Following scenario: 1) Send a few rockets with large payloads to the moon, carrying various parts of a nuclear reactor to be assembled on the moon 2) Use the nuclear reactor to extract oxygen from various materials found on the moon 3) Use the power of the reactor to harvest resources for building more infrastructure Why hasn't it been done already? Which of those steps is beyond our means? It seems that it would be the most reasonable step to do, before any other steps when considering to further space exploration. Without any atmosphere and with only a fraction of the gravity earth has, one could easily build spaceships with materials on the moon and then use a mass driver to get them into orbit. So what exactly stopped us for so many years?