Flight of the X-43 vehicles will be the culmination of over 20 years of scramjet (supersonic combustible ramjet) research and the first time a non-rocket engine has powered vehicles at hypersonic speeds.

Built by Micro Craft, Inc., Tullahoma, Tenn., for NASA's Hyper-X program, the 12-foot-long, unpiloted X-43 vehicles will significantly expand the boundaries of air-breathing aircraft. Three flights are planned -- two at Mach 7 and one at Mach 10. The flight tests will be conducted within the Western Test Range off the coast of southern California.

The Hyper-X program will build a technology bridge to reusable and recoverable vehicles with larger engines. Program managers hope to demonstrate hydrogen-powered, air-breathing propulsion systems that could ultimately be applied in vehicles from hypersonic aircraft to reusable space launchers.

Hypersonic speed is reached when velocity is above Mach 5 -- equivalent to about one mile per second, or 3,600 miles per hour at sea level. The highest speed reached by NASA's rocket-powered X-15 was Mach 6.7. Currently, NASA's SR-71 is the world's fastest air-breathing aircraft, soaring slightly above Mach 3, or three times the speed of sound.

Unlike a rocket that must carry its own oxygen for combustion, an air-breathing aircraft scoops air from the atmosphere, making the aircraft lighter and enabling it to carry more cargo/payload than rocket-powered propulsion vehicles. The X-43 will use the body of the aircraft itself to form critical elements of the engine with the forebody acting as the intake for the airflow and using the aft section as the nozzle.

"This is high-risk technology. It's exactly the type of flight research that NASA's Office of Aero-Space Technology should be doing," said Joel Sitz, Dryden's X-43A project manager. "NASA, working with industry, must answer the mail on developing a feasible, efficient design."

"We have the best-performing engine in the last 30 or 40 years here at Langley," said Vincent Rausch, Hyper-X program manager. "We are excited that we have a vehicle at Dryden, but there is a lot of hard work and testing yet to be done."

Each Hyper-X vehicle will ride atop a booster rocket from Orbital Sciences Corp., Dulles, Va., and will be air-launched by Dryden's B-52 airplane. After being launched from the B-52, the X-43 will separate from the rocket at a predetermined altitude and velocity, then fly a pre-programmed trajectory, conducting aerodynamic and propulsion experiments, before it impacts into the Pacific Ocean.

NASA's Langley Research Center, Hampton, VA, where the X-43's engine -- scramjet -- is being wind-tunnel tested, manages the Hyper-X program. Dryden is responsible for vehicle fabrication and flight tests.