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 materials from the asteroid belt and first, from the close Near Earth Asteroids, to build large habitats following the Stanford Torus design and others.
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 times the total land area of Earth - 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 an so forth. in the 1970s. This is 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. 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 in the near future. So by building your habitats you may simultaneously be preventing a future collision with Earth.
Also, for most of them, there is no problem of planetary protection, either. There is no chance of harm to Earth or Mars or anywhere else, if you choose carefully. You need to take care with some of the larger asteroids such as Ceres, with a remote chance of life there, perhaps a subsurface ocean, even possibly cryovolcanism. With asteroids like that, it's a case of exploring first with robots and telerobots until you know what you are dealing with.
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 to start it moving, then again when you want to stop it. There's no need to truck anything over long distances.
Once the skeleton of your habitat is up and ready to be set spinning, you then have the choice of building the rest of it in whatever level of gravity you spin it up to, or in zero g, as you prefer.
You have sunlight available 24/7 and can design it to any climate you like, such as the tropics, 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, the middle of the Sahara desert, or even a Cloud Nine city floating high in the atmosphere. There are many much more hospitable places on Earth to colonize. All of those would be much simpler engineering challenges than any kind of space settlement anywhere, it seems to me, and far easier to maintain.
The Sahara desert spreads all the way across Africa. It's vast and growing, as it extends further southward every year.
Sahara desert covers much of North Africa. It's 9.4 million square kilometres. Compare the 9.857 million square kilometers of the US, or the 9.597 million square kilometers of China.
If this could be made habitable, then you are talking about opening a whole "new world" to colonization, as vast as the United States. And helping many people who are in trouble at the moment because of the encroaching desert. And there are many other large desert areas. There are some desert habitats that need to be preserved and are unique. But many of them are just the result of desertification - the Sahara desert is expanding every year, to the extent that the countries south of it are desperate to stop this expansion. They are trying to build a "green wall" of forest along the southern margin of the Sahara desert to stop its spread.
The Sahara desert is so much easier to colonize than anywhere in space.
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. It also 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 eternal night, amongst the coldest places in the inner solar system - also ideal places to build passively cooled infrared telescopes.
I can see settlements like that working. 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, or solar power for Earth.
You can easily have an expensive hard to build settlement if it is supported by the Earth with, perhaps a million to one ratio between the people on Earth supporting it, and the number of people living in the habitat. So this could be possible long before it becomes possible to make them self sustaining, if that can be done at all. So long as you can find some reason for Earth to support you.
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 it 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 reason for being there, except to study Venus, and that 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, however, 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 tensegrity sphere, and so far stronger than you'd expect from its size and low weight, yet very light. It 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 , which happens anyway,would be enough to keep it floating in the air.
With a one kilometer diameter city, with thousands of people and their possessions, you can work out that a one degree increase in temperature over its surroundings would be enough. It would float like a hot air balloon, open to the atmosphere, but trapping enough heat to keep it afloat.
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's 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.
And actually in 1980 there was a serious proposal to build one of these as a research platform. See Solar Thermal Aerostat Research Station (STARS) and the news story about it in the Washington Post: "Solar Powered Balloon Station Proposed For the Edge of Space".
An artist's impression of STARS, proposed "dyson sphere" type upper atmosphere research station. This is Peter Elson's "Orion Shall Rise" painting, an illustration from Poul Anderson's novel of the same name, Orion Shall Rise, which features the STARS aerostat.
(reproduced with permission, non commercial use only).
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, with about half the lifting power of Helium in our atmosphere.
So you get big spacious and lightweight habitats, constructed much like an airship on Earth. 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 you are protected from cosmic radiation and solar storms by the thickness of the Venus atmosphere above you, which equivalent, as on Earth, to ten meters thickness of water.
And at that level the entire atmosphere rotates around Venus once every four days, a bit like our jet streams. As with a hot air balloon, since you are carried with the wind, you wouldn't experience it as a wind. The air would be calm around you.
So you have a reasonable day length too. Probably plants could do with artificial lighting at night simulating more of a 24 hour cycle. You would have to see how it worked out. And unlike Mars, there are no global dust storms which shut out most of the light of the sun for weeks on end every two years.
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, the air around the habitat doesn't 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 covering for your habitat and acid resistant suits for working out of doors than it is to engineer a pressurized habitat and spacesuits to hold in Earth pressure atmosphere against a vacuum, at ten tons per square meter outwards pressure.
ADVANTAGES OF THE VENUS UPPER ATMOSPHERE
First, it's the most pleasant place for humans to live outside of Earth. It depends, if you suffer from agoraphobia you may prefer living in tunnels, and the idea of wide vistas over the cloudscapes and spacious light filled habitats may not appeal to you. If so, 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 - which is extremely hot, at a high pressure, and there is 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, and need for air to breath when out of doors. 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, it's a big advantage to be able to work outside the habitat with just acid resistant suits and air supply, without the pressure differences that make spacesuits so awkward to use. Also there's a much low level of technology required to maintain habitats or even build new ones.
You could literally build these aerostat habitats out of wood and plastics as the main construction materials, as they are easily strong enough. You could use plants 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 of course, it is not nearly as easy as on Earth.
The Russians were first to promote this in the 1970s.
And though it is rarely discussed, it is still a viable option I think. At least as viable as Mars.
NASA have explored the idea too, with their HAVOC internal study, an idea for a series of missions that would lead to a Venus colony
HAVOC project page - and see the Universe Today article, "Exploring Venus by Airship - Cool Concept but Certainly Not New"
It's also much lower tech than Mars. If we can make self sustaining habitats producing their own oxygen, using plants only, the rest is very low tech. And the way the photosynthesis calculations work, if they are able to grow their own food, then they automatically also produce more than enough oxygen for humans to breath. Of course that's the big question for space habitats, but it's the same for anywhere in space. See http://www.science20.com/robert_inventor/could_astronauts_in_the_iss_get...) ">Could Astronauts In The ISS Get All Their Oxygen&Food From Algae&Plants?
There's also less by way of planetary protection issues.
Though there may be some issues as there is a perhaps a 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. The idea there is that an updraft would bring microbes back to the cloud tops to repeat the cycle.
If there is life, it surely didn't evolve there, but originated on the surface when Venus was more habitable in the early solar system. There isn't much to go on yet, but we know that there are particles that are non spherical in the clouds, just the right size to be microbes. (Droplets of rain, fog, etc are usually spherical).
If there is life there, we would have to be careful just as we are with artificial lifeforms made in the laboratory, and should be with any life with possibly non terrestrial biology.
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, lunar caves, Venus aerostat habitats, or large free flying space habitats, 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's atmosphere? Or indeed, even easier, a sea city.
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. It 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), and also takes nitrogen, carbon etc from the atmosphere. And vents waste gases such as the methane and hydrogen sulfide that build up in a human habitat.
If you can build a self sufficient space habitat, or aerostat 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, and with much less mass than space habitats (because no shielding is needed from cosmic radiation, and no need to engineer it to hold in the atmosphere, at ten tons per square meter pressure, against the vacuum of space).
And there's 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 a Seawater greenhouse in the deserts. Those are even simpler. Pipes in salt water from the sea, then the hot desert sun evaporates it, leaving salt as a valuable byproduct and provides water to irrigate the desert. And it does that without depleting water tables; indeed adds to them. Reverses desertification. Many of the world's deserts are close to the sea, and would be ideal sites for this.
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, at least.
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 natural 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 impacts large enough to make humans extinct, in the inner solar system for well over 3 billion years. There are no recent craters that big 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 either 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, crocodiles and alligators, 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; and someone deflects a big asteroid from the asteroid belt to hit Earth, we are not going to go extinct from asteroids. Indeed space colonies, if done hastily sending millions into space, could end up with conflict in space or with the Earth, which might lead to the very events they are trying to prevent. After all humans haven't changed, and however idealistic the first colonists are, eventually you'd get the same range of opinions and attitudes, and the same tendencies towards aggression and warfare as you get on Earth.
And what's more we can also detect asteroids - detect them many decades in advance with modest levels of funding compared with colonization attempts.
With half a billion dollars gets you a space telescope to find most of even the smaller asteroids within less than a decade. You can't do much space colonization with half a billion dollars.
You can also deflect them easily given a long enough lead time. You only need centimeters per second or delta v to move an asteroid by the radius of the Earth after a decade. Then, once we have most of them mapped out, it's likely to do at least one flyby of Earth first. If so, the delta v needed may be so small you have to measure it in microns per second, in order to miss a few hundred meters diameter keyhole a decade into the future.
Why not put all this 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 as the best place to be to survive and rebuild - 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.
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 want to build them.
So, until building mega structures is so easy for us that we have floating cities in our own skies, I doubt if we will have large habitats in either the Venus atmosphere, or on Mars or in Mars orbit, 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, OF THE ORDER OF THOUSANDS OF PEOPLE
And there again I think the asteroids and the Moon score over the other habitat ideas. 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 it's probably well feasible for us if we had the funding. Of course there may well be many issues to solve which they didn't answer, not least, whether it is really possible to set up a closed system habitat that large, or a mainly closed system. Also it's bound to need to be modified through actual experience of the engineering challenges on the job, and how easy it is to maintain etc.
But we'd need a reason for them to be there. For the Stanford Torus in the 1970s, 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 reason you need. But this needs to be rethought for a new generation.
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 the materials as we saw, just need to apply delta v, let go, and it will reach the destination eventually so long as it is on a suitable trajectory.
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. See Extraterrestrial space elevators
Then, the unique thing about asteroids is that some of them contain 100% pure metal.
It's mostly iron and nickel, also with a fair amount of the rarer platinum, gold, silver, etc. Platinum especially is much more abundant in iron rich meteorites than on Earth. 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, which is 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.
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.
Then to get the metals back to Earth you can use Ballutes - self inflating parachute / balloon hybrids, low weight, so ideal for an application like this. For more about that idea, see Profitably Exploiting Near-Earth Object Resources
Or, a more recent idea, use this new inflatable heat shield called HIAD developed by NASA which may be available soon. It's already been tested and found to survive re-entry from space.
HIDA - Inflatable heat shield being developed by NASA to make it easier to land large payloads on Mars and on the Earth
Artist impression of it is used for an Earth re-entry. Images from this news story from NASA. For the 2012 test, which was successful, used for an actual re-entry from space, see Nasa's inflatable heat shield survives toughest test yet
Lightweight heat shields like this, together with use of ice from asteroids for fuel could be used to supply materials from asteroids to Earth.
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, rather like solar sails, to focus the solar power, and maybe use high efficiency solar panels or solar furnaces to convert to electricity which you then beam back to Earth safely using phased arrays of microwaves.
It still seems practical enough so that there's a fair bit of research done into it; however, 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 if it needs thousands of them, and we 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, or else you'll get a competitor doing the same job with them in stead..
And though that's hard to see anywhere in space right now, again, it seems most likely to start with Near Earth asteroids or on the Moon.
Otherwise, who could afford a home in space, apart from the very wealthy, buying 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
This originated as my answer to Can you suggest a second Earth aside from Mars?
See also my: Human Spaceflight At "Coastline Hugging Phase" - Lunar Villages Not Interplanetary Voyages - Op. Ed.
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