The Boeing X-51 Waverider is an unmanned research scramjet experimental aircraft for hypersonic flight at Mach 5 (3,300 mph; 5,300 km/h) and an altitude of 70,000 feet (21,000 m).

Waverider refers in general to aircraft that take advantage of compression lift produced by their own shock waves.

The X-51 program was a cooperative effort by the United States Air Force, DARPA, NASA, Boeing, and Pratt & Whitney Rocketdyne.

[5] In flight demonstrations, the X-51 is carried by a B-52 to an altitude of about 50,000 feet (15 km; 9.5 mi) and then released over the Pacific Ocean.

The booster is then jettisoned and the vehicle's Pratt & Whitney Rocketdyne SJY61 scramjet accelerates it to a top flight speed near Mach 6 (4,000 mph; 6,400 km/h).

[10] In May 2013, the U.S. Air Force planned to apply X-51 technology to the High Speed Strike Weapon (HSSW), a missile similar in size to the X-51.

It was to have a range of 500–600 nautical miles (930–1,110 km), fly at Mach 5–6, and fit on an F-35 or in the internal bay of a B-2 bomber.

[19][20] The first powered flight of the X-51 was planned for 25 May 2010, but the presence of a cargo ship traveling through a portion of the Naval Air Station Point Mugu Sea Range caused a 24-hour delay.

[23] The X-43 had the previous longest flight burn time of 12 seconds,[23][24][25] while setting a new speed record of Mach 9.68.

However, the flight over the Pacific Ocean ended early due to an inlet unstart event after being boosted to Mach 5 speed.