Traveling 29,000 meters above Earth, a small unmanned craft last week became the first airplane to fly powered by an exotic type of engine known as a scramjet. The wedge-shaped vehicle, called an X-43A or Hyper-X, separated from its booster rocket and zoomed at a hypersonic speed of seven times the speed of sound—a record for air-breathing jet planes.
Although the little plane’s self-powered flight lasted only 11 seconds, that brief journey on March 27 marks a major milestone on the way to a new breed of very fast airplanes, comments Werner J.A. Dahm of the University of Michigan in Ann Arbor. Such hypersonic jets could potentially ferry payloads cheaply to the brink of space or deliver lethal force anywhere around the globe in just a couple of hours (SN: 9/19/98, p. 182: http://www.sciencenews.org/pages/sn_arc98/9_19_98/fob5.htm). Eventually, hypersonic transports carrying passengers may zip just as quickly over the Pacific, Dahm adds.
Speeds greater than five times the speed of sound are called hypersonic. This minimal hypersonic speed, or Mach 5, is 1.7 kilometers per second. Scramjets work properly only when traveling above Mach 5.
The 3.7-meter-long X-43A that flew last week was the second of three nearly identical prototypes built for NASA by a private company. In 2001, when NASA first tried to fly one of the aircraft, the mission failed because the booster rocket went out of control.
Although bullet-shaped scramjet-powered projectiles have flown successfully before (SN: 9/22/01, p. 191: Available to subscribers at Futuristic engine proves its mettle), the latest flight was “a significant step forward” because the engine was part of a vehicle with structures for lift and control like those of an ordinary plane, says program manager Vincent L. Rausch of NASA Langley Research Center in Hampton, Va.
In development since the 1960s, the scramjet employs sophisticated aerodynamic features so it can take oxygen for combustion from fast-flowing air while preventing that fierce wind from blowing out the engine’s flame. Unlike a rocket, the aircraft doesn’t need to carry oxygen-rich substances to combine with its fuel, Rausch notes.
Given that attraction, NASA isn’t the only agency pursuing the technology. At the end of summer, the Defense Advanced Research Projects Agency (DARPA) is scheduled to attempt a 30-second, Mach 6 flight by a half-size prototype of the missile dubbed HyFly, says Preston H. Carter, who manages several DARPA hypersonic-vehicle programs.
Meanwhile, NASA researchers say they are planning to fly the last X-43A for about 11 seconds at Mach 10 by next fall.