> Concrete and glass might be virtually unlimited, but certain metals are definitely not. Automated asteroid mining basically takes care of that. Even the larg

> Concrete and glass might be virtually unlimited, but certain metals are definitely not. Automated asteroid mining basically takes care of that. Even the largest asteroids can be easily excavated right down to the core, and many of them contain a wide abundance of many metals, basically everything from Lithium to Copper to Nickel to Platinum or Iridium. With low gravity and 24/7 in situ solar power any reasonable separation technology can just be let loose and given time to work. Near Earth orbit there's more than 10 gigajoules of energy available per year per square meter from solar power, and that includes factoring in the efficiency of conversion.