The X-43 is an experimental aircraft built for NASA, who also refers to it as the
Hyper-X. It is designed solely to test the feasibility and operating characteristics of a
hypersonic SCRAMjet propulsion system and the airframe required to fly it.
There will be at least three X-43 tests (X-43A, B and C). In the first test, a B-52 test plane will drop the X-43A over the Pacific ocean. A booster rocket will fire to both lift the aircraft to its test altitude of 100,000 feet as well as to a speed high enough to ignite its SCRAMjet. If all goes well, it will accelerate under its own power to approximately 7,500 MPH (Mach 10) and maintain flight for perhaps fifteen seconds before exhausting its fuel and plunging into the Pacific. NASA does not plan on recovering it, and will be retrieving all results by telemetry. The first flight is currently (April 2001) scheduled for mid-May 2001.
A working scramjet aircraft would be extremely useful not only for high-speed transport around the globe, but also for access to space. Since a scramjet is air-breathing, the weight of consumables it is required to carry during flight in the atmosphere is dramatically cut through the elimination of liquid oxygen (LOX) supplies on board.
The current speed record for a fixed-wing aircraft is approximately Mach 6.7, set by the American X-15 test aircraft in the 1960s and 1970s. The X-15 was rocket-propelled, however, requiring both propellant and oxidizer stores to be carried onboard.