Modeling Material Behavior in Space and Other Extreme Environments

Understanding material performance is crucial to spacecraft design. However, the impact of the space environment, particularly with respect to photoemission, is not well understood. We will present research on the coupling of material properties and orbital environments to determine how material properties such as the work function are modified and explain how those characteristics may contribute to the increased photoemission and surface charging behaviors observed in orbit. Spacecraft charging is dependent on the properties of spacecraft materials. Description of spacecraft charging requires knowledge of the photoemission and secondary emission yields (i.e. how many electrons are emitted per incident photon, electron, or ion) as well as other material transport properties such as conductivity, relative dielectric permittivity, and electric field thresholds for electrostatic discharge . Charging models commonly assume that the material properties are static, typically obtained from databases compiled with terrestrial laboratory experiments where spacecraft materials are analyzed in clean (e.g., beginning-of-life) conditions. However, it is well known that as soon as the spacecraft begins to interact with the space environment, its material properties begin to change and continue to evolve during the mission. In addition to the plasma particles described above, the other harsh elements of the space environment (atomic oxygen (AO), in particular for low-Earth orbit, and bio-hazardous [4, 5] and material-degrading radiation) can alter the properties of spacecraft materials via surface chemistry effects (oxidation, contamination), erosion, and defect creation (bond breaking, trap creation, irradiation etc.). In this work we explore how material properties and orbital environments can modify the materials work function and explain the increased photoemission observed in orbit by combining first principles studies of material properties, molecular dynamics modeling of AO and UV damage to exposed materials, and plasma flux modeling of orbital environments.