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April 29, 2009 -- Hoping to bridge the gap between airplanes and rocketships, the U.S. military is preparing to test an experimental aircraft that can fly more than six times faster than the speed of sound on ordinary jet fuel.

Officially, it's known as the X-51, but folks like to call it the WaveRider because it stays airborne, in part, with lift generated by the shock waves of its own flight. The design stems from the goal of the program -- to demonstrate an air-breathing, hypersonic, combustion ramjet engine, known as a scramjet.

"We built a vehicle around an engine," said Joseph Vogel, the X-51 project manager with Boeing, which is building a series of four test planes under a $246.5-million program managed by the Air Force Research Laboratory in Dayton, Ohio.

Scramjets use the forward motion of an engine to compress air for fuel combustion. It's similar to a ramjet engine, but at supersonic speeds.

NASA tested the concept in 2004, breaking the record for a jet-powered aircraft with a speed of Mach 9.6, or nearly 7,000 mph. But the vehicle, known as X-43, only flew for a few seconds and its copper-based engine was not designed to survive the flight.

"The heat from the combustion process was just absorbed by (X-43's) engine. It would hold its shape for a limited point of time and then start melting," Air Force X-51 program manager Charlie Brink told Discovery News.

The X-51 engine, made by Pratt & Whitney, is made from a standard nickel alloy and is cooled during flight by its own fuel. The program's goal is to fly for about five minutes.

"I truly believe this is one of those history leaps that will only happen every so many hundred years," Vogel said in an interview.

The military has its eye on high-speed cruise missiles as well as space vehicles that wouldn't need carry-on oxidizers. The space shuttle, for example, carries both liquid oxygen and liquid hydrogen, to power its main engines.