The experimental X-51A Waverider was designed to reach six times the speed of sound after being released by a B-52 bomber off the Southern California coast Tuesday. The Air Force said the experimental aircraft successfully separated from the B-52 and ignited its rocket booster as planned.
But before it could activate its exotic scramjet engine, which should have taken it to Mach 6, a problem with one of its cruiser control fins caused it to lose balance and crash into the Pacific.
Officials "will now begin the process of working through a rigorous evaluation to determine the exact cause of all factors at play," Wright-Patterson Air Force Base said in a statement released Wednesday.
Tuesday's test flight was the latest loss for the Pentagon, which has been testing ever-faster aircraft in hopes of being able to deliver military strikes around the world within minutes.
Boeing Co. built four Waverider vehicles, designed for one-time use ending with a plummet into the ocean after a flight. The Air Force said no decision has been made yet whether to fly the remaining aircraft.
The first X-51A reached near five times the speed of sound for three minutes in 2010. During a test last year, a second X-51A unsuccessfully tried to restart its engine and crashed.