NASA’s supersonic surfboard, the unmanned X-43A aircraft, streaked into history yesterday, setting an unofficial world speed record for jet aircraft of Mach 9.6, or about 6,500 mph.The aircraft—powered by an experimental engine known as a scramjet—was carried to an altitude of 40,000 feet under the wing of a B-52 bomber and released at about 2.30 pm. A Pegasus rocket booster accelerated the X-43A before the scramjet on the underside of the aircraft took over, shooting the craft to its record-breaking run at 111,000 feet.‘‘We had a phenomenal flight today. Everything went really well,’’ said Laurie Marshall, the chief engineer for the flight. The flight was part of a $230 million project aimed at showing the capabilities of a new breed of jet aircraft that conceivably could speed passengers across country in minutes and send passengers into space far more cheaply than today.The heart of the X-43A is its revolutionary scramjet—a contraction of Supersonic Combustion Ramjet. The engine compresses air at hypersonic velocities and ignites it in a hydrogen mixture. Most commercial aircraft today use turbines to compress air, which ignites with kerosene to create combustion and thrust. Engineers developed the ramjet decades ago to solve those problems. A ramjet is basically a hollow tube with no moving arts; air flows into the front of the ramjet, is compressed and mixed with fuel. But the ramjet cannot go faster than Mach 5, or five times the speed of sound.Compared to rocket-powered vehicles like the space shuttle, scramjet vehicles promise more airplane-like operations to improve safety and keep costs down on future hypersonic flights either in or below orbit.During its 10-second engine burn yesterday, the X-43A travelled nearly two miles a second. At that speed, a trip to New York from Los Angeles would take about 20 minutes.There remain a number of hurdles, however, before scramjets could be introduced to commercial flight. The primary one is that the engine won’t work at speeds less than Mach 4. One answer might be to include more conventional engines on board to lift the plane off the ground. Another solution would be to attach it to a rocket, though that would require future passengers to become comfortable with the chin-stretching forces of rocket takeoffs.In the near future, scramjets are more likely to be used on bunker-busting type missiles.
