Shock tube experiments are a primary means of obtaining ground test data for the hypersonic regime. Accurate characterisation of the test gas is crucial to understanding experimental results. However, characterisation of the flows produced behind the shockwave has historically proven challenging. This paper applies a methodology to calculate the shocked test gas properties using the experimentally recovered shock speed profile. Static pressure, Pitot pressure and heat transfer predictions are found to closely match the experimental data for a range of shock trajectories with both Argon and Air test gases. Thermochemical variations in the test gases are found to depend strongly upon variations in shock speed along the tube, and it is shown that characterisation of the test gases requires accommodating the influence of wave effects associated with the varying shock speed. Tube diameter is found to influence test time significantly, and also the magnitude of nonuniformities in the test gas. Location and number of shock timing stations in experimental facilities are found to play a vital role in the ability to accurately characterise the test gas of a given experiment.

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The Ice Giants, Uranus and Neptune, represent a largely unexplored, interstitial class of planetary objects that fit between the Gas Giants and the smaller terrestrial worlds, such as Earth, in terms of their size and elemental composition and are therefore a missing link in our understanding of extrasolar planetary evolution. The scientific potential of a mission to the Ice Giants is well recognised and has been identified by NASA and ESA as a high priority on several occasions, most recently in the 2023 -2032 Decadal Survey. The payload capacity of such a spacecraft is limited by the requirement for a bulky heat shield, made necessary by the paucity of ground test data for convective and radiative heat flux at proposed entry trajectories. This paper describes an experimental study of shock layer radiation via emission spectroscopy at Ice Giant entry conditions in the T6 free-piston driven wind tunnel. Shock waves of up to 18.9 km s −1 were driven through H/He mixtures containing up to 5% CH 4 by mole. The magnitude of spectral radiance at the peak and in the immediate post-shock region appears to be strongly affected by the concentration of CH 4 in the test gas. Thorough cleaning of the shock tube between each test was found to be very important for obtaining high quality data given the relatively low signal levels.