Modeling of sodium radiation from reentry flows at high altitudes

A kinetic-based quasi-steady-state model is developed to study sodium radiation intensity for reentry high-altitude flows of the blunt-body Stardust and a slender body. The sodium detected in the high-speed Stardust-reentry flow was from an impurity of the ablative thermal protection material. In this work, the particle-based direct simulation Monte Carlo method is used to obtain flow solutions, and a quasi-steady-state model is used to derive the sodium number-density distributions in the ground and excited electronic states. The sodium radiation intensity is calculated based on the sodium number-density distributions in the excited states and agrees reasonably well with the observation data for the Stardust reentry at 81 km. It was also found that sodium radiation in the slender-body reentry flow will be orders of magnitude less than the value observed for the blunt body.