NASA's hypersonic research aircraft that broke the world speed record in March 2004. It flew at Mach 5, just over seven times the speed of sound, or about 8 000 kph. The experimental craft, which is 3.56 m long, was launched from a converted B-52 bomber on top of a Pegasus booster rocket off the coast of southern California. It flew on its own power for six minutes, reaching an altitude of nearly 30 500 m.

The X-43A, known as a ramjet or scramjet, burns hydrogen mixed with oxygen from the atmosphere. Heavy fuel tanks are not needed. The first X-43A flight, on 2 June 2001, failed after its Pegasus rocket veered off course. The second X-43A was flown successfully on 27 March 2004, setting a record speed of Mach 6.83, about 7 900 kilometres per hour. This was the first time a scramjet engine had ever operated in flight. The third (and final) X-43A flight was made on 16 November 2004 and reached a speed of Mach 9.6, or almost 11 265 km per hour.