Sensitivity of External Emission Spectroscopy for Hypersonic Vehicle Control

At hypersonic velocities, shock-excited air near the external surface of the vehicle includes light-emitting electronically excited species that can be observed using optical emission spec- troscopy (OES). The current work is motivated by design of an externally oriented OES sensor that can be used for hypersonic vehicle control. An investigation into trends in nitric oxide (NO) emission from potential sensor configurations and flight parameters is conducted. To estimate the emissive species present in the post-shock region, gas composition and thermochemical states were calculated using two methods. Emission spectra were calculated using NASA’s NEQAIR Non-equilibrium Radiative Transport and Spectra Program, and simulated emission from the two flow models are compared. The simulated spectra’s sensitivity to a vehicle’s flight velocity, body geometry, and OES sensor configuration are qualitatively evaluated to assess trends that may inform design and mission constraints for a novel hypersonic application OES sensor. Preliminary work towards designing a sensor is accomplished by comparing experimentally measured emission from a shock tube with simulated emission generated from NEQAIR and a finite rate chemical kinetic model.