EFFECT OF RAM EXPOSURE ON THE OPTICAL PROPERTIES OF POLYMERS IN SPACE

The temperature of spacecraft is influenced by the solar absorptance and thermal emittance of the external spacecraft polymer materials. Optical and thermal properties can degrade over time in the harsh low Earth orbital (LEO) space environment where polymers are exposed to radiation, thermal cycling, and atomic oxygen. Therefore, it is important to test their durability in the space environment. One objective of the Polymers Experiment was to determine the effect of long term LEO space exposure on the optical properties of various spacecraft polymers for each one's performance prediction purposes. This experiment was flown as part of the Materials International Space Station Experiment 7 (MISSE 7) mission on the exterior of the International Space Station (ISS) for 1.5 years. Samples were flown in the ram and zenith orientation, receiving different atomic oxygen and solar radiation exposures. Total diffuse reflectance and transmittance of seven ram and two zenith flight and corresponding control samples were obtained post-flight using a Cary 5000 UV-Vis-NIR Spectrophotometer. Integrated air mass zero solar absorptance (as) of the flight and control samples were computed from the total transmittance and reflectance, and compared. White Tedlar samples became brighter and decreased in as (up to 0.078), while polypropylene became darker and increased in ? by 0.050 with ram exposure. Results show that prolonged space exposure increases the solar absorptance of some materials. Knowing which polymers remain stable will benefit future spacecraft design.