Tucked beneath the 25-metre-long left wing of the aircraft was a 7.6-metre unmanned craft designated X-51A Waverider, on the fourth and fi nal fl ight of a test programme conceived by researchers at the United States Air Force Research Laboratory to probe the limits of socalled ‘hypersonic’ fl ight, in excess of fi ve times the speed of sound. 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.On the morning of, a 50-yearold B-52 bomber took off from Edwards Air Force Base in the high desert of California, bound west towards the Pacifi c Ocean. 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. 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. But the mission ended in disaster even before the scramjet could fire up. 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. 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. 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. 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). 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. The X-43A, a 3.7-meter-long, unpiloted research vehicle, is the current focus of the $185 million effort. 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. 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. In its maiden test flight last June, a hypersonic plane developed by NASA veered off course and was destroyed.
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January 2023
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