Effect of Solar Exposure on the Atomic Oxygen Erosion of Hubble Space Telescope Aluminized-Teflon Thermal Shields

Abstract

When exposed to low Earth orbit (LEO) environment, external spacecraft materials degrade due to radiation, thermal cycling, micrometeoroid and debris impacts, and interaction with atomic oxygen (AO). Collisions between AO and spacecraft can result in oxidation of external spacecraft surface materials, which can lead to erosion and severe structural and/or optical properties deterioration. It is therefore essential to understand the AO erosion yield (Ey), the volume loss per incident oxygen atom (cm³/atom) of polymers to assure durability of spacecraft materials. The objective of this study was to determine whether solar radiation exposure can increase the rate of AO erosion of polymers in LEO. The material studied was a section of aluminized-Teflon® fluorinated ethylene propylene (Al-FEP) thermal shield exposed to space on the Hubble Space Telescope (HST) for 8.25 years. Retrieved samples were sectioned from the circular thermal shield and exposed to ground laboratory thermal energy AO. The results indicate that the average Ey of the solar facing HST Al-FEP was 1.9 × 10⁻²⁴ cm³/atom, while the average Ey of the anti-solar HST Al-FEP was 1.5 × 10⁻²⁴ cm³/atom. The Ey of the pristine samples was 1.6 to 1.7 × 10⁻²⁴ cm³/atom. These results indicate that solar exposure affects the post-flight erosion rate of FEP in a plasma asher. Therefore, it likely affects the erosion rate while in LEO.