Everyone in the base thought they were safe and snug, dug into the side of the ringwall mountain they had named Yeager. Sheltered by solid rock, they had little fear of the dangers up on the airless surface, where the crater floor was bathed in hard radiation and the temperature could swing four hundred degrees between daylight and night, between sunshine and shadow.

But Doug saw how terribly vulnerable they all were. They had protected themselves against the forces of nature, true enough. But now they were threatened with destruction by the hand of war.

Doug looked out at the solar farm, thousands of acres of dark solar cells that greedily drank in sunlight and converted it noiselessly into the electricity the base needed the way a man needs blood. They could be blown to dust by conventional explosives or blasted into uselessness by the radiation pulse from a nuclear warhead.

Even easier, he realized, an enemy could knock out the radiators and we’d all stew underground in our own waste heat until we either surrendered or collapsed from heat exhaustion.

His eyes travelled to the rocket pads. They were empty now that the morning’s lunar transfer vehicle had loaded up and departed. Beyond, he saw the geodesic dome that sheltered the construction pad; inside it, a half-built Clippership was being built by virus-sized nanomachines that converted meteoric carbon dust into the hard, strong structure of pure diamond. How could we protect spacecraft sitting out on the pads? We can’t shelter them and we don’t have the facilities to bring them underground. That dome is no protection against missiles or even bullets.

He looked farther out across the crater floor, to where the mass launcher stretched its lean dark metallic finger to the horizon. A single warhead could wreck it forever, Doug knew.