The objective of our work is to develop improved thermal response models of the AVCOAT thermal protection system (TPS) from first principles, and to validate the results of these models with measured in-depth temperature and calorimeter data from EFT-1 data. True high-fidelity porous TPS modeling is notoriously difficult because the decomposition of the porous TPS media involves complex multi-component and chemically reacting gas flow and the heterogeneous thermochemical reactions cause gradual recession of both the fibers and resin which make up the TPS material. To achieve a fundamental understanding we will employ molecular dynamics simulations to characterize the ablation chemistry and rate of void formation. New grid-free DSMC simulations will be used to model gas transport, heat transfer, and TPS material regression at the mesoscale level. Finally, the macroscopic material properties derived from DSMC will be used in a one-dimensional macroscopic heat transfer model to enable direct comparison with the EFT-1 data.