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Volume 46 | Issue 3 | April 2004


photo: x43 flies under its own power.

NASA's B-52B air-launched the stack, comprised of a modified Orbital Sciences Pegasus booster rocket with the ATK GASL X-43A testbed attached to its nose. The X-43A separated as planned and flew to Mach 7.1 under the power of its own airbreathing engine.
NASA Photo / Jim Ross

X-43A Soars

Jay Levine
X-Press Editor

A joint NASA-industry team discovered the "holy grail" of aviation March 27 when the X-43A testbed separated from a rocket booster at approximately Mach 7 - about 5,000 mph - and flew under its own power. The flight marked a world record and the first time an integrated airbreathing supersonic ramjet (scramjet) exceeded hypersonic speed (about Mach 5).

"When we saw the acceleration, we knew we had positive thrust and a fully successful flight," said NASA Hyper-X Program Manager Vince Rausch. The X-43A research, which is a part of the Hyper-X program, was conducted jointly by Langley Research Center, Hampton, Va., Dryden and an industry team.

Dryden X-43A Program Manager Joel Sitz calls hypersonics the holy grail of aeronautics because it has taken about 40 years to execute a flight research project that validates concepts developed on the ground and researched in wind tunnels, but never proven in flight.

"The scramjet is one component of a possible advanced propulsion system required for future exploration and commercial applications. The challenge for NASA and industry will be to build on this success to keep advanced airbreathing technology moving forward," Sitz said.

Because of the difficulty and length of time it has taken to meet the objectives of the successful X-43A mission, Sitz was jubilant about the breakthrough achievement: "We hit a home run in the bottom on the twelfth."

Prior to the record-breaking flight that included several firsts in aeronautics, the triple supersonic SR-71 was the fastest known airbreathing engine aircraft. The fastest rocket-powered aircraft flight within the atmosphere was the Mach 6.7 flight in 1967 by William J. "Pete" Knight in the X-15. A bullet fired from a gun travels at roughly Mach 3.

The X-43A is an unpiloted 12-foot-long vehicle. It was air launched from the wing of the NASA B-52B and rocketed to its research altitude of 95,000 feet and Mach 7 by a modified Orbital Sciences Pegasus booster rocket. From there, the ATK GASL-built X-43A separated from the booster, performed the engine test and several aerodynamic tests before reaching the intended end of its journey in the Pacific Ocean.

photo: X-43 is dropped from the mothership.

The X-43A air launch of the "stack" from the mothership.
NASA Photo / Jim Ross

Simple in concept but exceedingly difficult to design and demonstrate, a scramjet engine is not much more than a hollow tube with few moving parts. While the X-43A flew at Mach 7, air was flowing through the engine at about half that speed. Among many of the daunting challenges involved: Introduce fuel, ignite it and achieve combustion in the millisecond each individual molecule of air spends in the engine - a task that makes lighting a match in a hurricane seem tame by comparison.

On the surface, the 10 seconds of data that was gathered during the flight might seem like a small amount, but it's an eternity to researchers who will have gained valuable data they will compare to models and paradigms developed on the ground during the past four decades, Sitz said.

The team sees the flight as the beginning of hypersonic-realm discovery, as X-43A vehicle number three is presently at Dryden and undergoing preparation for flight test this fall.

"We achieved positive acceleration of the vehicle while we were climbing, and maintained outstanding vehicle control. This was a world-record speed for air-breathing flight. We had outstanding vehicle control through the entire scramjet portion of the experiment," said Larry Huebner, Langley Hyper-X propulsion lead.

"To put this in perspective, a little over a hundred years ago a couple of guys from Ohio flew for 120 feet in the first controlled, powered flight. Today, we did something very similar in the same amount of time but our vehicle, under airbreathing power, went over 15 miles," he said. "Now it's time to roll up our sleeves and start looking at some data."

Brad Neal, Dryden mission controller, shared Huebner's enthusiasm.

"It went without a hitch. It was a big operation and we've been working on it for a lot of years, and this last week we've been working round the clock. We like to have these kinds of finales to these type of operations," Neal said.

"The X-43A team believes this flight will pave the way for a new future during the next two decades," said Dryden X-43A Chief Engineer Griff Corpening. "We've shown we can fly out there."

Because the theory and design methodology is now backed up by flight research, Corpening said industry and military interests in hypersonic vehicles can now be pursued with much more confidence.

For now, however, the researchers want to savor a moment that has not been reached easily.

"It was all the sweeter for the challenges we had to step up to over the life of the program," Corpening said.

This was the second flight in the X-43A project. On June 2, 2001, the first X-43A vehicle was lost moments after release from the wing of the B-52. Following booster ignition, the combined booster and X-43A vehicle deviated from the flight path and were deliberately destroyed. Investigation into the mishap showed that there was no single contributing factor, but the root cause of the problem was identified as the control system of the booster.

ATK GASL (formerly MicroCraft Inc.) based in Tullahoma, Tenn., built both the vehicle and the engine, and Boeing Phantom Works, Huntington Beach, Calif., designed the thermal protection and onboard systems. The booster is a modified Pegasus rocket built by Orbital Sciences Corp., Chandler, Ariz.

X-43A Photo Gallery

X-43A Movie Gallery

Leslie Williams, Keith Henry and Gray Creech contributed to this report.