text: This Air Force illustration depicts the X-51A Waverider scramjet vehicle during hypersonic flight during its May 26, 2010 test. Powered by a Pratt & Whitney Rocketdyne SJY61 scramjet engine, it is designed to ride on its own shockwave and accelerate to about Mach 6. (Credit: http://www.space.com/8617-air-force-sees-hypersonic-weapons-spaceships-future.html