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MIT Technology Review

Second Chance for Scramjet

NASA’s fastest jet blew up in its maiden flight. Now, scientists say they know what happened and are ready to try again.

April 1, 2002

In its maiden test flight last June, a hypersonic plane developed by NASA veered off course and was destroyed. Despite the failure, the agency is now trying to breathe new life into its tests of the craft’s novel jet engine, called a scramjet. NASA expects that future versions of the engine will serve as a low-cost way to get payloads into orbit by lifting space cargoes to nearly stratospheric altitudes before they continue their journeys on rocket power.

The X-43A, a 3.7-meter-long, unpiloted research vehicle, is the current focus of the $185 million effort. A conventional jet engine, with its spinning blades and turbines, would tear apart at lower speeds than those envisioned for the X-43A; but the scramjet has no moving parts. That means air can safely rush through it at many times the speed of sound, combusting with hydrogen fuel to boost the vehicle to hypersonic speeds (above Mach 5). Of course, conventional liquid-fueled rockets fly even faster, but they must carry both fuel and the oxygen needed to burn it-an expensive proposition. A future craft with both scramjet and rocket power could travel to the edge of space before firing its rockets, requiring less oxygen and leaving more room for the payload.

To test that theory, NASA contractors built three X-43As; the first was to have flown last June, becoming the first air-breathing craft to fly at hypersonic speeds. But the mission ended in disaster even before the scramjet could fire up. The craft’s Pegasus booster rocket-built by Dulles, VA-based Orbital Sciences to carry the X-43A to 29,000 meters and Mach 7 before its scramjets ignited-went violently out of control just seconds after the two mated vehicles were released from their B-52 carrier plane, forcing mission controllers to send an auto-destruct signal.

Late last year a NASA investigative board tentatively blamed the disaster on the Pegasus rocket, ruling out the X-43A as the cause of the failure. Charles R. McClinton, technology manager for the scramjet program at the NASA Langley Research Center in Hampton, VA, says, “We’re convinced that we can be back to flying by the end of this year.” If the agency does get its craft off the ground, those waiting for a cheaper, more efficient way into space can begin to breathe easier.