“Go on, Emily,” I suggested. But I couldn’t help listening with only half my attention. Pacifica was coming in, gear extended like a fighter landing on an aircraft carrier. I could hear the controllers talking softly in their singsongy dialect.

“Well, sir,” Emily said, almost without a trace of accent, “I wasn’t able to find a way to prevent the potential buildup. I’m afraid the voltage is unavoidable as the conductive tethers pass through the Earth’s magnetic field.

“In fact, if the charge had anywhere to go, we could see some pretty awesome currents: One deck might act as a cathode, emitting electrons into the ionosphere, and the other could be an anode, absorbing electrons from the surrounding plasma. It all depends on whether…”

Pacifica touched down with barely a bump. Her landing gear flexed slightly as she rolled to a stop. The interdeck elevator resumed its descent as the orbiter was tied down by the B Deck crew. Her cargo was removed from the open cargo bay by giant manipulator arms.

Two spacesuited figures drifted down from Pacifica’s hatch and stood waiting for the elevator. It didn’t take a lot of imagination to guess who they were. Our bad news boys.

Emily went on single-mindedly, apparently unaware of my split attention. “…so we could, if we ever really wanted to, use this potential difference the tethers generate! We could shunt it through some transformers here on A Deck, and apply as much as twenty thousand volts! I calculate we might pull more power out of the Earth’s magnetic field, just by orbiting through it with these long wires, than we would ever need to run lights, heat, utilities, and communications, even if we grew to ten times our present size!”