Equilibrium Radiative Heating from 9.5 to 15.5km/s for Earth Atmospheric Entry

This paper presents an overview of the analysis and measurements of equilibrium radiation obtained in NASA Ames Research Center's Electric Arc Shock Tube facility as a part of recent testing aimed at reaching shock velocities up to 15.5km/s. The goal of these experiments was to measure the level of radiation encountered during high-speed Earth entry conditions, such as would be relevant for an asteroid, interplanetary, or lunar return mission. These experiments provided the first spectrally and spatially resolved data for high-speed Earth entry and cover conditions ranging from 9.5 to 15.5km/s at 13.3 and 26.6Pa (0.1 and 0.2torr). The present analysis endeavors to provide a detailed comparison of shock tube radiation measurements and simulations at high-speed conditions. A comprehensive comparison between the spectrally resolved absolute equilibrium radiance measured in the Electric Arc Shock Tube facility and NASA's predictive tools is presented. To provide a more accurate representation of the agreement between the experimental and simulation results, the integrated value of radiance is compared across four spectral regions (vacuum ultraviolet, ultraviolet/ visible, visible/ near infrared, and infrared) as a function of velocity. Results have generally shown excellent agreement between the two codes and the shock tube data for the ultraviolet through infrared spectral regions; however, discrepancies have been identified in the vacuum ultraviolet. As a result of the analysis presented in this paper, an updated parametric uncertainty for high-speed radiation in air is evaluated to be [9.0%, -6.3%]. Furthermore, due to the nature of the radiating environment at these high shock speeds, initial calculations aimed at modeling phenomena that become more significant with increasing shock speed are performed. These phenomena include analyzing the radiating species emitting ahead of the shock and the increased significance of radiative cooling mechanisms.