Investigation into the Differences Between Atomic Oxygen Erosion Yields of Materials in Ground-Based Facilities and LEO

The atomic oxygen erosion yields of various materials, measured in terms of volume of material oxidized per incident oxygen atom, are sometimes very different for materials exposed in ground-based atomic oxygen facilities compared to those exposed in low Earth orbit (LEO) for the same materials. This difference has often been attributed to a synergistic reaction between atomic oxygen and vacuum ultraviolet radiation present in many ground-based atomic oxygen facilities. Energy and presence of charged species has also been thought to play a role in this observed difference in erosion yield. Using an isotropic thermal energy atomic oxygen source and a hyperthermal atomic oxygen directed beam, an attempt was made to isolate each of these factors for polyimide Kapton HN, polyethylene, and FEP Teflon to determine the sensitivity of the erosion yield to each factor. It was found that each polymer appears to have atomic oxygen synergistic effects with different components of the environment. Isolating each environmental component to determine the important component for a particular material is an important step in enabling better durability prediction using ground-based facilities. Ground testing using the expected space environment components and the development of correlation factors to better relate the ground test to a particular mission environment are important to project in-space material durability.