The scramjet needs to reach Mach 5 to start working

But the Australian scientists were unable to say on Tuesday if the scramjet had at any point flown under its own power. Project spokesman Peter McCutcheon said: "We're still analysing data... we're not sure, yet, if it was successful."

If the experiment was successful, the scramjet would have started to work under its own power for just a few seconds before the rocket returned to Earth. The scientists will be looking at their data on the way the rocket behaved during these crucial few seconds to decide whether or not the scramjet worked.

Scramjet mission profile

They hope to make an announcement on Wednesday.

Experts say scramjet technology has the potential to reduce the flying time from London to Sydney to two hours, and substantially cut the cost of space launches.

Traditional approach

Scramjets are simple in theory; they have no moving parts and grab the oxygen needed to combust fuel from the atmosphere.

We've bought a lot of bits and pieces off the shelf from automotive shops

Allan Paull, University of Queensland

That makes them more efficient than conventional rocket motors, which carry their own oxygen supply on board, adding weight and cutting the potential payload. But the big problem is that scramjets only start to work at speeds greater than five times the speed of sound, or Mach 5.

A few weeks ago, the Defense Advanced Research Projects Agency in the United States launched a scramjet from a gun. The Americans say their experimental engine flew under its own power for a fraction of a second - a world first.

The university has been working on scramjets for 16 years

A Nasa scramjet test in June failed when the missile that was intended to bring the engine up to its operating speed went off course.

The engine tested at Woomera was built by an international consortium led by researchers at the University of Queensland and is jokingly referred to as a "scroungejet".

"Ours is a low-cost alternative, and we've had to develop all sorts of ancillary equipment on the cheap," said Allan Paull, project head at the university.

"We've bought a lot of bits and pieces off the shelf from automotive shops," he added.

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