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Match in a Hurricane: NASA's X-43A Storms Into Hypersonic Realm
NASA has a long history in hypersonic flight. The record-breaking, rocket-powered X-15 reached a top speed of Mach 6.7. Hypersonic speeds are defined as those above Mach 5, or five times the speed of sound.

X-43A under B-52B wing
  The black X-43A rides on the front of a modified
  Pegasus booster rocket under the wing of
  NASA's B-52B mothership
  NASA Photo by Carla Thomas.
What's new about hypersonic flight is the advancement of the science that has enabled it to become air-breathing. Traditionally, only rocket-powered vehicles have flown hypersonically, carrying their own oxidizer along with fuel. This constitutes a large weight penalty, one that air-breathing engines can mitigate. The X-43 will scoop air molecules from the thin upper atmosphere to provide enough oxygen for combustion, instead of carrying its own along.

The X-43A, NASA's state-of-the-art hypersonic research vehicle, is designed to fly at speeds up to Mach 10, faster than any previous air-breathing aircraft. The world's fastest air-breathing aircraft, the SR-71, cruised slightly faster than Mach 3.

The key to air-breathing hypersonic flight is the X-43's scramjet engine. The scramjet, or supersonic combustion ramjet, is designed to allow the air passing through the engine to flow at supersonic speeds without blowing out the fire. It's the equivalent of keeping a match lit in a hurricane.

Unlike conventional aircraft, the X-43A will not take off under its own power. Instead, NASA Dryden Flight Research Center's B-52B aircraft will climb to about 40,000 feet to release the booster rocket, which will accelerate the X-43A research vehicle. At the test conditions of Mach 7 at 100,000 feet, the X-43A will separate from the booster and fly under its own power under programmed control.

NASA's Langley Research Center in Hampton, Va., manages and funds the X-43A project. For decades, engineers at NASA Langley have put futuristic flight vehicles through their paces in the Center's hypersonic wind tunnel.

Flights of the X-43A originate from NASA Dryden, located on Edwards Air Force Base, Calif. Launch and flight of the X-43A take place within the Western Test Range off the coast of Southern California, with the vehicle flying on a westerly heading out to sea.

NASA Dryden's vintage B-52B that will carry the X-43A to launch altitude is the oldest B-52 flying. The aircraft has been used on some of the most important projects in aerospace history. It is one of two B-52s used to air launch the three X-15 hypersonic aircraft.

The X-43A and its booster rocket, mounted beneath the wing of the B-52, completed a successful captive-carry flight on Jan. 26, 2004. A dress rehearsal for the subsequent free flight, the captive-carry flight kept the X-43A and booster combination attached to the B-52's wing pylon throughout the almost two-hour mission from Dryden. Captive-carry flights help determine that the vehicle and the team are flight-ready.

Finally, after much preparation, the X-43A is set to fly, with lessons learned and corrections made to further reduce the risky proposition of advancing the state-of-the-art in hypersonic flight.

Gray Creech, NASA Dryden Flight Research Center