Scramjet

A scramjet, short for supersonic combustion ramjet, is a jet engine with no moving parts that burns fuel in air still traveling faster than sound as it passes through the engine, unlike a conventional ramjet, which slows incoming air to subsonic speed before combustion begins. Because the engine relies entirely on the vehicle's own extreme speed to compress incoming air, a scramjet only functions above roughly Mach 5, where turbine engines and ordinary ramjets can no longer operate. The concept grew out of American aerospaceplane research of the 1950s and 1960s associated with researchers including Alexander Kartveli and Antonio Ferri, and reached a major milestone in 1991 when a joint Soviet and NASA hydrogen-fueled scramjet, launched aboard a modified surface-to-air missile, flew at Mach 5.5 in the first successful scramjet flight test.