The experimental aircraft is designed to test what is known as supersonic combustion ramjets, or scramjet technology. Unlike conventional engines, which have turbines or pistons to compress air, a scramjet engine contains few or no moving parts.
Instead, air flows powerfully into the engine's combustion chamber, where it is mixed with fuel by the forward speed of the vehicle and the shape of the inlet.
The technology holds promise for high-speed atmospheric flights, as well as for launch vehicles to carry people and payloads into space. Scramjet vehicles would be accelerated to about four times the speed of sound — sound travels at about 760 mph at sea level — by a conventional aircraft, then released for independent flights at speeds of up to about Mach 15.
In commercial terms, passenger jets could conceivably means travel from coast to coast in 20 minutes.
The advantage of scramjet vehicles is that they do not have to carry heavy oxygen tanks, but can use what is available in the atmosphere. Also, scramjets can be throttled back and flown like an airplane, as opposed to the flight of a chemical rocket, which typically is either flying full throttle or off.
Just achieving test conditions was difficult. The X-43A, for example, is mounted to a Pegasus booster rocket, then tucked beneath the wing of a modified B-52 jet for transport to an altitude of about 40,000 feet above the ocean. The B-52 drops the aircraft and about five seconds later, the rocket motor ignites to boost the X-43A to hypersonic speeds.
In Tuesday's successful test, the scramjet engine propelled the X-43A faster than its speed when the rocket engine cut off, and reached a speed of around Mach 10 — about 7,000 mph — for about 10 or 11 seconds.
"This flight is a key milestone and a major step toward the future possibilities for producing boosters for sending large and critical payloads into space in a reliable, safe, inexpensive manner," said NASA Administrator Sean O'Keefe. "These developments will also help us advance the Vision for Space Exploration, while helping to advance commercial aviation technology."
NASA has spent more than $230 million on the X-43A program and currently is fleshing out proposals for follow-on research programs.
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