To me it seems that the greatest obstacle to space colonization would be maintenance and production of materials and technology needed to sustain and expand the

To me it seems that the greatest obstacle to space colonization would be maintenance and production of materials and technology needed to sustain and expand the colony. Zubrin's estimate of this in The Case For Mars is a half million people. That's an estimate for the minimum size of the population which can support the knowledge base required to make everything to sustain a modern industrialized civilization. You'd need extremely small scale factories that can build everything needed for a modern civilization. It's been demonstrated that a single person can build up the infrastructure of an 1800's colonial village all by himself, up to and including a blacksmith's shop. That guy from Turtle Island Preserve could do it, dropped into a forest with a single knife. There's a YouTuber who does all that sort of stuff without the knife to begin with. It will be harder to do such bootstrapping on Mars, of course. I'm not sure that the half million estimate above included chip fabs. I somehow doubt it.