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So just had an idea that could work but would require billions to build:

Theoretically we could build a giant highway for satellites to orbit on but as they are orbiting they generate energy as they are on a treadmill which generates energy from the satellites movement. Would this work if it were built if so doesn't this beat the law of conservation of energy.

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    $\begingroup$ The answer to the question in the title is yes (obviously, satellites in orbit do produce and use electricity), and the answer to the question in the body is no, or at least not for very long. Please edit to make the title of your question match the actual question. If it helps, your model is closest in concept to an orbital ring (that I can think of). $\endgroup$ – TildalWave Jan 8 '16 at 2:11
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No, it wouldn't work.

In order to drive the treadmill, momentum would have to be transferred from the satellites to the treadmill. The sats would slow down and eventually stop.

The "highway" itself wouldn't be stable, either. Since it's moving at a different speed from the satellites, it cannot be moving at circular orbital speed for its altitude by definition; any tiny nudge on it will cause it to drift into the atmosphere and break apart.

As a general rule, if you think you have a scheme for free energy, assume the answer is "no" and then figure out why it's "no".

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    $\begingroup$ I'd give you a +1 for that last sentence alone. The rest of the answer just adds to its value. $\endgroup$ – a CVn Jan 8 '16 at 8:51
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Apart from the impossibility of harvesting energy, here's another way to sanity-check your grand designs.

A highway all the way around Earth would be a structure at least 40,000 km long. Let's optimistically say you can build such a highway by launching it in sections 100 m long each. That means 400,000 launches to create the highway.

We have only launched 6,600 satellites to date, and they're in all kinds of different orbits. The most densely-populated orbit is the geostationary orbit, with about 300 satellites.

The amount of energy put into 1 satellite is exactly 1 rocket launch. You can never recover more energy than what was put in. So in geostationary orbit, you can harvest at most 300 launches worth of energy. For an energy cost of 400,000 launches.

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