You aren't quite thinking large enough here :).
With resources from the asteroid belt, we could build Stanford Toruses or O'Neil cylinders large enough for a thousand times the surface area of the Earth.
Population into the trillions. This is a calculation that goes back to the 1970s. Far more potential for colonization in materials from asteroid belt, NEOs, moons etc than on planetary surfaces in our solar system.
The main mass is for cosmic radiation shielding. Our atmosphere provides ten tons per square meter of shielding. In an O'Neil Cylinder or Stanford Torus we can get by with about 4.5 tons per square meter. But turns out there is enough material in asteroid belt for that much shielding for land area of a thousand Earths.
As for atmosphere, then it's better to do a Stanford Torus than an O'Neil cylinder as it has less atmosphere - so that's probably the best way to go if you want the most habitable area - build lots of toruses rather than cylinders. There's enough material in the asteroid belt for this.
Then - the area here is the area of the "ground floor". You can build houses, cities, skyscrapers even, on top of this.
With some plans - then you might have many nested levels internally. If so then, as only the outermost layer of your habitat needs shielding, you could have not just a thousand times the land area of the Earth, but many thousands of times this total area using just material from the asteroid belt.
The one thing we can't duplicate from the asteroid belt are the Earth's oceans. There isn't enough water ice in the asteroid belt for a single Earth ocean. That would need materials from further afield, maybe from the Oort cloud.
However - can have shallow lakes, seas and rivers in the habitats.
And still using materials from asteroid belt - can have occasional habitats just for "mini ocean worlds" with small surface area but deep oceans kilometers deep, large enough for e.g. whales and giant squids to live in them (hard to make them strong enough - but perhaps spin them more slowly - if sea creatures don't need full Earth gravity).
A smaller habitat for 10,000 people could be constructed from a single NEO - or from materials dug from a tiny patch of the Moon by a small bulldozer working for a year or two and sending the materials into space via mass driver.
Nereus diameter 300 meters max, is irregular in shape, but has a volume of 0.019 cubic kilometers approximately. That's enough for 2.5 square kilometers of surface living area.
Your ten million people would need a thousand of these - so the shielding would use, e.g. the materials from an entire small asteroid two or three kms across.
I like living on the Earth with our climate, wild life etc.
Big question for a space colony would be - how easy is it to maintain?
Our space stations need to be replaced every few decades. If a Stanford Torus was like that - then it's not an easy place to live long term.
But if it can be made easy to maintain - last for centuries - or thousands of years with minimal maintenance - then could be quite similar to building houses on the Earth. Then inside of it you can build conventional houses not needing the massive constructions of space stations.
I think would be a congenial place to live. You can make it any climate you like inside, e.g. like the tropics. Space is so insulating - that the main issue is to find a way to radiate away the excess heat - if it is in the inner solar system reasonably close to Earth.
I think also that a closed system habitat is achievable in the not too distant future. Biosphere II got pretty close to achieving it - though it's not been followed up enough to confirm that it can be done. I think with enough research and effort we can make reasonably closed system large but not enormous habitats based on biology rather than machines.
But you'd need to be a totally peaceful civilization. If we were at all war like and you had a war e.g. between Earth and a Stanford Torus - or between different space settlements - then they would be highly vulnerable - like any space settlement - and would not last long. That's because they are totally dependent on artificial atmosphere, surrounded by vacuum, and have to be engineered to hold in atmosphere at tons per square meter outwards pressure.
So - I think before settling in such a place - I'd want our world to be a more peaceful place than it is now. If we continue as violent and war like as a species as we are now, and carry those tendencies into space - I can't see space settlements being safe places to live long term.
A Stanford Torus for instance could be destroyed by a single spaceship hitting it at the kilometers per second speeds of ordinary spaceflight between planets - easily achieved - and not classified as weapons even - if you can go into space and build these habitats - you'll have equipment able to send tons of material around the solar system at kilometers per second - and any of those could easily destroy a Stanford Torus if misdirected, deliberately or by accident.
Unless that is - that we can contain our violence to the Earth - and not have wars in space - that's another possibility - which maybe will be possible if we can develop following the peaceful requirements in the Outer Space Treaty, and explore space in a peaceful collaborative way between all the nations of the Earth.
Either that - or else - well we just won't succeed in establishing long term colonies in space - they will destroy each other or the Earth will destroy them at some point.
See Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
With resources from the asteroid belt, we could build Stanford Toruses or O'Neil cylinders large enough for a thousand times the surface area of the Earth.
Population into the trillions. This is a calculation that goes back to the 1970s. Far more potential for colonization in materials from asteroid belt, NEOs, moons etc than on planetary surfaces in our solar system.
The main mass is for cosmic radiation shielding. Our atmosphere provides ten tons per square meter of shielding. In an O'Neil Cylinder or Stanford Torus we can get by with about 4.5 tons per square meter. But turns out there is enough material in asteroid belt for that much shielding for land area of a thousand Earths.
As for atmosphere, then it's better to do a Stanford Torus than an O'Neil cylinder as it has less atmosphere - so that's probably the best way to go if you want the most habitable area - build lots of toruses rather than cylinders. There's enough material in the asteroid belt for this.
Then - the area here is the area of the "ground floor". You can build houses, cities, skyscrapers even, on top of this.
With some plans - then you might have many nested levels internally. If so then, as only the outermost layer of your habitat needs shielding, you could have not just a thousand times the land area of the Earth, but many thousands of times this total area using just material from the asteroid belt.
The one thing we can't duplicate from the asteroid belt are the Earth's oceans. There isn't enough water ice in the asteroid belt for a single Earth ocean. That would need materials from further afield, maybe from the Oort cloud.
However - can have shallow lakes, seas and rivers in the habitats.
And still using materials from asteroid belt - can have occasional habitats just for "mini ocean worlds" with small surface area but deep oceans kilometers deep, large enough for e.g. whales and giant squids to live in them (hard to make them strong enough - but perhaps spin them more slowly - if sea creatures don't need full Earth gravity).
A smaller habitat for 10,000 people could be constructed from a single NEO - or from materials dug from a tiny patch of the Moon by a small bulldozer working for a year or two and sending the materials into space via mass driver.
Nereus diameter 300 meters max, is irregular in shape, but has a volume of 0.019 cubic kilometers approximately. That's enough for 2.5 square kilometers of surface living area.
300 meter diameter NEO - large enough for cosmic radiation shielding for 2.5 square kilometers of surface living area in a Stanford Torus
Your ten million people would need a thousand of these - so the shielding would use, e.g. the materials from an entire small asteroid two or three kms across.
I like living on the Earth with our climate, wild life etc.
Big question for a space colony would be - how easy is it to maintain?
Our space stations need to be replaced every few decades. If a Stanford Torus was like that - then it's not an easy place to live long term.
But if it can be made easy to maintain - last for centuries - or thousands of years with minimal maintenance - then could be quite similar to building houses on the Earth. Then inside of it you can build conventional houses not needing the massive constructions of space stations.
I think would be a congenial place to live. You can make it any climate you like inside, e.g. like the tropics. Space is so insulating - that the main issue is to find a way to radiate away the excess heat - if it is in the inner solar system reasonably close to Earth.
I think also that a closed system habitat is achievable in the not too distant future. Biosphere II got pretty close to achieving it - though it's not been followed up enough to confirm that it can be done. I think with enough research and effort we can make reasonably closed system large but not enormous habitats based on biology rather than machines.
But you'd need to be a totally peaceful civilization. If we were at all war like and you had a war e.g. between Earth and a Stanford Torus - or between different space settlements - then they would be highly vulnerable - like any space settlement - and would not last long. That's because they are totally dependent on artificial atmosphere, surrounded by vacuum, and have to be engineered to hold in atmosphere at tons per square meter outwards pressure.
So - I think before settling in such a place - I'd want our world to be a more peaceful place than it is now. If we continue as violent and war like as a species as we are now, and carry those tendencies into space - I can't see space settlements being safe places to live long term.
A Stanford Torus for instance could be destroyed by a single spaceship hitting it at the kilometers per second speeds of ordinary spaceflight between planets - easily achieved - and not classified as weapons even - if you can go into space and build these habitats - you'll have equipment able to send tons of material around the solar system at kilometers per second - and any of those could easily destroy a Stanford Torus if misdirected, deliberately or by accident.
Unless that is - that we can contain our violence to the Earth - and not have wars in space - that's another possibility - which maybe will be possible if we can develop following the peaceful requirements in the Outer Space Treaty, and explore space in a peaceful collaborative way between all the nations of the Earth.
Either that - or else - well we just won't succeed in establishing long term colonies in space - they will destroy each other or the Earth will destroy them at some point.
See Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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