Spacecraft charging and subsequent vacuum arcing poses a significant threat to satellites in LEO and GEO plasma conditions. Localized arc discharges can cause a flashover plasma expansion, that can lead to further discharge of charge stored on dielectric surfaces such as solar panel arrays, which can cause catastrophic events over large areas of the panel array surfaces. While spacecraft charging has been studied for a long time, the dynamics of flashover currents and propagation of the expanding plasma have not be well-characterized, although they are key in order to understand how to mitigate damage to solar panel arrays during discharge events. This project will improve the understanding of arc discharges and expanding plasma effects on dielectric structures such as solar panel arrays so that NASA will better be able to protect satellites from damaging vacuum arc discharges. We will develop accurate numerical simulations that model localized arcs, plasma expansion, and dielectric charging and discharging, under both simulated LEO and GEO plasma conditions. We also plan to extend our models to include the effects of non-uniform ambient plasma densities, secondary electron emission effects, and photo-electron effects. In Phase I, we will validate our numerical models against the theoretically known problem of expansion of a plasma into a vacuum, and will develop detailed simulations of a new AFRL round-robin experiment to test plasma propagation speeds in the presence of a charged dielectric material. We also plan to develop easy-to-use GUI interfaces so that NASA scientists will be able to use high-performance computing resources to examine the parameter space for these types of problems without having to dive deep into the code infrastructure and numerics of the simulations. At the conclusion of Phase II we plan to provide NASA and AFRL scientists with tools that they can use to better understand discharges on satellites and mitigate damage to solar arrays.