After the first flight attempt in June of 2001 failed when the booster rocket went out of control, the second and third attempts resulted in highly successful, record-breaking flights. Mach 6.8 was reached in March of 2004, and Mach 9.6 was reached in the final flight in November of 2004.

At nearly 5,000 mph, the March flight easily broke the previous world speed record for a jet-powered (air breathing) vehicle. The X-43A research vehicle was boosted to 95,000 feet for a brief preprogrammed engine burn at nearly Mach 7, or seven times the speed of sound. During its third and final flight -- at nearly Mach 10 -- the X-43A research vehicle flew at approximately 7,000 mph at 110,000 feet altitude, setting the current world speed record for an air-breathing vehicle.

Image above: Wind tunnel tests were a necessary step before the first flight attempt, as in this Mach 7 test of a full-scale model with spare flight engine in Langley's 8-Foot High Temperature Tunnel. Credit: NASA

The Mach 10 research vehicle featured additional thermal protection, since expected heating was roughly twice that experienced by the Mach 7 vehicle. Carbon-carbon composite material, for instance, was added to the leading edges of the vehicle’s vertical fins to handle the higher temperatures.

Both flights began with the stack being carried by a B-52B aircraft from NASA’s Dryden Flight Research Center to a predetermined point over the Pacific Ocean, 50 miles west of the Southern California coast. Release altitude from the B-52B was 40,000 feet for both successful flights. At that point, each stack was dropped and the booster lifted each research vehicle to its unique test altitude and speed.

Other than differences of altitude, speed and distance covered, the Mach 10 flight profile followed that of the Mach 7 flight: The Mach 10 research vehicle separated from the booster and flew under its own power and preprogrammed control. Shortly after separation from the booster rocket, its scramjet engine operated for about ten seconds obtaining large amounts of unique flight data for an airframe-integrated scramjet. The engine thrust was very close to its design value in each flight -- sufficient to accelerate the vehicle during the Mach 7 flight and to allow the vehicle to cruise at constant velocity in the Mach 10 flight.

In each case, when the scramjet engine test was complete, the vehicle went into a high-speed maneuvering glide and collected nearly ten minutes of hypersonic aerodynamic data while flying to a mission completion point, hundreds of miles due west (450 miles at Mach 7, 850 miles at Mach 10) in the Naval Air Warfare Center Weapons Division Sea Range off the southern coast of California. Each vehicle splashed into the ocean, as planned, and was not recovered.

Guinness World Records has recognized both the Mach 6.8 and Mach 9.6 accomplishments and has listed the flights on their web site and in the 2006 edition of their book of records. Prior to the 2004 X-43A flights, the previous record was held by a ramjet-powered missile that achieved slightly over Mach 5. The highest speed attained by a rocket-powered airplane, the X-15 aircraft, was Mach 6.7. The fastest air-breathing, crewed vehicle, the SR-71 achieved slightly over Mach 3. The X-43A more than doubled the top speed of the jet-powered SR-71.