In a far distant future, our descendants have lost the desire or the capacity to go into space, since Earth has had all its problems fixed and is now a near lotus-eating utopia. Global warming was fixed by the satellite armada, and global population growth has ceased. Earth is coming back into balance, and there are the usual squabbles between greenies and technoes about how fast it should be returned to nature, and what would be a stable world population.

Then, the next ice age begins, and someone finds out that we've lost the control codes for the satellite armada. If only they could be reprogrammed, then the ice age can be staved off.

But the codes can only be accessed from the main control station at L1...