The X-43A will attempt to reach 7,000 mph, or 10 times the speed of sound (Mach 10) over U.S. Naval airspace off the coast of Los Angeles. The launch will be the third and last of a series, coming eight months after the NASA aircraft reached nearly 5,000 mph in March. Its first launch in June 2001 was aborted when its rocket booster went out of control.
The space agency is testing a type of supersonic engine that uses forward motion for power. As the scramjet propels itself at an altitude of about 100,000 feet, air flows through its engine, where it is isolated and then used for combustion when it mixes with rocket fuel. Common engines on airlines or fighter jets use fan blades to compress air.
To get up to its launch atmosphere, a B-52 bomber will first carry the X-43A, attached to a rocket, in its belly. At 40,000 feet, the B-52 drops its payload and the rocket shoots itself to an altitude of 95,000 feet, where the X-43A turns on its scramjet engine for its attempt to reach Mach 10.
If it works, NASA hopes to use the scramjet concept to build hypersonic missiles and aircraft.