The Boeing X-51A Waverider is an experimental aircraft cooperative effort of the United States Air Force, DARPA, NASA, Boeing and Pratt & Whitney Rocketdyne. It is a scramjet aircraft that capable of traveling in Mach 6 or around 6,400 km/h in its last successfully first free flight on 26 May 2010. The program is managed by the Propulsion Directorate within the United States Air Force Research Laboratory (AFRL). The X-51A had its first captive flight attached to a B-52 in December 2009.