This thesis investigates the radiative heat transfer encountered in rarefied, hypervelocity flow conditions such as would be experienced during an aerocapture mission to Titan. Accurate estimates of the nonequilibrium radiation involved in high speed operations such as reentry are essential in order to design these thermal protection systems more efficiently. Because the mass of the thermal protection system is a large fraction of the overall vehicle mass, there is great interest in designing lighter and more efficient systems. Flight experiments are expensive and restrictive, hence laboratory testing is needed in facilities that are capable of producing hypervelocity flow. Unfortunately, as the size of a typical flight vehicle is too large to reasonably test in experimental facilities, subscale models of the aeroshell vehicles are generally tested. The University of Queensland's expansion tube facilities - X1, X2 and X3 - have been widely used for subscale modelling of hypersonic flowfields (Morgan 2001). Ground testing facilities such as the X2 facility take advantage of binary scaling to test small scale models of flight vehicles, which is the most important parameter to match in order to reproduce high speed flight. Binary scaling, also called 'ƒÏL' scaling, requires that the multiplication of density and the characteristic length of the vehicle be balanced between flight and experimental conditions. However, it was shown by Capra (2007) that radiative heat transfer does not follow this same scaling factor, and true similarity with flight is not created for flows where the radiative and convective heat transfer are strongly coupled. This can result in significant errors in the estimates of the associated flow properties and the estimation of the heat transfer due to radiation. The X2 facility was modified in 2006 to allow experimentation at low pressures in nonreflected shock tube mode. Nonreflected shock tube operation allowed the taking of true-flight density measurements of the radiative heat transfer and removed the scaling problems involved in radiation measurements for model vehicles, at least for part of the flowfield. Measurements were made in the region immediately behind the shock along the centreline of the core flow, where the shock remained planar. External flow fields, such as those surrounding a reentry capsule, were not reproduced. The low density operating limit was approximately 10 Pa, limited by boundary layer growth on the walls.
