"What we demonstrated is that technology we have been working for more than 40 years on the ground works," Lawrence Huebner, with NASA's Langley Research Center in Hampton, Va., told United Press International. Huebner is the lead propulsion researcher for engine design of the X-43 vehicle, which flew Saturday off the California coast.

"NASA has shown we can fly out there," added Griffin Corpening, X-43 chief engineer at NASA's Dryden Flight Research Center at Edwards Air Force Base, Calif. "Industry can now step forward with confidence that they can now use this technology."

The unpiloted, 12-foot-long aircraft actually flew at seven times the speed of sound, or Mach 7 -- nearly 4,800 miles per hour -- for about 11 seconds, then executed a preprogrammed series of aerodynamic maneuvers during the six-minute glide to splashdown in the Pacific Ocean. The aircraft was not designed to be recovered.

More important than breaking the 1964 speed record, set by an SR-71 "Blackbird" spy plane, the test proved an engine can fly at speeds exceeding Mach 5, which is referred to as hypersonic, and still scoop air from the atmosphere, rather than having to carry an oxidizer aboard, as conventional rockets must do. The savings in weight means a dramatic increase in payload capacity and range.

"The most efficient way to leave the atmosphere is to do so under air-breathing power," Corpening said at a news briefing following the flight.

The X-43 engine is called a scramjet, which stands for supersonic combustion ramjet. Rather than turbine blades, which conventional jet engines use to compress air for fuel combustion, the scramjet relies on the shape of the aircraft itself, moving at hypersonic speeds, to compress the air so fuel combustion can take place in supersonic conditions. The technology allows aircraft to fly where oxygen is sparse.

Because scramjets need to be at hypersonic speeds to work, the X-43 was carried into the sky by a modified B-52 bomber, then catapulted to Mach 7 and an altitude of about 100,000 feet by a Pegasus rocket booster. Once the booster separated, the X-43 slowed down a bit, then fired up its engine and gained speed.

"Scramjets are the holy grail of aerodynamics," said X-43 project manager Joel Sitz. "This technology will find its way into future vehicles."

Air-breathing, high-altitude cruisers are expected to bridge the gap between jets and rockets, as well as lay the foundation for a new generation of missiles and long-range, high-speed bombers for the military.

The Defense Advanced Research Projects Agency's Project FALCON, for example, is geared toward developing a piloted or unpiloted reusable hypersonic cruiser that can reach any target in the world from the continental United States within two hours, thereby reducing U.S. dependency on overseas bases and bypassing issues of national airspace.

The Blackbird, which reached Mach 3.2 -- about 2,200 mph -- during its record-breaking flight on July 28, 1976, is still the fastest plane in the world. Only two aircraft are still flying, however, conducting high-speed research for NASA. The rest of the fleet, which was used for decades for high-altitude military reconnaissance, has been retired.

In addition to DARPA's hypersonic cruise vehicle, the Air Force is working on a scramjet engine demonstrator called the WaveRider, and the Navy and DARPA are teaming for a hypersonic missile demonstrator called HyFly.

Civilian applications of supersonic transport have lagged, culminating with the retirement last year of the Concorde, the world's only commercially available supersonic jet airliner. Jets traveling at the speed reached by the X-43 on Saturday would turn a transatlantic flight into a 45-minute commute.

NASA has one more X-43 test flight planned. This summer, the agency's third and final test vehicle will attempt to reach Mach 10. The first flight of an X-43 in June 2001 ended in failure. A problem with the booster rocket forced ground control teams to destroy the craft before it reached supersonic speeds.

Among the companies closing watching the X-43 program is Boeing, which teamed with ATK GASL of Tullahoma, Tenn., to develop and build the test vehicles.

"This successful flight is an important step toward validating the use of advanced air-breathing propulsion technology for achieving more rapid global travel and routine, affordable access to space," said Bob Krieger, president of Phantom Works, Boeing's advanced research and development unit.

Hypersonic flight is a challenge not only for propulsion, but also for materials and aerodynamic control. At such speeds, metals can melt or vaporize almost instantly and there is little margin for error in control. Designers also must account for shock waves that can severely affect parts of the airframe due to high heating and force.

The X-43 program, which is costing NASA about $230 million, is the agency's first venture into hypersonic flight since the cancellation of the X-15 program 35 years ago. That program culminated in a 1969 flight clocked at Mach 6.7 -- about 4,500 mph -- but unlike the X-43, the X-15 used rockets for propulsion.

"Our vehicle under air-breathing power went over 15 miles," said Huebner. "The flight was the first-ever airframe integrated scramjet engine experiment. We can claim an air-breathing powered record today -- no doubt about it."

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