In Cologne, the researchers have access to a wind tunnel heated by an electric arc system, in which models can be exposed to realistic thermal loads. Optical and electronic metrology systems are used to examine the flow characteristics of the hot gases and the local thermal loads being experienced by individual sections of the model. Space capsules enter the atmosphere with their unstreamlined undersides facing in the direction of travel. This gives rise to a shock wave at high temperatures, while the gases flowing past the sides of the capsule are significantly cooler as they pass the other end of the capsule.