Effect of Air and Vacuum Storage on the Tensile Properties of X-Ray Exposed Aluminized-FEP

Metallized Teflon® FEP (fluorinated ethylene propylene), a common spacecraft thermal control material, which forms the exterior layer of the Hubble Space Telescope (HST) has become embrittled and suffers from extensive cracking. Teflon® samples retrieved during Hubble servicing missions and from the Long Duration Exposure Facility (LDEF) indicate that there may be continued degradation in the tensile properties over time. An investigation has been conducted to evaluate the effect of air and vacuum storage on the mechanical properties of x-ray exposed FEP. Aluminized-FEP (Al-FEP) tensile samples were irradiated with 15.3 kV Cu x-rays and stored in air or under vacuum for various time periods. Tensile data indicate that samples stored in air display larger decreases in their tensile properties than for samples stored under vacuum. Air-stored samples developed a hazy appearance, which corresponded to a roughening of the aluminized surface. Optical property changes were also characterized. These findings indicate that air exposure plays a role in the degradation of irradiated FEP, therefore proper sample handling and storage is necessary with materials retrieved from space.