You would think that 3D printers would have solved the scarcity problem. In fact, the technology had just moved the bottleneck. We could build more drones to extract and haul the metal out of Earth’s gravity well, or we could build colony ships, or we could build more printers in order to produce more drones and colony ships during which time we would be producing neither. The calculations to determine the optimum path were finicky and had large error bars. Even thinking about them made me grit my teeth.