Could cables in space generate electricity from Earth's magnetic field?
I've watched astronauts go to lots of trouble trying to install solar panels onto space stations. Why haven't they been clever and hung a few cables from the space station and let them generate electricity by letting them move across the Earth's magnetic field? Normally a generator works by moving a magnet through a magnetic field. This would be far less expensive than solar panels, so why don't they do it?
You can and they have tried it. They took a big long wire a couple of kilometres long and hung it from a shuttle. They tried to generate power by moving it through the Earth's magnetic field. The problem is that it's very difficult to manoeuvre a 2-kilometre wire through space. If you started a wave through it, there's no air to dampen down the vibrations. You also get some complex interactions between the magnetic field and the wire. The other problem is that it takes the energy out of the orbit, so the satellite will come out of orbit quicker. This is ok for a space station because it gets pushed regularly, but it's not ideal for a satellite that wants to stay up there for a long time. So actually it's a lot easier to use a solar panel.