The flying prototype, called the Falcon Hypersonic Technology Vehicle 2 (HTV-2), plunged into the ocean after shifting into a mode that allows it to fly Mach 20, or about 13,000 mph, according to the Defense Advanced Research Projects Agency (DARPA), which oversaw the test flight.
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http://ca.news.yahoo.com/superfast-military-aircraft-crashed-pacific-ocean-darpa-says-210201382.html
Gravity always wins!