Evaluation of the Radiance of Shock-Heated Air in the 120–400-nm Spectral Range

Abstract

The need to evaluate the radiative heat flux to a descending spacecraft motivated a series of ongoing studies aimed at measuring radiation fluxes behind the shock-wave front over a wide range of wavelengths at low initial pressures and high flow velocities. In the present chapter, the experimental results are presented for the emission intensity of shock-heated air behind the front of an incident shock wave at an initial pressure of 0.25 Torr and shock-wave velocities from 6.3 up to 8.4 km/s. The radiation intensity was measured in absolute units in the form of spectral distribution over a wavelength range of 120−400 nm. It was shown that the radiation flux is significantly higher at the wavelength 120 nm than the radiation flux from the same source within the wavelength range of 200−400 nm. Our experimental results demonstrated that the duration of the radiation of shock-heated air was about 1μs for all shock-wave velocities over the entire spectral range at pressure upstream of shock-wave front of 0.25 Torr. The intensities of the radiation of the N and O atomic lines at 120, 130, 141, and 149 nm were found to be much higher than the intensity of the background radiation.