SYDNEY, Australia (Reuters) -- Japan conducted a successful test flight of a supersonic jet in the Australian outback on Monday, taking a step closer to its goal of developing a successor to the Concorde.The Japan Aerospace Exploration Agency (JAXA) said the prototype supersonic jet was launched on the back of a rocket from the remote Woomera rocket range in the South Australian desert and completed a 15-minute flight.Japanese developers hope that a new supersonic jet could some day make the trip from Tokyo to New York in just under six hours -- less than half the current time."We were able to conduct a test flight and to gather data as planned. We think we have marked a major step in the development of (supersonic flight) technology," Kimio Sakata, executive director of JAXA, told reporters in Tokyo via audio link from Australia.JAXA hopes that its research will eventually lead to the development of a commercially viable supersonic jet after clearing technological hurdles such as improving fuel efficiency and reducing noise levels, agency officials said.It will "probably take another 15 years" for the project to become commercially-viable, Sakata said.But doubts have been raised about whether the project will ever be commercially viable given that the Concorde, which was retired two years ago, never managed to turn a profit.The new jet would carry 300 passengers, three times as many as the Concorde, and travel at Mach 2, or twice the speed of sound, roughly the same as the Concorde.The Concorde was developed jointly by Britain and France in the 1960s. In July 2000, a Concorde taking off from Paris crashed, killing 113 people.A previous test in 2002 ended disastrously when the unmanned prototype dived to earth and exploded in the Australian desert.The 2005 flight at Woomera, an abandoned British rocket testing range populated with kangaroos and located in some of Australia's harshest desert, was delayed several days due to bad weather.JAXA's video footage showed the 11.5-meter (38 feet) dart-like model jet riding piggy back on the back of a rocket, and soaring into a clear, blue sky as the rocket booster left behind a trail of thick, grey smoke.The jet climbed to about 20 km (12 miles) above the Earth on the back of the rocket and then detached. It reached around twice the speed of sound and glided back to Earth using parachutes, JAXA officials said.A picture released by JAXA showed that the jet returned to earth intact this time with no obvious signs of damage.Data gained through the test will be used in joint research by Japan and France towards a next-generation supersonic jet following an agreement between the two nations in June, though the test itself is not a result of the agreement.Despite the successful test flight, however, Japan will not immediately embark on joint international development, Sakata said, adding that more work was needed first.No budget projections have yet been made for the entire project, but the costs are considerable.Copyright 2005 Reuters. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.