X-43A aircraft (black) being accelerated by a Pegasus booster rocket (white) on 27 March 2004. After being released from the rocket, the unpiloted X-43A aircraft, or Hypersonic Experimental Vehicle (Hyper-X) reached Mach 7 (7 times the speed of sound), breaking the speed record for a jet aircraft. The X-43A is powered by a Scramjet (supersonic-combustion ramjet) engine, but requires initial rocket propulsion to reach operating speeds. Unlike rockets, scramjets use oxygen obtained from the air as the aircraft flies, potentially increasing payload. The X-43A was launched by a B-52B aircraft from Edwards Air Force Base in California, USA.