Future probes to Neptune and Uranus will experience extreme heating rates due to the high speed of entry. For the Galileo missions, the heat flux was dominated by the radiative component from the gas to the surface and was higher than that experienced in a thermonuclear explosion. To ensure the survival of the spacecraft, a significant proportion of the total mass budget is used for the Thermal Protection System (TPS). Uncertainty in radiative heating rates leads to increased TPS margins, ultimately leading to a reduction in scientific payload. At high speeds, a non-equilibrium thermochemical region exists in the shock layer, as the time for gas particles to traverse a significant distance is less than the time for the gas reach a state of equilibrium. The non-equilibrium gas is a large contributor to the overall radiative heat flux. As the shocked gas expands around the back of the vehicle, the rapid change in flow conditions leads to a secondary region non-equilibrium thermochemistry. Our knowledge of these non-equilibrium processes are based on compressing shock tube experiments. However, there is limited knowledge about these rates in an expanding flow scenario. This proposal aims to address this by developing a novel experimental methodology by studying the unsteady expansion of a characterised shock heated gas. This overcomes some of the challenges of scaling of radiative processes for sub-scale models and large uncertainties in freestream gas properties. This will provide a unique reference validation dataset for the outer Gas Giants for use in the broader research community. Testing will be performed in the Oxford T6 Staler tunnel, which has been established to perform emission radiation experiments as a shock tube. The in-house shock tube simulation code FROSST will be applied to model the unsteady expansion process. Close collaboration with Fluid Gravity Engineering will be maintained to select conditions of interest to any possible missions.
