Scientists in Australia say they've successfully tested what could be the next generation of airplane engine. Scramjets, which have been on drawing boards for several decades, could someday propel airliners at thousands of kilometres an hour.

Dr. Allan Paull, who's been testing his scramjet prototype in a wind tunnel at the University of Queensland for several years, watched Tuesday as the engine flew on the back of a rocket 314 kilometres into the air over the Australian Outback.

Paull's scramjet was released and, on the way down, ignited and flew at hypersonic speed (between 5,600 km/h to 11,000 km/h) for several seconds -- something that will be confirmed in the next few weeks when the test's data is analyzed.

"It's a world first," said Paull, who built the engine for $1.5 million, far less than the $300 million that NASA is investing in scramjet research. "We very much appreciate we're on the edge of science."

"Hopefully we’ll be in a better position to make that assessment in the next couple of days, but at the moment I’m feeling confident," he said.

NASA has called hypersonic travel "one of the greatest aeronautical research challenges."

Currently, the American SR-71 spy plane holds the record for fastest flight at 3,500 km/h or mach 3.6 (3.6 times the speed of sound).

At speeds of up to mach 10, a scramjet could potentially cut the time of a Toronto to Sydney flight from 18 hours down to three hours.

Turbojet engines are what power today's commercial jetliners. They use compressor fans (those big blades at the front of an engine) to push air into a compression chamber, where it's combined with fuel and ignited. The exhaust is forced out the back, which powers the compressor -- forcing more air into the front of the engine.

Turbojet engines are currently the most practical because they can be started while the plane is stationary.

A ramjet does away with the compressor but it must be moving at high speed to generate the pressure needed to compress the air and fuel in the combustion chamber.

A scramjet uses the same principle, except the ignition takes place while the gases are moving at above the speed of sound. Scramjets are also environmentally friendly, burning renewable hydrogen. The only exhaust gas is steam.

However, Paul cautions that the commercial applications of scramjets are likely decades away. It took almost 50 years to just to take the scramjet from theory to reality.

Because scramjets don't operate efficiently at speeds under Mach 2 or 3, a different type of propulsion will always be needed for takeoff.

Paul says the first application of scramjets will likely by the delivery of earth-orbiting satellites, since scramjets only need fuel to operate. Rockets need a combination of fuel and oxygen for thrust. The relative lightness of scramjets could cut the cost of delivering payloads dramatically.

A scramjet could take a satellite close to the edge of the atmosphere and a smaller rocket could boost it into orbit.

In June 2001, NASA launched an experimental plane called X-43a fitted with a scramjet. But before the scramjet could be activated, the aircraft had to be destroyed when it began to veer off course.