Extension of Multiband Opacity-Binning to Molecular, Non-Boltzmann Shock Layer Radiation

Abstract

For accurate predictions of shock layer radiative heating to reentry vehicles, the smeared rotational band (SRB) model is appropriate for molecular band systems with negligible self absorption, meaning they are optically-thin. However, for band systems with noticeable self absorption, the orders-of-magnitude more computationally expensive line-by-line (LBL) approach is required. Considering past and proposed NASA missions, the molecular band systems most likely to require the LBL approach are the CO 4th-Positive, CN Violet, and CO2 IR bands. The CO 4th- Positive and CN Violet bands are required for Mars entry at velocities greater than 6 km/s, with the CN Violet band also required for Titan entry. These two bands typically emit strongly in flow regimes with non-Boltzmann upper electronic state populations. The CO2 IR band is required for Mars entry at velocities below 5 km/s. This ro-vibrational band system is typically assumed to contain Boltzmann populations of radiating levels (the quality of this assumption is the subject of other studies)