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Photo by: Bobbi Zapka

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

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