[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.

[Frank_Discussion]

See my previous post - I don't think it's all a case of momentum transfer.

[mvpel]

The way in which you boost the tether to a higher orbit is by using the earth's magnetic field and the tether itself as a sort of electric motor. By running solar electricity through the tether, you wind up with a magnetic force that will serve to push the tehter to a higher orbit.