Validation of CO 4th positive radiation for Mars entry

This paper presents measurements and simulations of CO 4th Positive equilibrium radiation obtained in the NASA Ames Research Center's Electric Arc Shock Tube (EAST) facility. The experiments were aimed at measuring the level of radiation encountered during conditions relevant to high-speed entry into a simulated Martian atmosphere (96% CO2: 4% N2). The facility was configured to target several ranges of nominal Mars entry conditions, of which 7.35 km/s at 0.1 Torr (13.3 Pa), 6.2-8 km/s at 0.25 Torr (33 Pa) and 7.1-7.8 km/s at 1 Torr (133 Pa) are examined in this paper. The CO 4th Positive system was chosen to be the focus of this study as it accounts for a large percentage of the emitted radiation for Martian entry, and also due to the difficulties of obtaining experimental validation data due to the emission appearing in the Vacuum Ultra Violet (VUV) spectral range. The focus of this paper is to provide a comprehensive comparison between the EAST data and various CO 4th Positive databases available in the literature. The analysis endeavors to provide a better understanding of the uncertainty in the measurements and quantifies the level of agreement found between simulations and experimental data. The results of the analysis show that the magnitude of the CO 4th Positive radiative intensity is very sensitive to the flow temperature. Subsequently, simulations using thermodynamic equilibrium generally under-predict the experimental data by approximately a factor of up to 2. However, when simulations are performed using a flow temperature extracted from the black body limited portion of the CO 4th Positive spectra taken from experiment, the agreement between the EAST data and simulations is generally very good. Furthermore, comparisons of experimental data and simulations across other spectral regions provide additional support for the use of the black body temperature.

► Measurements and simulations of CO 4th Positive radiation are presented. ► Validation of spectroscopic database with experimental shock tube results. ► Equilibrium simulations significantly under-predict CO 4th Positive. ► Simulations using a black body temperature extracted from experiment produce much better agreement.