I've often seen the idea put forward that one way to execute a Mars mission would be to use the planet's natural resources (iron, etc) to manufacture what was needed to exist on the planet (in some cases, people also suggest manufacturing the fuel - if not the craft - needed to return to Earth).
My question is this: wouldn't the machinery, plants, etc needed to extract and refine these resources be forbiddingly massive? And when we speak of manufacturing homes, vehicles, etc., wouldn't the machines necessary to do this be massive as well?
I'm speaking here not so much in terms of indvidual machines, but rather the assemblage of machines and facilities to accomplish these tasks.
Surely I'm not the first to wonder this (I don't claim, as a layperson, to have found a silver bullet that kills this whole idea), but I must be missing something about the plan. Can someone help here?