Metallized Teflon fluorinated ethylene propylene (PEP) thermal control material on the Hubble Space Telescope (RST) is degrading in the space environment. Teflon PEP insulation was retrieved during servicing missions, which occurred in 1993, 1997 and 1999. During the second servicing mission (SM2), the 5 mil aluminized-PEP (Al-PEP) outer layer of multilayer insulation (MLI) covering the telescope was found to be cracked in many locations around the telescope. Teflon PEP retrieved during SM2 was more embrittled than the PEP retrieved 2.8 years later from a different location, during the third servicing mission (SM3A). Studies have been conducted to understand the degradation of PEP on RST, and the difference in the degree of degradation of PEP from each of the servicing missions. The retrieved SM2 material experienced a higher temperature extreme during thermal cycling (200 deg C) than the first servicing mission (SM1) and SM3A materials (upper temperature of 50 deg C), therefore an investigation on the effects of heating PEP was also conducted. Samples of pristine PEP and SM1, SM2 and SM3A retrieved PEP were heated to 200 degC and evaluated for changes in properties. Heating at 130 deg C was also investigated because PEP bi-stem thermal shields are expected to cycle to a maximum temperature of 130 deg C on-orbit. Tensile, density, x-ray diffraction crystallinity and differential scanning calorimetry data were evaluated. It was found that heating pristine PEP caused an increase in the density and practically no change in tensile properties. However, when as-retrieved space samples were heated, the density increased and the tensile properties decreased. Upon heating, all samples experienced an increase in crystallinity, with larger increases in the space-exposed PEP. These results indicate that irradiation of PEP in space causes chain scission, resulting in embrittlement, and that excessive heating allows increased mobility of space-environment-induced scissioned chains. Thermal exposure was therefore found to have a major impact on the extent of embrittlement of PEP on HST.
Thermal contributions to the degradation of teflon FEP on the Hubble space telescope
2001
20 Seiten, 13 Bilder, 9 Tabellen, 10 Quellen
Aufsatz (Konferenz)
Englisch
Degradation of Hubble Space Telescope aluminized-Teflon bi-stem thermal shields
Tema Archiv | 2008
|Mechanical properties of teflon FEP retrieved from the Hubble space telescope
Tema Archiv | 2001
|