Return of OSPREE: In Situ Spectroscopic Measurements During Atmospheric Reentry

Optical emission spectroscopy measurements of the reentry shock layer can provide invaluable information aboutthe dynamic aerothermal chemistry during atmospheric reentry and yield critical data needed to improve fluiddynamics 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 duringreentry from an altitude of 105 km down through 50 km, encompassing a range of Mach numbers between 29.5 and15.0. 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 andvehicle thermal protection system. Temporal evolution of the spectral radiance of key molecules (CN, C2, CH) andatoms (O, O
, N, and H) is analyzed across the flight trajectory. Rotational and vibrational temperatures fromspectral fits are computed to provide thermometric measurements of the shock layer over time.