Boeing X - 51 The Boeing X - 51 ( also known as X - 51 WaveRider ) is an unmanned scramjet demonstration aircraft for hypersonic ( Mach 6 , approximately at altitude ) flight testing . It completed its first powered hypersonic flight on 26 May 2010 . After two unsuccessful test flights , the X - 51 completed a flight of 300 seconds and reached speeds of over Mach 5 on 1 May 2013 for the longest duration hypersonic flight . The X - 51 is named " WaveRider " because it uses its shock waves to add lift . The program is run as a cooperative effort of the United States Air Force , DARPA , NASA , Boeing , and Pratt & Whitney Rocketdyne . The program is managed by the Aerospace Systems Directorate within the United States Air Force Research Laboratory ( AFRL ) . X - 51 technology will be used in the High Speed Strike Weapon ( HSSW ) , a Mach 5 + missile planned to enter service in the mid - 2020s . Design and development . In the 1990s , the Air Force Research Laboratory ( AFRL ) began the HyTECH program for hypersonic propulsion . Pratt & Whitney received a contract from the AFRL to develop a hydrocarbon - fueled scramjet engine which led to the development of the SJX61 engine . The SJX61 engine was originally meant for the NASA X - 43C , which was eventually canceled . The engine was applied to the AFRL ' s Scramjet Engine Demonstrator program in late 2003 . The scramjet flight test vehicle was designated X - 51 on 27 September 2005 . In flight demonstrations , the X - 51 is carried by a B - 52 to an altitude of about and then released over the Pacific Ocean . The X - 51 is initially propelled by an MGM - 140 ATACMS solid rocket booster to approximately Mach 4 . 5 . The booster is then jettisoned and the vehicle ' s Pratt & Whitney Rocketdyne SJY61 scramjet accelerates it to a top flight speed near Mach 6 . The X - 51 uses JP - 7 fuel for the SJY61 scramjet , carrying some on board . DARPA once viewed X - 51 as a stepping stone to Blackswift , a planned hypersonic demonstrator which was canceled in October 2008 . In May 2013 , the U . S . Air Force plans have X - 51 technology applied to the High Speed Strike Weapon ( HSSW ) , a missile of similar in size to the X - 51 . The HSSW could fly in 2020 and enter service in the mid - 2020s . It is envisioned to have a range of 500 - 600 nmi , fly at Mach 5 - 6 , and fit on an F - 35 or in the internal bay of a B - 2 bomber . Testing . Ground tests of the X - 51A began in late 2006 . A preliminary version of the X - 51 , the " Ground Demonstrator Engine No . 2 " , completed wind tunnel tests at the NASA Langley Research Center on 27 July 2006 . Testing continued there until a simulated X - 51 flight at Mach 5 was successfully completed on 30 April 2007 . The testing is intended to observe acceleration between Mach 4 and Mach 6 and to demonstrate that hypersonic thrust " isn ' t just luck " . Four test flights were initially planned for 2009 , but the first captive flight of the X - 51A on a B - 52 was not conducted until 9 December 2009 , with further captive flights in early 2010 . Powered flight tests . 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 postponement . The X - 51 completed its first powered flight successfully on 26 May 2010 . It reached a speed of Mach 5 , an altitude of and flew for over 200 seconds ; it did not meet the planned 300 second flight duration , however . The test had the longest hypersonic flight time of 140 seconds while under its scramjet power . The X - 43 had the previous longest flight burn time of 12 seconds , while setting a new speed record of Mach 9 . 8 ( 12 , 144 km / h , 7 , 546 mph ) . Three more test flights were planned and will use the same flight trajectory . Boeing proposed to the Air Force Research Laboratory ( AFRL ) that two test flights be added to increase the total to six , with flights taking place at four to six week intervals , provided there are no failures . The second test flight was initially scheduled for 24 March 2011 , but was not conducted due to unfavorable test conditions . The flight took place on 13 June 2011 . However , the flight over the Pacific Ocean ended early due to an inlet unstart event after being boosted to Mach 5 speed . The flight data from the test was being investigated . A B - 52 released the X - 51 at an approximate altitude of 50 , 000 feet . The X - 51 ’ s scramjet engine lit on ethylene , but did not properly transition to JP - 7 fuel operation . The third test flight took place on 14 August 2012 . The X - 51 was to make a 300 second ( 5 minutes ) experimental flight at speeds of Mach 5 , more than 3 , 600 mph . After separating from its rocket booster , the craft lost control and crashed into the Pacific . The Air Force Research Laboratory ( AFRL ) determined the problem was the X - 51 ' s upper right aerodynamic fin unlocked during flight and became uncontrollable ; all four fins are needed for aerodynamic control . The aircraft lost control before the scramjet engine could ignite . On 1 May 2013 , the X - 51 performed its first fully successful flight test on its fourth test flight . The X - 51 and booster detached from a B - 52H and was powered to by a booster rocket . It then separated cleanly from the booster and ignited its own engine . The test aircraft then accelerated to and flew for 240 seconds until running out of fuel and plunging into the Pacific Ocean off Point Mugu ; this test was the longest air - breathing hypersonic flight . Researchers collected flight telemetry data for 370 seconds . The test signified the completion of the program . The Air Force Research Laboratory believes the successful flight will serve as research for practical applications of hypersonic flight , such as a missile , reconnaissance , transport , and air - breathing first stage for a space system .