The Boeing X-51A WaveRider hypersonic vehicle, powered by a Pratt & Whitney Rocketdyne scramjet engine, achieved aviation history this week by making the longest ever combustion ramjet-powered supersonic flight. During its first jaunt, the craft reached 70,000 feet and an approximate speed of Mach 5 on a 200-second flight over the Pacific Ocean on May 26 at 10 a.m. before it was purposely crashed into the water.

During its first flight, the unmanned WaveRider was carried beneath a U.S. Air Force B-52H and dropped from an altitude of about 50,000 feet over the Pacific Ocean off Southern California. A solid rocket booster fired and propelled the cruiser to speeds greater than Mach 5, creating the supersonic environment necessary to operate the engine.

The booster was then jettisoned and the Pratt & Whitney Rocketdyne SJY61 scramjet engine ignited, initially on gaseous ethylene fuel. Next the engine transitioned to JP-7 jet fuel, the same fuel used by SR-71 Blackbirds.
The USAF has three more X-51As that it plans to test at hypersonic speeds later this year.