Investigating the Interactions Between Radiation and Ablation During Earth Entry Using a Loosely-Coupled Framework

High-speed entry vehicles are subjected to harsh environments when entering the atmosphere. The high temperatures in this regime can lead to electronic excitation and ionization, producing large amounts of electromagnetic radiation as electrons transition between energy states. Furthermore, the high-temperature gas may chemically react with thermal protection system material, causing ablation and pyrolysis products to be injected into the near-wall region. Not only are both of these phenomena challenging to model in isolation, but they also may interact with each other. These interactions necessitate using a coupled simulation framework to adequately model the planetary entry environment. Such a framework is developed in this paper by joining together flow, radiation, and material response solvers. The coupled codes are used to study the impact of radiation and material response on the Stardust capsule during Earth entry. Using the framework, it is seen that ablation creates a notable decrease in the heat flux at the vehicle surface, while radiation has a much smaller effect. Furthermore, under the assumptions and limitations of the current study, the ablation products are shown to have minimal impact on the radiative character of the boundary layer, as the near-wall gas is still dominated by nitrogen and oxygen, with very little contribution to emission or absorption by carbon species.