[narby]

Sounds like a cool idea. But what I don't understand is where the energy is coming from. If you boost a spacecraft higher, you must use energy, and that will reduce the energy in the tether.

I understand that you could recover the energy by taking higher spacecraft and lowering them, or de-orbiting them. But how often will this be done?

Maybe I'm answering my own question. The energy will be taken from dead spacecraft and boosters, with a side bennefit of cleaning up orbital space?

Might work, but sounds pretty complicated to organize.

[Frank_Discussion]

If I recall how it works, the tether harnesses the electrical energy produced by spinning the tether through the tenuous (but still significant) atmosphere of orbital space. This produces electricity through a dynamo effect, and this electricity is converted into propulsion.

One of tether experiments on the shuttle failed partly due to a current spike from more-than-anticipated electrical loads. It is an interesting technology, to say the least.

[RightWhale]

At some point they will run out of mass to balance. This isn't a perpetual motion machine: the clockworks will run down, but there might be ways to wind up the clock without burning chemical fuel.

[r9etb]

I understand that you could recover the energy by taking higher spacecraft and lowering them, or de-orbiting them. But how often will this be done?

You could raise the tether's orbit by pumping current through it. The tether would be just like the rotor in an electric motor, interacting with the Earth's magnetic field. Pump current, the tether moves.