UntitledLOS ANGELES (AP) -- A second attempt to fly an experimental unmanned jet at high speed was scheduled for Saturday, three years after the first attempt ended in an explosion.
NASA said Wednesday it hopes to reach a speed of nearly 5,000 mph (8,045 kph), or Mach 7, during its second X-43A flight. The 12-foot (3.6-meter) -long plane would fire its engine for 10 seconds, then coast for a few minutes before crashing into the ocean off California.
If the high-risk flight is successful, it will mark the first time an exotic jet engine, called a supersonic-combustion ramjet or scramjet, has propelled a plane at so-called hypersonic speeds.
Even so, the future of the $250 million Hyper-X program remains in doubt: NASA recently cut funding for more advanced versions of the plane.
NASA and the U.S. military have pursued scramjet technology because it theoretically could cut the cost of rocket-speed travel. Rockets must carry their own oxygen to combust the fuel they carry aboard, but scramjets can scoop it out of the atmosphere.
The Department of Defense is developing a hypersonic bomber that theoretically could reach targets anywhere on Earth within two hours of takeoff from the continental United States. The earliest such a plane would enter operation is 2025.
In scramjets, oxygen from the atmosphere is rammed into the combustion chamber, where it mixes with fuel and spontaneously ignites. The plane has to be traveling at about five times the speed of sound for the process to work, so it needs a conventional rocket to begin accelerating.
The first X-43A flight ended in failure June 2, 2001, after the modified Pegasus rocket that carried the plane veered off course and was detonated.
An investigation board found that preflight analyses, including wind tunnel tests, failed to predict how the rocket would perform in flight. As a result, the rocket's control system could not keep the vehicle stable, according to the board.
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