There is, justifiably, a great interest currently in the study and development of scramjet engines for hypersonic flight applications. A major impetus is the potential to reduce space accessibility costs by use of vehicles that use air-breathing propulsion from takeoff to the edges of the atmosphere; defense applications for hypersonic flight within the atmosphere are also of considerable interest. In the hypersonic flight regime, commonly considered to begin when velocities exceed Mach 6, the scramjet engine's specific thrust surpasses that of any other propulsion system. Subsonic combustion, which technologically is easier to manage with the current knowledge, would be associated, in the hypersonic regime, with high stagnation temperatures that would lead to unacceptable dissociation levels, and hence an inability to materialize the energy rise expected through chemical reactions. Additional thermal and structural considerations preclude the use of other air-breathing propulsion systems at these flight velocities.

In the late 1950s, when scramjet research began, the development of this type of engine proceeded with varying degrees of intensity, as the national interests of the times drove investment levels. The past decade has seen increased enthusiasm in all sectors because of the expansion of government-funded scramjet research and numerous national and international collaborations, and development has been buoyed by significant scientific and technological progress. Major activities at the national level and international collaborations exist in Europe, including Russia, and in Japan, Australia, and the United States.