A capsule entering a planetary atmosphere at hypersonic speeds experiences high levels of radiative heating. Furthermore, coupling between the ablation products from the surface of the vehicle and the high temperature gas can have a major effect on the head load experienced by the vehicle. This paper discusses a collaborative project aimed at better characterising the flow processes involved. A ground-based expansion tube facility is described in which radiation-ablation coupling is achieved through the use of a pre-heated model placed in a high temperature flow. In parallel, simulation techniques are being developed to model the complex chemical processes occurring in the flow.