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THE maiden flight of a paper aeroplane might not seem like much of a technological achievement, but for a team of Japanese researchers it could herald the dawn of a new way of flying: laser propulsion.

The paper plane in question is no ordinary piece of origami. Attached to its tail is a lightweight propulsion system that uses energy from a ground-based laser to propel the aircraft forward.

If the technique, called laser ablation, is scaled up to full-sized planes it should provide enough thrust to accelerate a 10-tonne plane to supersonic speeds, say its developers. They propose using it to keep fleets of spotter planes or low-altitude communication platforms circling above cities.

To power the plane, a laser on the ground is aimed at a metal plate mounted on the plane. As metal vapour produced by heat from the laser expands into the surrounding atmosphere, it produces thrust that drives the plane forwards.

The idea was first proposed in 1972 by Arthur Kantrowitz, a scientist at Dartmouth College, New Hampshire, as a way of manoeuvring satellites in space. But scientists trying to put it into practice struggled to get metal sheets to absorb enough energy from laser light to cause efficient ablation.

Now, Takashi Yabe at the Tokyo Institute of Technology believes he has found a way around the problem by coupling two materials to produce thrust for his paper plane. The target aluminium 鈥渇uel鈥� is covered by a heavier, transparent material such as perspex. Heat generated when the laser strikes the aluminium vaporises the transparent material, producing thrust. If the outer material has a low enough density this technique can be a thousand times as efficient as conventional laser ablation, says Yabe.

Working with colleagues at the Himeji Institute of Technology and the Osaka Institute of Technology, Yabe has launched his paper plane from a grooved runway by zapping it with a single laser pulse. Full-sized laser-powered planes would be lighter than conventional aircraft since they wouldn鈥檛 have to carry an engine. And because the energy source would be ground-based they wouldn鈥檛 need to carry any conventional fuel.

To scale the propulsion system up for a full-sized plane, Yabe proposes using water as the secondary propellant, since it can be harvested from the atmosphere as the plane flies. If the water is held in chambers on the trailing edges of wings, the direction of the thrust could be controlled by firing the laser at different chambers. Yabe says the laser could also be used to control altitude via shape memory alloys that change the profile of the wings鈥� trailing edges.

One difficulty with this technique will be keeping track of the vehicle with the laser to maintain thrust, says Claude Phipps of technology company Photonic Associates in Santa Fe, New Mexico. Phipps collaborated with Yabe on the laser-propelled planes, and is working independently on laser ablation to launch low-orbit microsatellites.

鈥淥bviously there has to be a clear line of sight,鈥� he says. This isn鈥檛 a big problem for vertical launches, but once the craft is flying it becomes harder to aim the laser accurately. Phipps also says you鈥檇 need 鈥渁daptive optics鈥� to counter turbulence in the atmosphere, which tends to deflect the laser beam.