Yes, a thousand of them indeed. The asteroid belt, and Near Earth Asteroids. I don't mean living on them like the little prince:
That's not very practical without an atmosphere.
Nor living inside them as some suggest.
But rather, using the materials from the asteroid belt and first, from Near Earth Asteroids, to build Stanford Torus type habitats (for instance).
Fly through of the Stanford Torus design. There are many other suggested ways of making habitats in space. This was one of the first.
There's enough material there for a thousand Earths - a thousand times the total land area of Earth that is - complete with space to build buildings on top, forests etc.. It's quite surprising. That's the calculation that lead to the Stanford Torus designs and the ideas of O'Neil colonies etc. in the 1970s. By far the largest habitable area in the inner solar system inside of Jupiter.
CONFLICT FREE
And - there is no conflict with anyone else. There may well be asteroids we want to preserve. Ceres and Vesta for instance. But there are so many asteroids, and many of them are probably of little interest. Some may even be on a far future collision course with the Earth or some other planet when you start mining them for materials to build your habitat. Or even near future.
There is no problem of planetary protection, either of Earth or of Mars or anywhere else, if you choose carefully (there may be an issue with Ceres again, there's thought to be a remote chance of life there, perhaps a subsurface ocean, even possibly cryovolcanism - until we explore it better).
And your habitat will be much easier to build in some ways. If you want to move things around in space - you just need to apply delta v once. No need to truck it over long distances. Then again when you want to stop it.
Once the skeleton of your habitat is ready and up and ready to be set spinning, you then have the choice of building in whatever level of gravity you spin it up to, or in zero g.
You have sunlight available 24/7 and can design it to any climate you like, tropics if you like, or a cooler climate if you prefer.
And you can build it close to Earth, the first ones, making trade and resupply much easier.
IS THERE A FUTURE IN SPACE COLONIZATION?
I don't actually think myself that there is a huge future in space colonization done for its own sake, in the near future. Because however well these habitats work out, they can never be as easy to build as a habitat on Earth even in the worst places to live here such as the Arctic, Siberia, middle of Sahara desert, or even a Cloud Nine city floating high in the atmosphere. All of those would be much simpler engineering challenges than any kind of space settlement anywhere, seems to me, and easier to maintain and to make profitable.
But for those who think there is a future in space colonization, I'd have thought that space habitats using materials from the asteroid belt were the best bet, far better than Mars.
The Moon could be another alternative because it is so close to Earth and has natural caves useful for shelter. Then it has the peaks of eternal light at the poles, ideal for solar power and growing crops, and next to them ice deposits in the craters of night.
I can see them working on a more limited scale than colonization as settlements. Larger and larger eventually maybe into the thousands and the tens of thousands even of Stanford Torus habitats - so long as there is some reason for them being there. Such as space mining, tourism, exploration, scientific study, solar power for Earth. You can easily have an expensive hard to build settlement if it is supported by the Earth with a million to one ratio between the people on Earth supporting it, and the number of people living in the habitat. So long as you can find some reason for them to support you. So this could be possible long before it becomes possible to make them self sustaining, if that can be done at all.
For more about all this including other designs for space habitats along similar lines, see also my Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
ANOTHER - AND SURPRISING - SUGGESTION, VENUS CLOUD COLONIES
Then another place where humans could live, potentially, is in the cloud tops of Venus. It's a bit of a surprising habitat, but it has many advantages over Mars. Though I think rather highlights how difficult it is to live elsewhere than the ease of living in the Venus cloud tops. It's a lot easier than Mars I think, but not nearly as easy as anywhere on Earth.
But it does have many advantages for early colonies - except - that I can't think of any particularly good reason for being there, except to study Venus, which can probably be done almost as easily from orbit around Venus or Earth at this stage. If you wanted to do close up study of the Venus clouds, it could be a good place for a settlement.
It would surely be far easier to build a Buckminster Fuller type Cloud Nine colony here in the Earth atmosphere than a Venus cloud colony, because the Earth air is breathable. This is a one kilometer diameter spherical city, made like a Buckminster fuller dome, so far stronger than you'd expect yet very light. Could withstand everything the weather throws at it. And at that size, just the few degrees increase in temperature of a city over its surroundings would be enough to keep it floating in the air.
Project for Floating Cloud Structures (Cloud Nine), by Fuller and Shoji Sadao 1962. In practice they would probably be tethered to the ground with cables.Venusian cloud cities are similar - except that the Earth atmosphere is naturally buoyant on Venus with no need to heat it up even by one degree to stay buoyant, and no mountains you could collide with.
In the case of Venus they can be much smaller and still viable, because in the denser CO2 atmosphere, nitrogen and oxygen are lifting gases, about half the lifting power of Helium in our atmosphere.
So you get big spacious habitats, and it just so happens that the cloud tops of Venus are at exactly the right temperature and pressure for humans. And just above the clouds, perhaps going in and out of them, you actually have direct sunlight. Yet protected from cosmic radiation and solar storms by the thickness of the Venus atmosphere above you, equivalent, as on Earth, to ten meters thickneses of water.
And at that level in the atmosphere, the entire atmosphere rotates around Venus once every four days. So you have a reasonable day length too. Probably plants could do with artificial lighting at night simulating more of a 24 hour cycle, would have to see how it worked out. And no global dust storms to shut out most of the light of the sun for weeks on end.
The main disadvantage compared to a space habitat is the sulfuric acid in the clouds. But that's also an asset too as a source for sulfur and water, both useful to life. There's almost everything needed for life in the atmosphere, nitrogen also, carbon obviously and oxygen from the CO2. Only trace elements are lacking. And at full Earth pressure, not needed to be extracted from a near vacuum as on Mars.
And we know how to protect from sulfuric acid, even concentrated sulfuric acid, in acid manufacturing facilities. It's much easier and lower tech to make an acid resistant suit and covering for your habitat than it is to engineeer a pressurized spacesuit to hold in Earth pressure atmosphere against a vacuum, at ten tons per square meter outwards pressure.
ADVANTAGES OF VENUS UPPER ATMOSPHERE
First, it's the most pleasant place for humans to live outside of Earth. Depends, if you suffer from agraphobia you may prefer living in tunnels, and the idea of wide vistas over the cloud scapes and spacious light filled habitats may not appeal to you., and you may prefer living in a Lunar cave. I've talked about this idea to some who think that way. But many like to live in spacious light filled habitats with wide vistas.
It is very different from the surface of Venus - hot, high pressure, no way humans could survive there without massive help from technology. But at the cloud tops - then it is just the right temperature and pressure for us. Just the sulfuric acid to protect against. If you breached your acid resistant suit - well you've got a lot better chance of survival than if you damage your spacesuit which is the only thing that keeps out the vacuum in other situations.
The biggest advantages are the ultra lightweight construction, as there is equal pressure inside and out, even with tears in the fabric, the air would not rush out or the Venus atmosphere rush in, because the pressure is the same inside and out.
Then, the ability to work outside the habitat with just acid resistant suits and air supply, without the pressure differences that make spacesuits so awkward to use, and the low level of technology required to maintain habitats or even build new ones.
You could literally build space habitats out of wood and plastics as the main construction materials - and using plants that were grown mainly using materials sourced from the atmosphere itself. There is nowhere else in space where habitats would be so lightweight and so easy to build and maintain and support so many people for so little effort (comparatively) though not nearly as easy as on Earth.
The Russians were first to promote this in the 1970s. And though it is rarely discusssed, it is still a viable option I think. At least as viable as Mars.
Much lower tech than Mars.
Less by way of planetary protection issues.
Though there may be some issues as there is a perhaps remote possibility of life in the Venus clouds, which would survive due to the 30 days it takes for particles to fall through the habitable region of the clouds - an updraft would bring microbes back to the cloud tops to repeat the cycle. Not originated there, but originated on the surface when Venus was more habitable in the early solar system. There are indications of this as a possibility including particles that are non spherical in the clouds, just the right size to be microbes.
On forward and back contamination issues for Venus
BUT WHY WOULD ANYONE WANT TO LIVE IN THESE PLACES LONG TERM?
As with humans on Mars it's a bit difficult to think of a reason why people would want to live in any of these places long term if the idea is just to colonize them, with no other motive for being there.
Why anyone would set up home in such a difficult place with such challenges when they could much more easily set up even a floating city in the Earth atmosphere?
To make it as exact an analogy as possible, I'm talking here about a self sustaining floating sea city that grows all its own food, not supported by fishing or anything like that - and takes nothing from the sea except the water, salts, metals mined from sea water, and uses the atmosphere for oxygen to breath (so saving a lot on the complexity of a space habitat), nitrogen, carbon etc. And vents waste gases such as the methane and hydrogen sulfide that builds up in a human habitat.
If you can build a self sufficient space habitat, anywhere in space, you can most certainly build a self sufficient sea city housing far more people for much less cost.
The Seasteading Institute | Opening humanity's next frontier
That would be something that has minimal impact on the Earth, sustainable, much less mass than space habitats (because no shielding needed from cosmic radiation or to hold in the atmosphere, ten tons per square meter against the vacuum of space).
And no need to launch dozens of rockets to build it. It's surely a more ecofriendly solution at least in the near term.
Never mind simpler projects such as Seawater greenhouse in the deserts. Those are even simpler. Pipes in salt water from the sea, the hot desert sun evaporates it, leaving salt as a valuable byproduct and provides water to irrigate the desert - without depleting water tables, indeed adds to them. Reverses desertification. Many of the world's deserts are close to the sea.
By Raffa be - Own work, CC BY 3.0,SG phase II
There's a fullscale working seawater greenhouse in Australia. And there are ideas for using them on a much larger scale to reverse desertification, bring water to deserts, and grow food in deserts.
Seawater Greenhouse | About us
So, I find it a little hard to see space colonies working as a way of colonization. Not as an affordable way to feed and house people.
I don't see it being done as a backup myself either, because the idea just doesn't work too well if you examine it closely. There is no disaster that could make Earth so uninhabitable that the best place to live is Mars, Venus, or the space colonies.
There is no disaster anyone has suggested that would make Earth anything like as uninhabitable as any of these places I've mentioned, even the Venus cloud tops.
The only disaster that comes close is impact by a giant meteorite - but we can see from the cratering record ,that there has been no impact that large in the inner solar system for well over 3 billion years on Mars, Mercury, our Moon, moons of Mars, or what we have of the history of Venus' surface since its most recent global volcanic resurfacing. And models give the likely explanation - that we are protected from asteroids and comets from the outer solar system by Jupiter. Large comets get broken by tidal effects, hit Jupiter, ejected from solar system or hit the sun, and have to do repeated flybys of Jupiter to get into an orbit in the same plane and able to hit Earth. And the larger asteroids in the asteroid belt are in orbits that are stable on the hundreds of millions of years timescale.
Many humans would survive a CP boundary type impact - the dinosaurs went extinct, but turtles, crocodiiles and aligators, birds, the dawn sequoia tree, small mammals all survived. Delicate frogs in a tropical amazonian rainforest would go extinct. Many species would. But humans can survive anywhere from the tropics to the Arctic with just the most basic of technology - so some of us certainly would survive a giant asteroid impact.
So unless we do it deliberately; someone deflects a big asteroid from the asteroid belt to hit Earth, we are not going to go extinct from asteroids.
And what's more we can also detect asteroids - detect them many decades in advance with modest levels of funding compared with colonization attempts (half a billion dollars gets you a space telescope to find most of even the small ones within less than a decade) - and deflect them easily also given a long enough lead time (with enough lead time you only need centimeters per second delta v to add up to the radius of the Earth after a decade, or if it does at least one flyby of Earth first, the delta v needed may be so small you have to measure it in microns per second). Why not put all that effort into that project instead of trying to escape Earth if you are worried about asteroids?
So - rather than attempt to build a backup in space, for a disaster that can never happen, and with Earth s the best place to be to survive any disaster that can hit our solar system - we need to use our space resources to protect the Earth. To find those asteroids decades in advance which then makes it easy to deflect them.
With one decade of warning, you can move an asteroid by the radius of the Earth with a delta v of only cms per second. If you have a flyby of Earth in between (or anywhere else indeed) then you will get a "keyhole" it has to pass through so then you just have to miss that keyhole maybe hundreds of meters in diameter. In that case the delta v, if applied a decade before it needs to miss the keyhole, is only microns per second.
See: Giant Asteroid Headed Your Way? - How We Can Detect And Deflect Them
and: Why We Can't "Backup Earth" On Mars, The Moon, Or Anywhere Else In Our Solar System
UNTIL SUCH MEGAPROJECTS GET SO EASY THAT WE BUILD CLOUD CITIES ON EARTH...
Nobody has yet built that cloud nine city. We know how to do it and have the technology to do it, and I dare say some people would enjoy living in a cloud city - but we don't have a sufficient reason to do it.
It's like that with most of the space colonization ideas.
A Stanford Torus for instance or a giant space city dome, is technically feasible - but like Buckminster Fuller's cloud cities (which he never suggested as a thing we should actually do) - it can be a little hard to see why one would build them.
Until building mega structures is so easy for us that we have floating cities in our own skies, I doubt if we will have habitats in either Venus atmosphere, or on Mars or in outer space either - at last not just as places to live.
But if there is some other reason to be in these places, such as space mining, or science research settlements or whatever, then this may be how it is done.
REASON FOR BEING IN SPACE IN FAIRLY LARGE NUMBERS, THOUSANDS OF PEOPLE
And there again I think the asteroids score over the other habitats - the asteroids and the Moon. Because though we don't have the technology quite yet, we may in near future reach the point where it actually makes economic sense to have some people living there.
The Stanford Torus design assumed only 1970s technology, so technologically we can probably do it given the funding - of course may well be many issues to solve, not least, whether it is really possible to set up a closed system habitat that large, or mainly closed system. Also actual experience of the engineering challenges, and how easy it is to maintain etc.
But we'd need a reason for them to be there. For the Stanford Torus the reason was to build solar power satellites which they projected would have paid back its cost already by now several times by sale of low price solar power to the world.
It shows the kind of thing you need. You would of course start by mining the NEOs and the Moon, as the easiest places to get to from Earth, also easiest places from which to export back to Earth or to Earth originated spacecraft, satellites and space stations.
ADVANTAGES OF MINING IN SPACE
There are some ideas for mining that would work only in zero g and mining asteroids. For one thing it is easier to transport things - because in space you just need to apply delta v, let go, and it will reach the destination eventually so long as it is on a suitable trajectory - you don't need haulage along roads or tracks.
With a spinning asteroid you can also use an attached tether to convert that spin into delta v to send your exports back to Earth. It's like the idea of the space elevator - but much easier for an asteroid than for the Earth - it's also possible for the Moon too - though it spins much more slowly than the Earth, the gravity is also less making a tether practical with current engineering though something of a mega engineering project. But it is easiest of all for asteroids.
Then, the unique thing about asteroids is that some of them contain pure metal, hundred percent.
It's mostly iron and nickel, also rarer platinum, gold, silver, etc,. And there's a manufacturing process we could use in space that is not possible on Earth because these metals are in such pure form, not as oxides or any such.
The idea is to use carbon monoxide to convert them to metal carbonyls. Nickel particularly can be converted to Nickel Carbonyl, a gas, at 50 to 60 °C. It's the Mond process except you can miss out the first step of heating Nickel with Syngas to 200 °C because it is already the pure metal.
This suggests enclosing the asteroid in a bag, transparent and heated by the sun, and filling it with carbon monoxide. The result would be Nickel Carbonyl gas. This leaves all the impurities and other metals behind - and also - means you don't need to do any mechanical mining of the asteroid, a big bonus in space. Then to extract the nickel you have to heat it to 220–250 °C - this can be done using a 3D printer attached to the bag so you actually get printed Nickel parts as a result of the process, if you so desire.
Then to get the nickel back to Earth you use Ballutes - self inflating parachute / balloon hybrids, low weight, so ideal for an application like this.
Other metals could then be extracted from what remains of the asteroid using the same process at higher temperatures.
This approach has been suggested several times in the literature.
NEED FOR AN ECONOMIC REASON TO BE THERE
Now whether this is actually going to be economic in space I don't know. But if it did work it's an example of something that might make it worthwhile to have humans in space in fairly large numbers. Though on the other hand it might just mean lots of telerobots and semi-autonomous robots operated from the ground.
The original Stanford Torus design was based on the assumption that ten thousand people would need to be in space to build solar power satellites to beam energy back to Earth.
With modern ideas for doing this, you'd use thin film mirrors to focus the solar power, beam it back with microwaves, and maybe use high efficiency solar panels or solar furnaces. I'm not sure if this would need thousands of people in space any more.
The other thing is that you could supply water and ice and split water into hydrogen and oxygen as fuel and supply it to other spacecraft and habitats, research settlements, tourists etc. Again I can see this being a reason to have a few hundred people in space, not sure it needs thousands of them, will have to see how it develops.
But that's what you'd need, some economic reason for them being there. And also some reason why humans are better than robots or telerobots doing the same job in space.
And though that's hard to see anywhere in space right now, again seems most likely in asteroid belt or on the Moon.
Otherwise, who could afford a home in space, apart from the very wealthy, building a house in space much as they would buy a luxury cruiser or a private jet? And of course tourist resorts / hotels - and surely settlements for scientific research as we have in Antarctica.
I can see all of those happening. But as for colonization - why would anyone choose to build a home in space where it is so much more expensive to live than on Earth?
That is, until building big megastructures is so easy for us that we have cities floating on the sea, large Buckminster fuller domes in the sky - and then maybe space settlements in space as well. For that to work they would need to be not only reasonably easy to build - but also reasonably maintenance free. If you have to rebuild your space habitat every few decades like MIR, or the ISS, then it's not very practical as a place to live. If it can continue for a thousand years with hardly any maintenance with a not too excessive startup cost - well - it could be very affordable. Whether that ever happens, we aren't there quite yet.
But I can see settlements in orbit or on the Moon. Including this rather charming idea of an ESA settlement on the Moon which they are quite keen on at present. It looks almost as if the clangers are about to step out :).
ESA idea of a lunar village on the Moon.
See also my: Human Spaceflight At "Coastline Hugging Phase" - Lunar Villages Not Interplanetary Voyages - Op. Ed.
This originated as my answer to Can you suggest a second Earth aside from Mars?
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