Visit our Circulation department for print subscription information. NASA said the plane, which it unveiled Wednesday, is designed to fly seven to 10 times faster than the speed of sound. Mach 1 is the speed of sound, which varies by altitude and is about 750 mph at sea level. If successful, the planes will smash the speed record of Mach 6.7, set by an X-15 in October 1967. It carries hydrogen for fuel but must scoop oxygen out of the atmosphere to combust it.
Conventional rockets carry both fuel and an oxidant.
Engineers will collect flight data needed to build future planes perhaps 200 feet in length. The first piloted prototypes may fly by 2025. Backers of the technology say air-breathing hypersonic propulsion could help space travel. Eliminating the need to carry oxygen could cut the weight of a space-faring version of such a plane in half. The X-43A, however, requires a big boost to get going.