A while back I calculated the peak power requirements for a rotating space elevator. This system consists of an orbiting hub, rotating end-over-end, while an extended tether thousands of kilometers in length would dip into the atmosphere and grab a 50-tonne payload from a high-flying C17 Cargo Transport aircraft. The payload would be lofted to 12,000 km orbit with a circularization burn of just a few hundred km/sec.

The hub would naturally exchange orbital energy with the payload, and lose altitude while the payload gained. If the hub is to maintain its orbit, it must use nuclear-powered electrodynamic station-keeping engines to repel the earth's magnetic field. The power requirements would be approximately 4 gigawatts, working at 100 percent efficiency. To put this orbiting nuclear power plant in perspective, it can be compared with the Diablo Canyon nuclear station, shown below; notice the 5-story tall office building next to the reactors....

Reactor One output = 1.086 gigawatts
Reactor Two output = 1.119 gigawatts