Changes in Optical and Thermal Properties of the MISSE 2 Peace Polymers and Spacecraft Silicones
Waters DL, et al. (2009). "Changes in Optical and Thermal Properties of the MISSE 2 Peace Polymers and Spacecraft Silicones." 11th International Symposium on Materials in a Space Environment
This paper documents optical and thermal properties of polymers and silicones from the Materials International Space Station Experiment 2 (MISSE 2) Polymer Erosion and Contamination Experiment (PEACE) Polymers experiment and from the MISSE 4 Spacecraft Silicones experiment. PEACE included forty-one polymer samples that were exposed to the low Earth orbit (LEO) environment on the exterior of the International Space Station (ISS) for almost four years. The Spacecraft Silicones experiment is comprised of eight DC 93-500 silicone samples manufactured by Dow Corning, four of which were flown as part of MISSE 2, and four of which were flown as part of MISSE 4. MISSE 4 was exposed to the space environment on the exterior of ISS for 1 year. Both the PEACE Polymers and the Spacecraft Silicone experiments were exposed to atomic oxygen (AO) along with solar and charged particle radiation while in LEO. The majority of the PEACE samples are comprised of numerous thin film layers stacked together. Because many of the PEACE polymers are commonly used for spacecraft applications, their optical and thermal properties are very important. DC 93-500 silicone is a popular spacecraft optical adhesive, often used for photovoltaic applications, hence changes in optical properties, particularly transmittance, due to LEO exposure is very important. Changes in optical and thermal properties due to LEO environmental exposure have been analyzed for all of the materials that could be measured. Due to the long duration space exposure, several of the MISSE 2 samples were too degraded for their properties to be measured. Total and diffuse reflectance, and total and diffuse transmittance, were measured as a function of wavelength and compared with non-exposed control samples. Specular reflectance and specular transmittance were then computed. Thermal emittance data was also generated for numerous samples. For most samples, specular and diffuse reflectance characteristics changed greatly upon directed LEO atomic oxygen exposure. Typically, there is a decrease in specular reflectance with an increase in diffuse reflectance. These optical property changes are relevant to glare issues, Fresnel lens photovoltaic concentrator power loss issues and issues with spatial variations in the thermal load on a spacecraft. The wavelength dependant data also allows computation of the change in solar absorptance (αs) and thermal emittance, which is critical for predicting thermal control characteristics of a spacecraft. A summary of the MISSE 2 PEACE Polymers and Spacecraft Silicones experiments, the specific materials flown, optical and thermal property measurement procedures, and the optical and thermal property data are presented.