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Photo by: Bobbi Zapka

In this Wednesday, May 1, 2013 photo released by the U.S. Air Force, the X-51A Waverider, carried under the wing of a B-52H Stratofortress bomber, prepares to launch for its fourth and final flight over the Pacific Ocean. The X-51A, an experimental, unmanned aircraft developed for the U.S. Air Force, went hypersonic during a test off the Southern California coast, traveling at more than 3,000 mph, the Air Force said Friday. (Associated Press)

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