Pratt & Whitney Rocketdyne/Boeing X-51A Waverider

After dropping from a B-52 bomber 50,000 feet above the Pacific in May, the unmanned X-51A WaveRider destroyed the scramjet endurance record by flying at five times the speed of sound for more than three minutes. Despite five decades of research, engineers had previously never able to keep a scramjet (an engine that generates rocket-level speed by massively compressing air from the atmosphere) going for more than 12 seconds. That’s because the air that feeds combustion in a scramjet moves through the engine at supersonic speed; the challenge is to keep that air feeding the burning fuel rather than snuffing it out.
A new engine geometry and precision fuel injection made the record possible. The project, funded by the U.S. Air Force and the Pentagon’s Darpa, is a step toward developing advanced cruise missiles and cheaper space transport. pwrhypersonics.com