Radiative Emission Model Comparisons Against In Situ Emission Data of the Varda’s Reentry Capsule

Nonequilibrium aerothermodynamic modeling of the Varda hypersonic testbed capsule is conducted with direct simulation Monte Carlo (DSMC) and computational fluid dynamics (CFD) solvers. Flowfield properties at the 78 km reentry trajectory point are extracted to compute line-of-sight spectral radiance using two radiative emission codes, namely, High-Temperature Aerothermodynamic Radiation Algorithm (HARA) and Nonequilibrium Air Radiation (NEQAIR). Computed spectra are compared to spectral radiance measured by an in situ optical emission spectroscopy payload flown on Varda’s W-2 capsule in 2025. Model comparisons to the experimental data reveal discrepancies between the HARA and NEQAIR radiative emission predictions in both overall magnitude and qualitative behavior. NEQAIR was found to underpredict spectral radiance by up to two orders of magnitude compared to HARA above 500 nm. These discrepancies are described and identified as resulting from the non-Boltzmann [Formula: see text] emission band model.