The Air Force has suffered another setback to its attempts to build a plane that could reach anywhere in the world within an hour.
The X-51 A - known as Waverider - failed and crashed into the Pacific just moments after launch yesterday.
It separated from its carrier B-52 bomber successfully, and the rocket booster fired as planned - but a problem with the cruiser control fins caused it to be lost just 16 seconds after takeoff.
"It is unfortunate that a problem with this subsystem caused a termination before we could light the Scramjet engine," says Charlie Brink, X-51A program manager for the Air Force Research Laboratory.
"All our data showed we had created the right conditions for engine ignition and we were very hopeful to meet our test objectives."
The Air Force says the plane is designed to pave the way to future hypersonic weapons; hypersonic intelligence, surveillance and reconnaissance; and possibly space travel.
It's around 25 feet long and includes a modified solid rocket booster from an Army Tactical Missile, a connecting interstage, and the X-51A cruiser. Almost wingless, it's designed to ride its own shockwave - hence the name.
It has small, controllable fins and is based around an SJY61 supersonic combustion ramjet or scramjet engine built by Pratt & Whitney Rocketdyne and designed to burn JP-7 jet fuel. It was designed, assembled and developed by Boeing.
Waverider has a history of failed tests. Its first, in May 2010, did succeed in getting the plane up to Mach 5 in a three and a half-minute flight that was the longest supersonic combustion ramjet-powered flight in history. However, it lost acceleration, suffered heat damage and was destroyed. A second test flight in June last year also failed.
With only four of the planes built, the Air Force now has just one left. Let's hope it looks after it very carefully.