太陽能激光炮? 
Lasers to beam energy to Earth from space
Solar energy collected in space and beamed back to Earth by laser could soon be used to power homes and electric vehicles under a project by European space engineers.
By Richard Gray, Science Correspondent
Published: 8:30PM GMT 23 Jan 2010
It sounds more like a scheme dreamed up by a James Bond villain attempting to destroy the Earth than a technology that could help provide a solution to the planet's dwindling energy supplies.
Engineers plan to put satellites into orbit around the planet that can gather energy from the sun, concentrate it into powerful laser beams and transmit the energy back to the Earth where it can be used to generate electricity.
While harvesting solar energy in space has been discussed by scientists for more than 30 years, engineers at EADS Astrium, Europe's largest space company, now believe the technology is available to allow them to start building a working prototype.
They hope to have a small demonstrator of a full sized space-based power station, capable of beaming back 10-20kW of power, ready for launch in the next five years.
Using a network of these solar power stations it would be possible to provide energy on demand 24 hours a day – something that is not possible with solar power on the planet's surface which can only produce energy during the hours of sunlight.
"There is a global need for increased energy generation that does not have an environmental impact," explained Matthew Perren, head of innovation at Astrium's headquarters in Paris.
"The real advantage of space solar power is that it can provide power on demand as we can essentially point the laser beam where ever we like on the earth below the orbit.
"Looking to the future we envisage large power stations in space that are capable of transmitting energy to any point in the planet on demand."
Space-based solar power, although more expensive than using solar panels on Earth, is attractive because of its capability to provide a clean, inexhaustible power supply around the clock.
Much of the power of the sun is filtered out by the Earth's atmosphere while clouds and the inability to produce power at night have all limited the use of solar power as an energy source.
In space, however, the sun's rays are far more powerful and even with a relatively inefficient conversion process, could still produce large amounts of power. Most importantly, satellites can be positioned so they are exposed to sunlight for far longer than sites on Earth.
The space power stations would be launched into a geostationary orbit, which means they remain above the same point above the planet, around 22,300 miles above the surface.
With solar panels more than 50 metres across, they would be able to gather large amounts of energy from the sun which would then be converted into a infrared laser beam to be transmitted back to Earth.
One of the key uses of the technology could be to power a new generation of large electric vehicles such as cargo ships and tankers. The satellites could be made to move the laser beam to track the ships as they move across the ocean, providing a constant energy supply.
Scientists at Astrium have already begun work on developing the technology needed to turn a laser beam into movable source of electricity. They have managed to use lasers in the laboratory to power toy cars.
Astrium hopes to work with international space agencies, governments and power companies to develop a network of space based power stations that will eventually be capable of supplying enough energy to power hundreds of thousands of homes.
But it is not the only firm working in the field. In September Japan announced a $21 billion plan to send solar panel equipped satellite into space that could beam enough power back to Earth to supply 300,000 homes.
California has also made a deal with a company called Solaren to design satellites that would beam power back down from solar powered satellites.
But Astrium claims that its approach of using infrared lasers will make the system safer than other proposals which have suggested using microwaves to transmit the energy. If misdirected, microwaves could cause widespread damage, effectively cooking anything in their path.
Such schemes are reminiscent of far fetched plots in James Bond movies such as Die Another Day, where villain Gustav Graves builds a space based laser that he can control as a weapon, and Diamonds are Forever, where Ernst Stavro Blofeld attempts to hold the world to ransom with a laser in space.
Astrium, however, insist that the infrared laser, which is typically used in laser guidance systems for the military, will be safe. As it is beyond the visible spectrum of the human eye, it would also not be harmful to eyesight should anyone look into the beam.
Mr Perren said: "We are concentrating on developing something that is safe. While the laser beam will have some heat in it, we intend for it to be safe for people to walk through unaffected.
"Much of the technology we need has already been tried and tested in existing satellites and spacecraft, but there are technical difficulties that still need to be overcome such as improving the efficiency of converting the energy and increasing the power of the laser we can build.
"It is important to remember that we are not looking to take the place of power stations on Earth, but to provide another piece of the puzzle in finding alternative energy sources."
http://www.telegraph.co.uk/earth/energy/solarpower/7060015/Lasers-to-beam-energy-to-Earth-from-space.html
