Features

EDWARDS AIR FORCE BASE — NASA on Wednesday unveiled a futuristic “scramjet”-powered aircraft designed to hurtle over the Pacific Ocean at up to 7,200 mph in a test this spring, becoming the world’s fastest air-breathing plane. 

The National Aeronautics and Space Administration’s first unpiloted X-43A will make its maiden flight in mid-May, flying under its own power for just 10 seconds and about 17 miles before coasting to a water impact off the coast of California. 

Two more X-43As will fly at six-month intervals. The 12-foot-long, surfboard-shaped planes with spatula noses and 5-foot wingspans should travel seven to 10 times faster than the speed of sound. 

“This is an aviation first in that no one has flown an air-breathing aircraft at Mach 7,” said Vince Rausch, manager of the X-43A program at NASA’s Langley Research Center. 

If successful, the X-43A will smash the speed record of Mach 6.7, set by an X-15 in October 1967. But unlike the rocket-powered X-15, the X-43A, or Hyper-X, has an air-breathing engine. It carries hydrogen for fuel, but must scoop oxygen out of the atmosphere to combust it. Conventional rockets carry both fuel and an oxidant. 

Currently, the fastest air-breathing aircraft is the SR-71 “Blackbird,” which cruises slightly faster than Mach 3.  

The X-43A should become the first air-breathing plane to go hypersonic, or faster than Mach 5. 

The government has pursued the idea of routine hypersonic flight for four decades, including an abortive $2.4 billion effort begun under President Reagan to build a “National Aero-Space Plane” capable of zipping halfway around the globe in a few hours. 

“The concept is pretty simple, it’s just that no one can seem to make it work,” said Howard McCurdy, a professor of public affairs at American University. 

The $185 million X-43A project is purely experimental. Engineers will collect flight data needed to build future planes perhaps 200 feet in length. The first piloted prototypes may fly by 2025. 

Such planes will probably never carry commercial passengers because of the high acceleration, high heat generated by friction with the atmosphere and the difficulty of turning a plane moving at those speeds. 

“This is not a very nice way to travel,” said Hans Hornung, director of the graduate aeronautical laboratories at the California Institute of Technology. 

Backers of the technology see air-breathing hypersonic propulsion as advantageous for improving access to space.  

Eliminating the need to carry oxygen could cut the weight of a space-faring version of such a plane in half. 

The X-43A, however, requires a big boost to get going. 

During the test flights, one of the same B-52s used on the X-15 program will haul the X-43A to about 24,000 feet and release it. A booster rocket will ignite to accelerate the X-43A to its test speed and altitude of about 100,000 feet.  

The X-43A will then separate from the booster and fly west over the Pacific under its own power and control. 

The X-43A needs the rocket boost in order for its specialized supersonic-combustion ramjet, or “scramjet,” engine to work. 

In normal jet engines, rotating blades do the compression work for the engine. Ramjets work through the subsonic combustion of fuel in a stream of air compressed by the forward speed of the aircraft. In scramjets, however, the airflow travels through the whole engine faster than the speed of sound. 

“The analogy is lighting a match and keeping it lit in a hurricane,” said Joel Sitz, X-43A flight test project manager at NASA’s Dryden Flight Research Center. 

In the X-43A, the shape of the plane itself forms part of the engine, with the forebody acting as the intake for the airflow and the aft serving as the nozzle. The copper engine has no moving parts other than the valves used to supply the hydrogen fuel. 

“From the nose to the tail, you basically have a flying engine,” Rausch said. 

Project officials said that using a rocket to get the X-43A up to speed is a complicated but necessary step because the scramjet propulsion system cannot be tested at such velocities in a laboratory. 

“It’s a brute-force approach to get something to test conditions,” Raush said. “For a real airplane this is a goofy way to do it, but this is research.” 

Initial plans called for the X-43As to land on San Nicolas Island, southwest of Los Angeles, but ultimately they were built without landing gear. None of the X-43As will be recovered from the ocean.