Current turbojet engines cannot propel an aircraft to hypersonic speeds -their spinning shafts and compressors would simply collapse. To solve this problem, groups in the United States, Japan, Australia, and other countries are working on a propulsion system that burns fuel combined with air flowing at supersonic speeds through the engine, which is essentially a metallic funnel, with no moving parts. These so-called supersonic combustion ramjet (scramjet) engines, outlined in this article, could in theory propel an aircraft to Mach 10 and eventually even more.