Comparing Aerothermodynamic Models With Emission Spectroscopy Data From the Atmospheric Reentry of the W-2 Hypersonic Testbed Vehicle

In situ Visible - Near Infrared (Vis-NIR) optical emission spectroscopy (OES) measurements obtained during the atmospheric reentry of Varda Space Industries’ W-2 capsule are compared with aerothermodynamic model predictions of shock layer spectral radiance computed by state-of-the-art fluid dynamics and radiative solver codes. Comparisons between flight data and computed spectra are conducted across 340 - 800 nm and focus on molecular emissions of N2, N2+, and NO as well as the atomic oxygen peak at 777 nm. The SPARTA direct simulation Monte Carlo (DSMC), LAURA computational fluid dynamics (CFD), and HARA radiative solver codes are used to simulate the flowfield from 85 km to 55 km, encompassing a Mach range between 28.0 and 20.0. LAURA-driven computations overpredict radiance above 65 km by up to a factor of 2, while SPARTA-driven computations shown excellent agreement with flight data between 85 km and 75 km. O 777 nm radiance is significantly underpredicted across the trajectory due to breakdown of quasi-steady state (QSS) assumption conditions and local continuum breakdown along the line of sight above 70 km. Detailed analysis of aerothermodynamic parameters at 78 km indicate that overprediction of spectral radiance by LAURA-HARA is driven by high computed electron number densities as well as challenges in using a single continuum or kinetic based method to capture reentry shock-layer thermochemistry in transition flow conditions.