Steam power to speed up air travel

Researchers in Japan have designed a laser that could enable jet aircraft to travel in the mid and upper stratospheres within 30 years time.

Three-hour plane journeys between London and Los Angeles could become a reality, with a water-powered aircraft engine designed in Japan.

The device, which would cut over 10 hours from such a journey, generates power from a curved aluminium plate holding a small amount of water.

A beam from an infrared yttrium aluminium garnet (YAG) laser is then shot through the water and on to the aluminium dish, evaporating the metal. As the metal evaporates (a processs known as ‘ablation’), the water is turned to steam and forced out of the back of the vehicle, propelling it forward.

The system has already worked successfully in miniature during laboratory tests at the Tokyo Institute of Technology. A 0.2 joule laser was used to propel a paper plane forward for around two seconds per shot.

But at maximum efficiency, said Prof Takashi Yabe, 30 pulses from a 1MJ laser could accelerate a 10 tonne aircraft to the speed of sound. Lasers of such magnitude are already in development at the Lawrence Livermore National Laboratory in the US. The challenge will be to make them small and light enough to be carried on board an aircraft.

However, Yabe believes it would also be possible to remove the laser from the aircraft and fire it from a network of base stations on the Earth, directed at aluminium plates on the plane’s wing by positioning satellites.

He said these relatively small sized but powerful lasers would soon be available.’Lasers of several kilowatts with diode-pumped YAG laser have now been developed, and their size is only one to two metres.

‘Since the laser technology is rapidly progressing I have no doubt that 100kW lasers of similar size are no longer a dream.’

If successful, the laser powered aircraft could be flown into the mid and upper stratosphere, which lies between 20 and 40km above the Earth’s surface where normal jet engines do not work efficiently.

The stratosphere offers less resistance to aircraft than lower parts of the atmosphere, allowing greater speeds. At that height the aircraft can also take advantage of the Earth’s turn to reduce the actual distance it has to cover.This would allow the aircraft to cover large distances in a fraction of the present time.’In the lower atmosphere – the troposphere – a jet engine works best, while rocket propulsion is needed in the stratosphere. The laser-driven aircraft can work in both,’ said Yabe.

The water necessary for the process would be provided by condensation from the surrounding atmosphere.

Such transportation would not only be quieter, lighter and cheaper to operate, but would also reduce aircraft pollution levels in the upper atmosphere, thought by scientists to be a major contributor to destruction of the ozone layer.

A number of steps could also be taken to ensure passengers’ safety, should the ground-based laser fail to reach its target.

‘For safety, a booster laser can be placed inside the aircraft and can drive it from inside,’ said Yabe.

‘The laser driver is only for stratospheric purposes and the design of a hybrid aircraft would include a complementary jet engine for use within the troposphere or during an emergency.’

The technology could also be employed to propel ships or as a means of controlling the movement of telecommunications airships currently planned for installation in the stratosphere above Japan.

Yabe, who says his invention could be developed commercially within 30 years, also claims it could be used to propel robots used to clean up after a nuclear accident, where high levels of radiation render electronic devices useless.