The pilotless scramjet screeched across the Pacific Ocean with NASA scientists nervously monitoring its second test flight. It was the second record to be claimed in eight months.

"It's a great day," said NASA spokeswoman Leslie Williams.

"Once again we have made aviation history," added Vincent Rausch, the X-43A program manager, who spoke after it was announced that the scramjet had nearly reached Mach 10, or almost 3.2 kilometers (two miles) per second.

"This flight is a key milestone and a major step toward the future possibilities for producing boosters for sending large and critical payloads into space in a reliable, safe, inexpensive manner," NASA Administrator Sean O'Keefe said in a statement.

"These developments will also help us advance the Vision for Space Exploration, while helping to advance commercial aviation technology," he said.

The small jet was launched from a B-52B aircraft over the Pacific. The scramjet is only 3.65 meters (12 feet) long, with a wingspan of 1.5 meters (five feet).

It beat a record set in March by another X-43A, which powered up its scramjet engine and performed "flawlessly" for 11 seconds, attaining speeds of seven times the speed of sound, or Mach 7.

The scramjet, or supersonic combustion ramjet, uses a new type of engine that burns fuel in a stream of air compressed by the forward speed of the aircraft.

NASA said scramjets will ultimately provide safer and more affordable high-speed flight in vehicles more like airplanes than rockets. Unlike rockets, scramjets can be throttled back and flown like an airplane.

NASA called it a "high-risk, high-payoff research program."

The 230-million-dollar (177-million-euro) project spans 20 years of research. Other countries, including France and Japan, are also exploring scramjet technology.

The US Air Force is seeking to develop an airplane capable of reaching any point on the globe in under two hours while transporting six tonnes of bombs or cruise missiles.

The Pentagon and the Australian Defense Ministry plan to test a similar vehicle at Mach 10 in Australia in 2005 in a jointly financed project. They hope to use the technology to put satellites in orbit.

The X-43A is the first ramjet capable of drawing its oxygen fuel directly from the atmosphere as it travels at very high speed, as opposed to rockets, which must transport huge tanks of oxygen to create combustion by mixing it with hydrogen.

NASA has built three X-43s. The first had to be destroyed in flight in June 2001. The second broke the world speed record on March 27 of this year.

NASA had to modify the last member of its X-43 fleet to withstand the high temperatures expected at Mach 10.

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