Influence of Non-Boltzmann Radiation around Titan Atmospheric Entry Vehicles

This work aims to improve the predictive accuracy of non-Boltzmann radiation in Titan atmospheric entry. Nominal thermochemical nonequilibrium and radiation models are devised on the quasi-one-dimensional flow field solvers that allow computationally efficient and detailed physical investigations. Along the stagnation line, not only the CN Violet and Red bands in ultraviolet, but also vacuum ultraviolet emission from nitrogen species significantly contributes to the radiative heating. Sensitivity analysis unveils the important ranks of relevant reaction mechanisms contributing to the CN composition and intensity profiles. Selected three parameters, which are the N₂ +N₂ dissociation, and collisional excitation and dissociation rates of CN+N₂, are calibrated via Bayesian inference against the shock tube measurement from NASA Ames Research Center. Although the calibrated parameters successively reproduce the measured intensity profile, the determined N₂ +N₂ dissociation rate has large discrepancy compared to widely adopted values by factor of 83. So called mixture effect is then investigated by comparing macroscopic QSS rates between pure nitrogen and Titan composition. As a result, the mixture effect has negligible impact, and rationale of the large dissociation rate obtained from the present calibration needs to keep investigated.