On Tuesday, the U.S. Air Force and NASA conducted a key test of an experimental unmanned aircraft designed to fly at six times the speed of sound, or about 3,600 mph (5,800 kph). Off the Southern California coast near Point Mugu, the unmanned X-51 WaveRider was expected to reach Mach 6, after being dropped by a B-52 bomber flying at 50,000 feet (15,250 meters) and engaging its rocket engine. An hour of travel at this speed would get the aircraft from London to New York. The aircraft is incapable of taking off on its own, nor can it land. It has to be propelled by another aircraft in midair, and when it runs out of fuel, it simply falls into the ocean. The technology behind the X-51's scramjet propulsion include a new jet fuel system. Unlike normal engines, which use both fuel and oxygen (required for ignition) in the tank, the X-51's tank has only liquid fuel and extracts its oxygen from the atmosphere. Engineers hope that the hypersonic X-51 would sustain its top speed for five minutes, twice as long as it has gone before. The B-52 took to the skies Tuesday, but no other information about the test flight was available, John Haire, a spokesman for Edwards Air Force Base in California, said in an email. Last year, in its most recent test, the X-51 fell for about four seconds before its booster rocket ignited, but the aircraft failed to separate from the rocket and plunged into the ocean. Designed by Boeing Co., the aircraft is intended to allow the Pentagon to deliver missile strikes around the globe within minutes.
