Potential of Sensing Ultraviolet Radiation for Hypersonic Flight

Ultraviolet radiation from postshock excited-state species is a possible measurement target for flight parameter feedback sensors, but the feasibility and utility of such sensors have not yet been explored. This paper employs numerical simulations of hypersonic flowfields to estimate ultraviolet radiation generated by the bow shock of a hypothetical blunt-nosed vehicle. Multiple flowfields were generated to investigate the sensitivity of the ultraviolet radiation’s spectral features to varying freestream velocity and vehicle angle of attack. Computational solutions were reached by solving the Navier–Stokes equations coupled with a 19-species, two-temperature, finite-rate kinetic model for a two-dimensional grid around a blunt-nosed cone using NASA’s Data Parallel Line Relaxation fluid dynamic simulation suite. Discrete species and temperature compositions were extracted from the flow solutions along lines of sight originating from selected points on the body surface to calculate emission with NASA’s Nonequilibrium and Equilibrium Radiative Transport and Spectra Program, a nonequilibrium radiative transfer simulation tool. Calculated emission was integrated over a field of view and wavelength ranges corresponding to vibrational bands of nitric oxide to estimate detectable spectral irradiance at varying locations. Trends in the predicted emission were assessed in the context of sensor design for sensitivity to changes in vehicle state.