) blankets, was evident as large cracks on the telescope light shield. A sample of the degraded outer layer was retrieved during the mission and returned to Earth for ground testing and evaluation. The results of the Teflon ® FEP sample evaluation and additional testing of pristine Teflon ® FEP led the investigative team to theorize that the HST damage was caused by thermal cycling with deep-layer damage from electron and proton radiation which allowed the propagation of cracks along stress concentrations, and that the damage increased with the combined total dose of electrons, protons, ultraviolet and x-ray radiation along with thermal cycling. This paper discusses the testing and evaluation of the retrieved Teflon ® FEP.

Degradation of SpaceSuit Fabrics in Low Earth Orbit

“…The AO erosion yield for FEP films has been determined previously to be 2.00×10 -25 cm 3 /atom (Ref. 12).…”

Small-scale mechanical characterization of space-exposed fluorinated ethylene propylene recovered from the Hubble Space Telescope

“…The outermost layer of MLI is made of 127 µm thick fluorinated ethylene propylene (FEP) with a 100 nm thick vapor deposited aluminum layer (Al-FEP) on the inner face which helps to shield sub-layers of the MLI. Based on observations during previous servicing missions and ground analysis of returned material, this outer layer of Al-FEP is known to degrade in the on-orbit environment [1] [2] . In May 2009 during Hubble Servicing Mission 4, two full MLI blankets from equipment Bay 5 and Bay 8 of the telescope were replaced and returned to earth.…”

“…These Al-FEP blankets had been in low earth orbit since Hubble's deployment, with regions varying in exposure to solar radiation, thermal cycling, space debris, and atomic oxygen. Previous NASA studies [1][2][3] [4] were performed to understand the combined effect of temperature cycling and solar radiation on the Al-FEP.…”

“…Furthermore, atomic oxygen is known to react with the space-exposed FEP at the surface, resulting in a thickness reduction [9][15] [16] . Full details on the environmental factors of low earth orbit are outlined by Dever et al [16] , and it has been shown that strength and ductility are influenced by a combination of these factors [1][2] [3] .…”

Exposure of polymer film thermal control materials on the Materials International Space Station Experiment (MISSE)

“…2 Space environmental effects that can cause damage to polymers include solar ultraviolet radiation, solar flare x-rays, solar wind electrons and protons trapped in Earth's magnetic field, temperature effects, and low Earth orbit AO. Spacecraft surfaces may experience significant temperature excursions during each orbit due to the transitions of the spacecraft between sunlight and shadow.…”