Return of OSPREE: In Situ Spectroscopic Measurements During Atmospheric Reentry

Optical emission spectroscopy measurements of the reentry shock layer can provide invaluable information about the dynamic aerothermal chemistry during atmospheric reentry and yield critical data needed to improve fluid dynamics modeling of reentry systems. On 28 February 2025, the U.S. Air Force Research Laboratory successfully executed the Optical Sensing of Plasmas in the ReEntry Environment (OSPREE) experiment using Varda Space Industries’ W-2 hypersonic test-bed vehicle, obtaining in situ shock-layer radiative emission measurements during reentry from an altitude of 105 km down through 50 km, encompassing a range of Mach numbers between 29.5 and 15.0. We present a summary of the reconstructed trajectory and the optical emission spectra obtained during flight, noting key emissions pointing to evolving shock-layer thermochemistry and interactions between the flowfield and vehicle thermal protection system. Temporal evolution of the spectral radiance of key molecules (CN, [Formula: see text], CH) and atoms (O, [Formula: see text], N, and H) is analyzed across the flight trajectory. Rotational and vibrational temperatures from spectral fits are computed to provide thermometric measurements of the shock layer over time.