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