Reduced atomic collisional-radiative model for VUV radiation prediction in Earth's reentry

During hypervelocity reentry into Earth's atmosphere, a significant part of the radiative heat flux experienced by the spacecraft is emitted in the Vacuum Ultraviolet (VUV), in the nonequilibrium part of the post-shock region. Using radiation measurements for typical Moon or Mars return conditions performed at NASA Ames in the Electric Arc Shock Tube (EAST) facility, the main atomic electronic states responsible for the intense radiation in this wavelength range have been identified as being the fourth and fifth electronic states of atomic nitrogen and the fifth electronic state of atomic oxygen. We have developed a collisional-radiative (CR) model to predict the population of these emitting states and compared the predictions given by other CR models used in the aerospace community. The most significant mechanisms driving the evolution of these electronic states have been identified, leading to a reduced CR model to a set of seven electronic states and twenty-eight reactions.