X-51A Waverider hypersonic aircraft

A flight test of the the X-51A Waverider scramjet experimental aircraft, ended abruptly as a faulty control fin caused the craft to be lost over the Pacific.  Artists concept of the X-51A Waverider. Credit: US Air Force

The X-51 Waverider, a cooperative effort of the Air Force, DARPA, NASA, Boeing and Pratt & Whitney Rocketdyne, was dropped from a B-52 bomber off the coast of California, at an altitude of 15,240 meters (50,000 ft.), but a faulty control fin prevented it from starting its unique “airbreathing” scramjet engine.

The hypersonic vehicle is capable of hitting a top speed of Mach 6 (4,300mph / 6,900km/h).

via universetoday