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Reply	Bugs says: As the coil moves through the Earth's magnetic field a current would be induced in it, which we could beam down to the surface or use to power our satellite. Unfortunately, this current would create its own magnetic field around the coil, opposed to the Earth's. This would act as a brake, slowing the satellite down so it falls into a lower orbit and - eventually - back down to Earth. You could burn fuel to speed the satellite back up, but this would take at least as much energy as the satellite generated while it was slowing down. Thinking about fuel, conservation of enery means that the energy you'd spend lifting it up into orbit and then accellerating it to the necessary speed would have to be at least equal to the energy that could be extracted as it slowed back down and fell to earth. Given that there's no way we could work the systems involved at 100% efficiency, you'd be much better off just burning the rocket fuel in turbine hooked to the national grid.Still, if you could manufacture these in space and accellerate them into orbit using some sort of gravity slingshot, you might be able to generate more energy before they fall than was expended getting them there in the first place. As a bonus, the regular burn-ups of coils falling into the atmosphere would look spectacular.Christopher Binny  (no votes) Tags: technology, planet earth.
	posted on 2007-06-22 22:54:00 | Report abuse

Reply	Michael says: The following answer was selected and edited by New Scientist staffYou can't get electrical energy for free; some other form of energy must be drained. When a coil moves though a magnetic field, the electric current that this induces generates a force that acts to oppose the motion of the coil. So in a dynamo, for instance, an external form of mechanical energy is needed to keep the coil spinning. In a coil orbiting Earth, the induced force would slow the coil down, causing it to fall from orbit and plunge to Earth.If you mounted a rocket on the coil to keep it in orbit, you would find that the amount of electrical energy generated would never exceed the amount of energy you spent keeping the coil in orbit, not to mention the exceedingly large amount of energy required to get it into orbit in the first place. So sorry, no Nobel prize.Simon Iveson, Mayfield, New South Wales, Australia  (no votes) Tags: technology, planet earth.
	posted on 2007-08-01 17:29:00 | Report abuse

Reply	Michael says: The following answer was selected and edited by New Scientist staffThis idea would waste far more energy than you could ever generate from the coil. It is not without merit, however. NASA has experimented with conductive tethers in orbit. They have tried using them both to generate electricity from the motion of a satellite around the Earth and, by reversing the process, to change the orbit of a satellite around Earth by passing electricity through the tether (see New Scientist, 17 February 1996, p 23 and 2 March 1996, p 13). They were not successful, and neither were more recent efforts - see this article.Jon Webb Pittsburgh, Pennsylvania, US  (no votes) Tags: technology, planet earth.
	posted on 2007-08-01 17:33:00 | Report abuse

Reply	Anonymous says: As the other responses have stated - placing a coil in orbit is a waste of rocket fuel. That said, many people have seriously considered the idea of placing solar arrays in space for bulk electrical collection. Solar panels in space are a factor 30% more illuminated. This is one of the prime ideas for uses of the space elevator. It is unfortuante though - I ball park the costs are 493 million per megaWatt, plus the RD costs of the microwave system. If you could decrease the launch costs to a small fraction though - say under 3 million(they currently sit at about 485 million), you could easily complete this more cheaply in orbit then on the ground. With an S.E., you find this happens quite easily with the price estimates at hand of 100$/kg, with slightly more efficient cells then I used in my estimates.  (no votes) Tags: technology, planet earth.
	posted on 2007-08-01 18:31:00 | Report abuse

Reply	Theran says: The energy needed to keep the sattelite in orbit would be equal to the energy produced... unless you're Steorn that is.  (no votes) Tags: technology, planet earth.
	posted on 2007-08-01 19:36:00 | Report abuse

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