Radiation measurements in rarefied Titan atmospheres

For reentry operations into atmospheres such as Titan, accurate, reliable radiation data is essential for estimating the total heat transfer experienced by the vehicle. Experiments are being undertaken in the X2 facility at the University of Queensland to measure the radiation produced by superorbital entry in the rarefied section of the trajectory. These experiments use the Nonreflected Shock Tube (NRST) mode of experimentation, which allows full-scale measurement of the radiation in the flow. This paper presents results from the continuing experimental work being conducted in the X2 facility, focussing on freestream pressures between 2 and 13 Pa for a 98% N2, 2% CH4 Titan gas mixture. For radiating flows with Titan gas, the main radiator of interest is CN (cyanogen), formed in high concentrations in the nonequilibrium region behind the shock. The experimental data includes static and pitot pressure measurements of the flows and a spectrometer is used to capture the radiation in the CN violet band. Flow visualisation is also achieved with a high speed camera.