In the language of Beltway defense wonkery, the results of this year's test launch of the hypersonic unmanned U.S. aircraft designated Falcon HTV-2 might be called sub-optimal.
In plain English, it appears certain that the experimental space plane - a key element of U.S. efforts to develop a conventional weapon that can strike anywhere in the world in less than an hour - disintegrated and burned up in the upper atmosphere in a failure that casts a question mark over the program's future.
The Defense Advanced Research Projects Agency (DARPA), which conducted the test flight, would say only that an engineering review board is examining data from the test flight.
Contact with the Falcon was lost about nine minutes into the half-hour flight on April 20, DARPA spokesman Eric Mazzacone said.
"The test went well for nine minutes," former Air Force chief scientist Mark J. Lewis told The Washington Times. "After that, not so well."
Mr. Lewis, who followed the $308 million project closely in his official capacity and has continued to do so since leaving the Air Force two years ago, stressed that it was "dangerous to speculate" on the causes of the failure.
"Once there's some sort of failure, the vehicle isn't going to last very long," given its enormous speed and altitude, he said. "If anything goes wrong, there's not going to be anything left of the vehicle," because the pieces would burn up on re-entry.
Richard P. Hallion, a former chief historian of the Air Force and a self-proclaimed evangelist for hypersonic vehicles, told The Times that the review would be "very carefully and thoroughly examining all possible data about this loss."
"There are many things that could have gone wrong," he said. "Those studying this are likely trying to find out whether this is a straightforward fix or something more serious that might endanger any future attempts to fly this vehicle."
The Falcon is a suborbital vehicle launched on a solid-fuel rocket booster made from a decommissioned ballistic missile. Just outside the atmosphere, in a procedure called "clamshell payload fairing release," the launch vehicle deploys the plane, which then is supposed to glide back to earth at more than 13,000 mph - more than 15 times the speed of sound.
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