The X-43A prototype, to be launched at Edwards Air Force Base in California on March 27, supercedes one that crashed in 2001 tests.

NASA said the flight could break the speed record for a jet engine and provide greater access to space.

The current airspeed record, 3,529 kilometers (2,193 miles) per hour, or Mach 3.2, has been held by the SR-71 "Blackbird" spy plane since 1964.

Another experimental plane, the X-15, reached Mach 6.7, but with a rocket engine.

The X-43A appears futuristic, flat and small -- only 3.6 meters (12 feet) long with a wingspan of 1.5 meters (five feet).

NASA hopes to fly the plane at Mach 5 or 6,000 kilometers (3,600 miles) per hour, slightly over half of its designed capability.

The prototype is the result of 20 years of research into "scramjet" (Supersonic Combustible Ramjet) technology, which taps the atmosphere for oxygen and does away with heavy oxygen tanks used to feed rocket engines at high altitudes.

The smaller, lighter power plant allows the X-43A and its successors to dedicate that weight to heavier payloads and so reduce costs.

SPACE.WIRE