About $320 million in U.S. taxpayer dollars has gone into two hypersonic aircraft designed and built by a defense research agency -- which launched each experimental vehicle in separate tests and then promptly lost contact with them, as they barreled into the Pacific Ocean.

The latest unmanned Falcon Hypersonic Technology Vehicle-2 -- a test rocket designed to fly at Mach 20, or around 13,000 miles per hour -- successfully launched at approximately 7:45 a.m. PDT Thursday and separated properly from the Minotaur IV rocket that carried it to the edge of space. But after 2,700 seconds of flight, the agency lost contact with the vehicle, which presumably sank in the blue waters of the Pacific Ocean.