Experimental study of Saturn entry radiation with higher amount of diluent in an expansion tube

The aerodynamics of entry into gas giants are dominated by thermochemical processes occurring in the shock layers. These processes are specific to the gas giants, with their unique atmospheric composition of hydrogen and helium, and are not well understood. This paper used the condition with the maximum enthalpy which can be achieved in the expansion tube, X2, as well as increased helium content in the test gas, to generate a radiation field representative of blunt body Saturn entry. These are the first spectrally resolved radiation measurement ever performed in an impulse facility to study simulated Saturn entry. Both high speed imaging and spectrometry were employed to measure the atomic hydrogen radiation emitted from Balmer series of hydrogen atoms. The bright region in the radiation field merely exists near the model surface, indicative of the slow ionization process,which causes the electron number densities to build up only near the surface. From the central streamline spectral data, H-α was the strongest transition, while other transitions (n < 3) were negligible after the shock, and became brighter near the body. Both the horizontal radiance profile and high speed image were employed to locate the focused slices in vertical shots. It was also found by the Specair calculation that self-absorption is more likely to occur in H-α radiance than in H-β radiance with the line of sight in this study.