DESIGN OF LOW EARTH ORBIT SAMPLE HOLDERS FOR DETERMINATION OF CHAMFERED EDGE EFFECTS ON ATOMIC OXYGEN EROSION YIELDS

The exteriors of low Earth orbit (LEO) spacecraft are subjected to many environmental threats that can cause the surface materials to degrade. One of these threats is atomic oxygen (AO), which is formed by photodissociation of molecular oxygen by short wavelength UV radiation. Atomic oxygen exposure can result in oxidative erosion of polymers leading to structural or thermal failure of spacecraft components. The amount of AO erosion expected during a mission can be calculated by knowing the AO erosion yield (Ey, thickness loss per incident atomic oxygen atom) of the material and the AO fluence expected for the mission. The Ey can be determined through dehydrated mass loss measurements of test samples if one knows the AO fluence, density, and area of exposure. Such measurements have been made as part of flight experiments, such as the Materials International Space Station Experiment 2 (MISSE 2) Polymers Experiment. The MISSE 2 Polymers Experiment sample holders had chamfered circular apertures that controlled the exposure area, but also allowed AO to scatter from the chamfered surfaces onto the samples. This scattering increases the local flux and therefore results in an Ey which is higher than simply computing it based on the sample area. In addition, some MISSE 2 samples peeled at their edges due to this scattering effect. Sample holders with different chamfered-perimeter to exposed-area ratios have been designed for future spaceflight experiments that allow more accurate determination of the Ey for large area polymers, representative of their functional use on spacecraft surfaces.