Investigation of Galileo Probe Entry Heating with Coupled Radiation and Ablation

Abstract

This paper presents a trajectory-based heating and ablation study of the Galileo probe forebody flow and thermal protection system performance. The validity of modeling assumptions regarding diffusion, radiative heating, and ablation made in previous work, including preflight predictions, are addressed. The Navier–Stokes equations are solved assuming a one-temperature chemical nonequilibrium flowfield with coupled radiation and ablation. Geometric changes in the forebody due to ablation are accounted for. Solving the Stefan–Maxwell equations to compute the species mass diffusion in the flowfield, instead of assuming a constant Schmidt number as was done in previous studies, was found to significantly increase total predicted recession by about 10% on the flank, due to increased convective heating. Application of the high-fidelity ray-tracing approach resulted in a 10% reduction in the radiative heating along the forebody when compared with the heritage tangent-slab approximation. Additional modeling approaches, such as state-specific H modeling, application of ray-tracing for coupled flowfield radiative source terms, and including precursor absorption were considered but found to have a minimal impact on recession. The resulting nominal prediction was found to be nearly within the uncertainty of the flight data along the entire surface of the probe. This improved agreement relative to past studies is due to the notable impact of shape change, multicomponent diffusion, and ray-tracing radiative heating, most of which were not included in previous models. To provide uncertainty bounds for the present simulations, an uncertainty analysis was performed. Sources of uncertainty were identified in the ablation modeling, radiation modeling, flowfield kinetics, turbulence modeling, and thermodynamic properties of select species. When the impact of all considered uncertainties are combined, the stagnation point recession varies between and of the nominal value while a near constant uncertainty band exists on the flank.