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The first HTV-2 was launched on April 22, 2010. It returned nine minutes of data, including 139 seconds of aerodynamic data at speeds between 17 and 22 times the speed of sound, DARPA said.

That craft detected an anomaly, aborted its flight and plunged into the ocean, the agency said.

The military and NASA have also been working on powered aircraft capable of flying at speeds greater than five times the speed of sound, or Mach 5.

In 2004, NASA’s unmanned X-43A reached Mach 9.6 on a flight off California. Powered for 10 seconds by a supersonic combustion ramjet, or scramjet, that set a speed record for jet-powered flight.

The X-43A also set the previous record of Mach 6.8 earlier that year.

The unmanned X-51A Waverider, a demonstrator, developed by the Air Force, DARPA, Pratt & Whitney Rocketdyne and Boeing, has been tested twice.

Powered by a scramjet, the first X-51A reached about Mach 5 for 140 seconds after being dropped from the wing of a B-52 in May 2010, according to Boeing. Last June, a second craft had problems in a flight off the California coast and the test was terminated. Two more flights are planned for the X-51A program.

The HTV-2 was launched atop a Minotaur 4 rocket built by Orbital Sciences Corp. from decommissioned Peacekeeper intercontinental ballistic missiles. The Minotaur 4 made its debut last year carrying the first HTV-2.

“From what we can tell based on preliminary data, it looked like the rocket did its job,” said Orbital spokesman Barry Beneski.

Minotaur 4 is part of the Minotaur rocket family. There have been 22 Minotaur launches since 2000 _ a 100 percent success rate. The price of a single flight ranges from $15 million to $30 million depending on the rocket style, according to the company.

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AP Science Writer Alicia Chang contributed to this report.