Scientists with the US space agency Nasa have taken an old idea as they try to develop new ways of travelling into space.

They hope magnetic levitation - or maglev - could help launch spacecraft into orbit using magnets to float a space vehicle along a track.

The concept is already widely used in amusement parks and Nasa has enlisted the help of a fairground ride manufacturer, along with a university in the UK.

Magnetic levitation uses an ordinary electrical motor which normally converts electricity into rotary energy.

But in this case the motor - formed from magnets - is unrolled so that it is flat.

If a metal object is then held above the spaced-out magnets, it will float in the air, levitated by the magnetic fields.

Cut-price space travel

Nasa experts believe that magnetic levitation could slash the cost of space travel.

The agency's Advanced Space Transportation Program at the Marshall Space Fight Center in Alabama is behind the project.

"Magnetic levitation is a promising technology for future space transportation as we build the highway to space," said Garry Lyles, manager of the Advanced Space Transportation Program.

"The most expensive part of any mission to low-Earth orbit is the first few seconds - getting off the ground. Maglev is a low-cost alternative for space transportation because it leaves the first-stage propulsion system on the ground."

How spacecraft could be launched by magnets

High-strength magnets are already used to lift and propel high-speed trains and roller coasters a couple of inches above a guideway.

A maglev launch-assist system would be used to drive a space vehicle down a track in a similar way, but at speeds of 600mph.

A rocket engine would then take over to enable spacecraft to reach orbit.

"A maglev system is virtually maintenance-free because it has no moving parts and there's no contact," said Mr Lyles.

"It could help launch a spacecraft from a typical airport runway to low-Earth orbit every 90 minutes."

Large scale

Experiments to test the theory have been carried out the University of Sussex in England.

In a laboratory there, a two-feet-long sled is propelled at 120mph along a 20-feet electromagnetic track.

Motors for the experiment were developed by PRT and funded by Arrow Dynamics Inc.of Utah, an amusement ride manufacturer.

As part of a larger scale experiment in 1999, two longer tracks measuring 50 and 400 feet are planned in Huntsville.

Design plans will soon be completed for a 5,000-foot track capable of launching a 40,000lb payload at a test site.

Some scientists believe that as early as 2007, a maglev launch assist system could be used to launch very small communications satellites for thousands of dollars per pound, far cheaper than current costs.