Spectrally Filtered Imaging and Vacuum Ultraviolet Spectroscopy of Preheated Models in X2

This study presents calibrated vacuum ultraviolet spectroscopic measurements and filtered cyanogen violet band images for steel, cold graphite, and preheated graphite models at three reentry-relevant conditions in the X2 Expansion Tube. An analysis of these experiments concluded that there were no unique radiating species in the boundary layer of an ablating model within the spectral range of 120-180nm. Spectral measurements showed an increase in atomic carbon emission in the boundary layer with preheated graphite models. Filtered images revealed significant cyanogen emission in the boundary layer of the preheated graphite models. A comparison with spectral measurements concluded that the production of cyanogen in the boundary layer did not reduce the nitrogen line emission relative to the shock layer. The increase in the cyanogen boundary-layer emission relative to the shock-layer emission was found to vary with freestream conditions.