@SerbanTanasa You'll never boostrap colonization based on an economics argument unless some unobtainium is found that Earth can't live without (the justification for colonization in the movie "Avatar"). Once we find a habitable planet, you'll likely have everyone from scientists to persecuted religious minorities petitioning to live permanently on the planet. It's the space stations that you'll never find non-scientific justification for. Yes, some will do it because it's "cool" and possibly the...

@SerbanTanasa ...neutral-politics justification made in "Star Trek Beyond," (which opens the door to military reasons). But on straight economics? I don't believe it can be done.

@JBH I am not sure I buy that argument. At the very least, trivially small populations could be deployed on a semi-permanent basis for highly valuable high maintenance operations where telerobotics and automation are just not enough. Admittedly, that more describes an oil rig than anything else on Earth. Allow me to pursue the space station argument further though.

Why is it impossible that at some point bulk-constructing a habitat for say 100,000 people or 1,000,000 people would not result in cheaper housing in orbit than on the planet. The economies of scale might actually flip against Earth construction at some point.

Right now, the median price for a home in the United States is somewhere around USD $400,000. California has a median price per sq. ft. of $324> USD $300. So while getting space habitats to provide price-competitive homes would take a lot, I don't see anything about physics that says it is utterly impossible to provide a sq foot of living space on a habitat for <$300 + whatever price inflation occurs in housing between now and then.

@SerbanTanasa Trivially small populations means they're meaningless for the answer to your question. Energy doesn't reduce transport, construction, or maintenance costs - only operation costs. As Asimov once said, "a sufficiently advanced technology is indistinguishable from magic." You're describing magic. By that point in human history, your original question becomes irrelevant. Finally, you can always build down on a planet cheaper than you can push up into orbit. Whatever tech makes orbit...

@SerbanTanasa ...cheap also makes digging down cheap (technology never exists in a vacuum). I know you don't want to hear this, but while it might be advantageous to build in space, it'll never be cheaper. The bottom of a gravity well is always to point of lowest energy consumption. The energy expended to climb out of it needs to be worth it. (Unless we're talking about magic again, but again, at that point the question becomes moot).

@SerbanTanasa Finally, let's assume you ask your question from the perspective of, "assume all costs are irrelevant and that it's equally economical to build out into space as it is on Earth...." The answer I gave is again the only relevant answer. One colony can only equal Earth's population at best. Two colonies can exceed the population. How long it takes is a function of those equations so long as you ignore so many things that the question isn't relevant (like war, tech development, etc.)...

@SerbanTanasa ...Every colony beyond two just speeds up the process.

@SerbanTanasa Finally, keep in mind as you ponder space habitats (I've already mentioned this, but you're fixed on the cost of living space. That's short sighted.) that you must also pay for transportation of the people, of raw materials and food, transportation... transportation... If the cost per square foot was $0, I'd bet a milkshake it still wouldn't be cheaper. The cost of transporting milk 100 miles from a dairy to a city is nothing compared to moving it 22,000 miles into orbit.

I don't think I am describing magic at all -- I am just thinking that economies of scale, when the power supply cost is probably 1/1000th or 1/1000,000th of what it is on earth, will make megastructures possible. In space, building megastructures is relatively easier than on Earth, assuming you have the capability to put it up there (say a solar-powered big railgun on the moon)

In fact, I think once we figure out how to run an automated factory on the moon (this may be as little as 10 years away), and establish basic lunar launch capabilities to Earth GEO or Lagrange points, all the basic ingredients are in place.

@JBH regarding "bottom of a gravity well is always to point of lowest energy consumption" -- absolutely, unless the matter does not come UP the gravity well, as it wouldn't from for example, lunar mining. If you look at the delta-V budget, it's much cheaper to put things in Earth orbit from the moon than it is from Earth. Although, as we just discussed, if the space solar arrays are deployed in bulk, and if that bounty of power can be sent (microwaved?) to Earth, folks might not care...

@JBH "Energy doesn't reduce transport, construction, or maintenance costs - only operation costs." - Not sure what you mean -- energy IS the bulk of transport cost. You have depreciation and maintenance of the physical plant (car, rocket, shuttle) and the expenditure of gas/rocket fuel etc. Construction -- most of the cost is in transforming the atoms from one state to another -- mining, melting, casting etc --- the main cost there is also energy

@SerbanTanasa I'm sorry, SerbanTaasa, but you need more experience with the science behind what you're talking about. It's almost like you think the mythology behind Nokolai Tesla justifies near-future energy transmission. Microwaving energy back to earth would cook the earth. Energy doesn't focus very well, especially when everything constantly in motion. If your hopes come to fruition at all, it's 500-1000 years in the future, not 10-20. You're oversimplifying so much (and don't understand...

@SerbanTanasa that you're doing it) that it's hard to know where to start explaining why what you're describing is unrealistic. Energy is certainly a core issue when it comes to space travel and habitation, but it's far, far, far from being so significant that everything else can be ignored. Given today's solar panel efficiencies, a 100-mile-square solar panel array would be hard pressed to collect enough energy in a day to launch something into orbit. By the time what you're talking about exists...

@SerbanTanasa ...(if ever), we'll have built both up and down on the surface, making it that much harder to answer your original question. Megastructures are so inefficient that I personally consider them evidence of fools rather than advanced tech and never expect to see evidence of one in humanity's existence.

I understand that I am simplifying complex issues. Technical issues are hard. Before SpaceX started landing rockets, everybody would have said the idea of landing rockets is stupid. I think you underestimate exponential growth curves -- 1000 years ago, everything about today's world would have appeared as unthinkable magic. Nothing about what I'm talking about appears to me as unthinkably magic, just difficult given our current lack of a space-based industrial base.