It's absolutely not beyond our current level of technology. Unfortunately, there are not economic incentives yet.
Now, this(1) it's beyond our current level, but one can dream.
It's obvious to me that this is the most probable future and I would not be surprise if, at some point, most humanity is living in this kind of environment instead of planets.
I think it might be better to say that's not beyond our current level of scientific understanding (it doesn't require any exotic materials or new physics). However it's likely beyond our practical engineering capabilities.
Early spaceflight up through Apollo was done with an army of humans with slide rules and rivet guns. We did it because there was a political imperative to do so. A lot of new technology was developed as a result. But it ended up being unsustainable because it was too expensive.
I think the key to making O'Neill cylinders feasible will be large scale outer space resource mining and in-space manufacturing. Both will require advanced robotics and AI. We could throw a bunch of money into developing that ... or we could just wait for the technology to develop here on Earth and then apply it to space.
Likewise, as much as I'd like to see a Mars outpost in my lifetime, it would be a lot cheaper and safer if we didn't rush it. Maybe by 2075 we'll have cured cancer and radiation won't be an issue, and we'll have self-repairing life support systems and one of those automated medical pods from the Alien movies.
There can't be an economic incentive, only political ones.
Much like pilgrims who founded Massachusetts, founders of space habitats will be groups of people who don't enjoy living on Earth badly enough (due to persecution, or because of desire of some grand reforms) to fund a move elsewhere.
I bet the first Martian colony will quickly be recognized as a place not controllable by any Earth government, and that will be a huge selling point for tickets to Mars.
I would imagine that any colony would be dependent on Earth (for survival) for quite a while. I think that it would take a certain level of self-sufficiency in order to reach a point of not being controllable by earth.
Being far away is one thing, but when I look at how powers on Earth exert influence and control over others, it seems you also need to be self-sufficient (protection from blockades, trade embargoes, or other modern "seiges"), and also sufficiently defended/defensible to avoid military threats. Sure, your Martian buildings may be underground, but would they be safe from heavy objects flung at them at high velocity? Seems like it would be easy enough for Earth to "put down" any Martian activities that rubbed people the wrong way for the foreseeable future.
It may be a bit more like the Triangle Trades of old [0].
Raw/rare materials and elements are mined in the Belt and are then sent to Earth for use in manufacture. You pick up the high quality goods and tools from Earth and ship them to Mars/Moon. Since there is water on Mars/Moon, you grow food, 'wet' supplies, and unfinished goods in the weaker gravity well for shipment to the Belt. These arrive in the Belt and you repeat the process, profiting at every spaceport.
As the metropole has overwhelming manpower/firepower due to it's high class manufacturing base and population, the threat of violence is just plain bad for business all around and is discouraged.
Now I'm gong to speculate very hard: Eventually, the lesser manufacturing base (Moon/Mars) will gain in economic and political power as their frontier life becomes more civilized and independent of the metropole. And they may try to declare independence fully. However, in the case of Moon/Mars, you're looking at a fully independent multi-generational extraterrestrial biospheres at that point and probably millions of people, if not 10s of millions, to run the whole thing. Lots of people that have never been to Earth and never plan on going. I really don't see that much trade/mining would be needed to go to Earth to build up and support permanently independent biospheres of a few generations of native Martians/Moonies.
There are no known commodity items that can be profitably mined in space.[0]
There will almost certainly be stuff like gold and rare metals shipped from a Mars colony to Earth, but only because returning the ships from Mars makes vital resupply easier. From a total system perspective it'd be better to keep the ship on Mars and scavenge it, but Mars will be on such an economic imbalance that they will want to make it easy as possible for Earth to resupply them. And if you're going to return the ships anyways, you might as well put something in them.
The diagram at the top of [1] is a good illustration of import vs make in situ vs export.
There are hundreds of asteroids that have more wealth than the entire US federal debt.
Consider all the precious metals ever mined on the planet. Now consider this is litterally scratching the surface of the total contained within the planet. Note, these dense metals will be concentrated toward the planets core, due to gravity.
The asteroid belt easily holds our planet's mass, but it is all spread thinly and relatively easy to access.
I don't think the mass is as important as accessible mass - let's say you can mine up to 4 km deep (the deepest mine on Earth at the moment) & you can't easily do that any, there might be ocean, glacier, or even a city on top of the resource you want to mine. That limits you even further for terrestrial mining.
Asteroid on the other hand are mostly just a few kilometers in size with a very few being bigger than tens of kilometers. That might quite possibly open much bigger mining volume than what's currently avalable on earth - rather than a big sphere with much stuff inaccessible due to being too deep, you now have millions of chunks floating around with a lot of stuff to dig through in the 4 km limit.
No oceans, cities or glaciers to block you as well.
And the arbitrary 4 km limit most likely does not really apply for asteroids - they are all long cooled down & the gravity is negligible
so nothing should really limmmit you from digging hundreds of kilometers through Vesta looking for valuables. Also some findings indicate that processes that lead to dilution of minerals on earth might have taken place after asteroids formed, so it might be possible to find the stuff we look for in quite a pure and ready to use state.
Well, it should enable many things that are currently prohibitively expensive due to the cost of materials.
You know, people don't buy stuff (just) because it looks nice and shiny but to use to to do things. Aluminium used to be more expensive than platinum yet we survived it's price tanking & it made practical airplanes and drink cans possible!
Ideally you would use it for building up space infrastructure primarily. You might still ship some finished products back to Earth, that would be much more mass efficient.
BTW, once you can have your payload trajectory intersect with Earth, you will get braking for free thanks to the atmosphere, effectively shaving half of the needed delta-v. Same thing on Mars.
Has anyone demonstrated manufacturing non-trivial centrifuges in space yet? Or mining and refining in space, given we can’t possibly afford to launch that much mass from the ground? Or fully modelled the lifecycle of that sort of megastructure to find out how, why, and when the chemistry of the occupants/internal farms/etc. causes fatal problems?
I’m eager to live in one of these, but I don’t think we actually know enough to build one at all yet, never mind safely.
Yeah - I'm a bit alarmed on how many people can't think out of the blue ball (sorry for the pun) - there are many many ways we can build our own environments as needed about anywhere in space given some resources and energy.
Also while Earth is pretty ideal, it is not perfect - for example some places in Japan can be regularly hit by earthquakes, tsunami, flooding, Typhoons and even volcanic eruptions!
If done right, habitats could be much better than planetary environments.
Obviously this is far beyond our current level of technology, though.