NASA KY EPSCoR RIDG-25-012: Measurements of Vibrational Nonequilibrium in High-Enthalpy Flows

Abstract: Thermal protection systems are used to shield critical parts of spacecraft from the extreme thermal loads during atmospheric reentry. The total transfer of thermal energy to the heat shield materials is determined by a combination of radiative and convective heat flux. Predicting both of these components correctly requires accurate knowledge of the thermal state of the hot gas surrounding the spacecraft, whereby nonequilibrium states can significantly deviate from equilibrium calculations. Especially in the boundary layer and in the wake region of blunt re-entry bodies, the shocked and subsequently expanded approach flow can experience significant nonequilibrium, making accurate predictions in these regions more challenging. Experimental measurements of such nonequilibrium population distributions are crucial for the advancement and validation of predictive computational capabilities for thermal protection systems, e.g. within the framework of the NASA Entry Systems Modeling (ESM) project. To this end, the proposed research will develop capabilities for the quantitative measurement of rotational and vibrational state distributions in diatomic molecules near a sample surface exposed to a high-enthalpy plasma stream, as well as the determination of the sample surface temperature and total heat flux.