Beyond the security fence, a modified engine from a Cold War-era fighter jet is used to replicate the very high temperature airflow generated at hypersonic speeds. The superheated air is blasted through a light-weight, ring-like device made up of thousands of thin-walled tubes through which coolant is passed. The aim of this precooler is to remove the extreme heat very quickly. When used in the  Sabre engine, it"s hoped it will prevent its internal components melting in the high temperatures and ensure the engine runs efficiently.