NASA scientists celebrated the dawn of a new era in powered flight when, on the morning of 27 March, the X-43A jetlet go an 11-second burst of exhaust that propelled the plane to a speed greater than Mach 7, or seven times the speed of sound. The test flight began with a B-52B bomber carrying aloft the X-43A attached to a Pegasus booster rocket. The X-43A's 11-second flight at 28 950 meters was the first successful demonstration of scramjet technology, which eventually will propel an aircraft into suborbital flight above the atmosphere at speeds approaching Mach 10 [see " Hypersonic Flight," IEEE Spectrum, January].
A scramjet--short for supersonic combustion ramjet--engine draws oxygen for combustion of its fuel supply directly from the air, and so, unlike rockets, it doesn't have to carry an onboard oxygen supply. This yields a tremendous weight savings. Because the air taken in from the atmosphere enters the engine's vent with tremendous force, there is no need for the rotating blades that compress the air in a conventional jet engine before combustion occurs.
The public face of the scramjet enterprise has been the wistful daydream of a future where a flight from New York City to London takes less time than a subway ride from Manhattan to Brooklyn. But scramjet engines will likely find their first use as the boosters of choice for a range of military applications. Paul Beaver, a defense analyst with Ashbourne Beaver Associates Ltd. in London, told the Financial Times that "the X-43 has everything to do with defense and very little to do with civil aerospace."
Beaver points out that DARPA, the Pentagon's Defense Advanced Research Projects Agency in Arlington, Va., has revived plans for a so-called hypersonic cruise vehicle in the guise of Project Falcon. That project was set up to foster the development of a reusable aircraft that can strike a target anywhere in the world within two hours after taking off from the continental United States.