The Air Force’s X-51A hypersonic test drone crashed just 15 seconds after it started its flight high above the Pacific Ocean this week. The WaveRider’s control fins stopped working after it had been dropped from a plane and after its rocket had engaged, starting to accelerate the aircraft. The WaveRider was slated to accelerate to Mach 6 during a five-minute test flight powered by a scramjet engine, but the flight didn’t last long enough for that engine to engage. The WaveRider’s three test flights have now all faced problems. The first flight, in 2010, suffered from a remote data sensing problem three minutes into the flight. And in last year’s test, unexpected shockwaves caused airflow problems for the scramjet, which had to be shut down prematurely. The control fins had never posed problems before this week’s failed test, sending engineers back to review data about what went wrong with the test.