Space vehicles traveling at hypersonic speeds through a planetary atmosphere experience heat loads greater than 50 W cm -2 and require a heat shield to protect the vehicle from severe heating . A class of materials used for several space missions comprises carbon-phenolic composites, where a network of carbon fibers is infused with a phenolic resin. Heat shields undergo a process called ablation (loss of material) under these extreme conditions. Ablation can occur through pyrolysis, gas-surface oxidation, and sublimation. Pyrolysis is the thermal decomposition of the phenolic resin, which occurs in the range of 200-1000 °C, where gaseous thermal decomposition products are expelled from the heat shield material . Pyrolysis exposes the underlying carbon fiber network, which is a porous network of sp 2 carbon. Temperatures on the outer face of a heat shield can exceed 2000 °C under hypersonic entry conditions and oxygencontaining atmospheric gases (e.g., O2, CO2) may dissociate to oxygen atoms in the boundary layer, leading to aggressive oxidation of carbonaceous material. Ablative heat shields are currently overdesigned as a result of large uncertainties in the understanding of the oxidation mechanisms . A better understanding of the oxidation process would enable improved carbon-oxygen kinetic rate models for computational fluid dynamics (CFD) and direct simulation Monte Carlo (DSMC) simulations of heat shield behavior during hypersonic flight .