Atomic oxygen in low Earth orbit (LEO) readily attacks and oxidizes exposed spacecraft polymeric materials such as polyimide Kapton photovoltaic array blankets. The application of thin film silicon dioxide protective coatings can greatly extend the useful life of such materials in LEO. A Monte Carlo computational model has been developed which simulates atomic oxygen interaction with polymeric and protective coating materials for both ground laboratory and in-space experiments, allowing the determination of the geometrical shape of atomic oxygen attack of protected polymeric materials at defect sites in protective coatings. Modeling of attack of unprotected carbon-carbon composite materials predicts textured surfaces suitable for high emittance radiators. Results for fiberglass composites indicate loss of the matrix polymer leading to friable fibers. The computational modeling to project in-space performance based on ground laboratory testing predicts mass loss per fluence in space to be approximately one third that observed in plasma ashers.