UPDATE: Today’s X-51 hypersonic missile test was scrubbed. “A tanker ship sailed into the splash zone,” our spy says. “Next attempt tomorrow.”

By the end of Tuesday, the Air Force could be a whole lot closer to a hypersonic cruise missile — a Mach 6 weapon that’s 10 times faster than the old-school type.

After some technical issues forced a testing delay, the Air Force’s X-51 WaveRider will make its first flight attempt Tuesday. And if all goes to plan, it will be the longest-ever hypersonic flight powered by scramjet propulsion — little more than air and plain ol’ jet fuel.

The X-51 flight is all part of an effort to develop a new class of cruise missile that can handle hypersonic flight, a concept that overlaps neatly with the Pentagon’s interest in what it calls “prompt global strike” — the ability to reach out and blast a target over long distances, on extremely short notice.

But it’s also technically challenging. Sustained hypersonic flight is considered to be real stretch for an air-breathing vehicle — this excellent primer by Noah Shachtman explains why — but the WaveRider’s unique shape employs the shockwaves created by hypersonic flight to create lift, as well as compress the air from the atmosphere to mix and burn with its fuel.

The test will be run from Edwards Air Force Base, California. As this conceptual video shows, a B-52 will carry the WaveRider aloft. Once it reaches 50,000 feet, the B-52 will release its payload. The solid rocket booster will then kick in, taking the aircraft to about Mach 4.5. After the booster falls away, the scramjet is supposed to take the aircraft up to Mach 6.

Other hypersonic test vehicles have gone faster. The X-43A hit Mach 9.7. But it used hydrogen, not simple hydrocarbons, for fuel. And its engine burned away after 10 seconds. The X-51 could fly for as long as 5 minutes.

WaveRider is a collaboration between Boeing Phantom Works and engine maker Pratt & Whitney Rocketdyne. The project has been funded by the Air Force, NASA and Darpa, the Pentagon’s far-out research arm.

Video: U.S. Air Force

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