Space environment exposure effects on polyimide aerogels

Abstract

As part of the Materials International Space Station Experiment (MISSE) missions, polyimide aerogel samples as prepared and atomic oxygen plasma treated with bulk densities of 0.09 and 0.15 g/cm³ were exposed on the exterior of the International Space Station (ISS) during MISSE-9, 12, and 15 missions for 0.77, 0.89, and 0.44-year direct space exposure times, respectively. The aerogel samples were synthesized from a combination of the diamines 1,3-bis(4-aminophenoxy)-2,2-dimethylpropane (BAPN) and 2,2′-dimethylbenzidine (DMBZ), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 1,3,5-triaminophenoxybenzene (TAB) as the crosslinker. At low Earth orbit (LEO), spacecraft are subjected to extreme environmental conditions such as thermal cycling, solar radiation, cosmic rays, solar wind charged particles and atomic oxygen (AO). A post-flight analysis of aerogel physical, chemical, mechanical, thermal and optical properties were performed using a series of non-destructive techniques. The polyimide aerogels exhibited a notably higher AO erosion yield compared to nonporous Kapton H or HN polyimides, attributed to their order of magnitude lower bulk density and much higher surface area. Yet, the post-flight characterizations reveal no significant degradation in material properties. For example, in terms of material’s structural integrity, the post-flight Young’s moduli at both low and high densities were not statistically changed. Similar observations were obtained for thermal and optical properties in terms of changes in the materials’ thermal conductivity and solar absorptance. The aerogel flight samples with pre-flight surface treatments using atomic oxygen plasma showed a higher susceptibility to the LEO environment compared to as-prepared aerogel flight samples. Despite their high AO erosion yield, this study shows that polyimide aerogels maintain remarkable stability throughout extended space missions and explorations and therefore can be considered as a space-rated material.