This is more or less the same question as this one: Why are we thinking about a Mars colony when a Venus colony would be more technically feasible? It seems that radiation shielded floating colonies could be assembled on Venus, with plastic film and aluminum wire bags, filled with breathable air. so I've copied my answer over here. With a summary first:
I'd say that in many ways the Venus cloud tops are more habitable and would be easier to colonize, though neither is anything like as habitable as even the harshest deserts on the Earth. Yes we haven't colonized the atmosphere of the Earth, we don't have "Cloud nine" type habitats floating above our mountains. But we could do. We could also colonize deserts, or the sea floor, or have floating sea cities. All of these I think are far more habitable and easier to colonize than Mars, for less cost, and more sustainable.
Venus - I think may be between the two, not as easy as Earth but many advantages over Mars, when you think it through. But I don't think you'd go to either place if your main motivation is to find an easy place to build a house. In the entire solar system, surely the Earth is by far the obvious place to build homes for humans. Even on mountain tops, or in cloud cities or deserts, nothing else compares with Earth.
I'd argue the same way as Geoffrey Landis. Being able to build without need to engineer to contain multiple tons per square meter - and without need to add meters thickness of radiation shielding is a huge advantage.
If you want a one way mission, then Venus and to stay is better than Mars. Because also - you have the advantage of being able to land using a normal parachute as for Earth, can't do that on Mars. And delta v slightly less. And no hard surface to hit - so long as your habitat or hydrogen balloon opens out at some point around the right level during the slow descent by parachute - then you are fine. No need for fraction of a second precision landing maneuvers.
The lifting force on Venus is huge if you build big habitats - and - you can build them huge without much material. It's like an airship - but filled with ordinary atmosphere rather than helium, because the Earth's mainly nitrogen atmosphere is a lifting gas in the mainly CO2 atmosphere of Venus - and you can of course use hydrogen as a lifting gas as well - e.g. for smaller vehicles.
We have already sent balloons to the upper Venus atmosphere, Venera balloons from Russia. Russia actually had ideas for Venus cloud colonies back in 1970s
The sulfuric acid is not nearly as much as a disadvantage as suggested. After all we have sulfuric acid plants, and know how to build machinery to deal with sulfuric acid.
Only the exterior of the habitat - and of any suits or aircraft that need to go out into the atmosphere need to be protected.
As for the crushing heat if you fall -well if you fall on Mars and e.g. break the visor of your spacesuit - or tear it or some such - you will die in seconds from breach in your spacesuit because of the thin almost vacuum atmosphere.
If you fall in the Venus atmosphere - there is some time for rescue - and you can be tethered to the habitat etc. I'd say in terms of safety for humans outside of the habitat, that Venus wins hands down over Mars. Manly because your protection suit is much lower tech. Instead of a spacesuit, you just need protection from the sulfuric acid, and oxygen breathing equipment, and can equalize pressure inside and out.
As for hit by incoming spaceship - that's a major issue for any space colony. With the Venus ones - well if it is just some debris creating holes - remember that inside and out is at same pressure so won't explosively decompress no matter how many holes there are. Just gradual diffusion of the atmosphere. And an incoming spaceship will be floating in parachutes - or if not - would burn up in the atmosphere (while on Mars won't burn up so easily if it comes in fast). So again, Venus scores over Mars.
- this is the sort of building construction needed for any habitat on Mars able to have a liveable atmosphere for humans. Low pressure greenhouses for plants only don't need to be quite so engineered, but still far far stronger than Earth greenhouses, still of order of a ton or so outward pressure per square meter) - same for the Moon or anywhere in space:
But summits of Himalayas are some orders of magnitude easier places for humans to live than Mars surface. You wouldn't need to engineer to withstand tons per square meter outwards pressure or add meters of cosmic radiation shielding to cover your habitat, and could get oxygen from atmosphere no need to split it from water.
Also do have Buckminster Fuller's Cloud Nine (tensegrity sphere)
Never been built, but seems practical enough, if you work through the engineering details - I think that's generally agreed (though might surprise you if you haven't looked into it) just don't need them here enough to want to build one. A cloud nine in Venus atmosphere doesn't even need to be warmer than the surrounding air.
So have a road map to build entire cities in the Venus atmosphere in the future.
To start with - yes do need to send rockets there and have them float in the atmosphere next to the colony ready to return. Expensive but do-able - not sure it is enormously harder than sending a rocket to Mars able to return to Earth - needs someone with the brilliance of Robert Zubrin to work on the engineering details, I think they would find a solution.
Has one advantage - no need for careful touch down on a hard surface. Just need parachute to slow down - and then hydrogen balloon inflates when it is at the right level in the Venus atmosphere - and you have a rocket suspended in the atmosphere next to the habitat ready for return trip.
If you want to suspend a Falcon Heavy fully loaded for take off - that's a little under 5 times the mass, would need 775,175 m3, so need torus, with inner diameter 126 meters, radius of tube 25 meters.
Want to do more calculations like this, try the Volume of a Torus and Surface Area of a Torus online calculators. The volume one uses diameters, the surface area one uses radii so need to keep that in mind when working with them both at once.
The idea of the torus there is - easier than a balloon because you could launch right through it and leave it behind, undamaged, for next launch to use again.
Your spaceship is suspended in the atmosphere, no need for ground support, just needs to be held from above. So, I think all you need are tethers to tether it to the torus - those are low weight, adds a few more tons, so haven't bothered to take account of those in the calculation.
So - if you can deliver the weight to Venus - or else - generate the fuel on Venus - suspending the rocket next to your habitat for lift off probably isn't a huge engineering issue. And once you've got it to Venus - could use it to shuttle back and forth to orbit around Venus - so long as you generate the fuel on Venus itself. Or import fuel.
I'm assuming 1 kg / m2 similar to the fabric used for the Cargolifter (28 ounces a square yard = 0.95 kg / m2).
These are maximum payloads, doesn't have to launch with as much mass as that of course.
I think more useful right now as a way of showing how impractical Mars colonization is rather than as a way of showing how Venus is a good place to colonize. Deserts of Earth far better for colonization than either.
But in our solar system, I think Venus upper atmosphere comes a rather close second to the most inhospitable of the Earth deserts, maybe an easier place to live in some ways than the summits of the Himalayas indeed.
While Mars would be far harder to colonize than a Himalayan summit, surely.
So - it's just possible some Earth life could live there - or gradually adapt to live there in interface between human habitat and the atmosphere. And could be native life there which if so has I think personally - major planetary protection impact the other way for return to Earth in case it is some novel form of life e.g. XNA.
Is very indirect evidence suggesting possibility of life in the Venus clouds, not at all conclusive, just slightly suggestive - particles the right size, non spherical - and chemical in the atmosphere normally associated with life on Earth, but could be created by non life processes there. COSPAR passed a Venus sample return as of only minor planetary protection issues - but that was some time back and I think a new investigation now, if someone planned a sample return, might possibly come to another conclusion.
Before we send humans to the Venus clouds we need to check what effect they would have on Venus ecosystem if it has any.
If Venus is lifeless, still need to think through the effects of introducing life to the atmosphere. At first sight - no major issues in that case - a much simpler situation than Mars with its varied terrain that life could inhabit - but this certainly needs a thorough study also. That's because there is no way of turning back the clock - if we introduce life to Venus and it turns out that some forms of Earth life can live in the Venus atmosphere.
If that happens the life would transform the Venus upper atmosphere and clouds. That might well be beneficial to colonists - but the possible effects still would need to be checked.
That's just because, whenever there's a whole planet at stake, and an action we can do will change it irreversibly - we owe it to future generations to proceed with caution, and study first before we act. No matter how promising it seems, we shouldn't just dive in and hope for the best without due diligence checking possible issues first.
Also - if it's likely that we might terraform Venus - have to think longer ahead - what happens to all the floating cloud cities during the terraforming process?
So again in my view, a Stanford Torus in space - if it can be made low maintenance wins hands down over almost all other ways of building large colonies in space, if we ever wanted to do it.
But a Buckminster Fuller type tensegrity sphere floating in the Venus atmosphere might well be easier to build than a Stanford torus - and easier to maintain.
And has advantage that you can start small with smaller habitats, still able to float in the dense atmosphere - and also far easier to construct than any other habitat we could construct in space, mainly using materials extracted from the atmosphere itself plus a few things dredged up from surface of Mars.
Startup colonies would be launched from Earth - but later on you'd supply using materials from NEOs etc just as for the Stanford Torus - with aerobraking easy to deliver to Venus - and it would also use materials sourced from the Venus atmosphere and surface.
Nowhere is better than Earth, even in worst conceivable disaster. Those who argue that a Mars colony, say, would survive better seem to assume that you have technology on Mars that we don't have on Earth.
If you make it a level playing field - you assume that Earth and the space colonies have access to the same technology, then if space colonies have 3D printers to print spaceships - so does Earth. In that situation any survivors on Earth even after worst possible disaster you can imagine have far better chance of rebuilding civilization than anyone on Mars or in the Venus atmosphere.
That's true even when you get large Stanford toruses or Venusian floating cities - will be a while before they can build spaceships for themselves and until then they are dependent on Earth. When it is easy for them to build spaceships - then it is really easy to make them on Earth - and many other things also would be much easier for us also, and world would be changed in countless ways, hard to anticipate what we would want or need in that situation.
For more about all this, I wrote an article about it some time back, on Science20.com. which links to the articles by Geoffrey Landis and others on the subject, and talks a bit about the 1970s Russian plans for Venus cloud colonies.
Will We Build Colonies That Float Over Venus Like Buckminster Fuller's "Cloud Nine"?
See also Could humans someday colonize the clouds of Venus? and Why are we thinking about a Mars colony when a Venus colony would be more technically feasible? It seems that radiation shielded floating colonies could be assembled on Venus, with plastic film and aluminum wire bags, filled with breathable air.
I'd say that in many ways the Venus cloud tops are more habitable and would be easier to colonize, though neither is anything like as habitable as even the harshest deserts on the Earth. Yes we haven't colonized the atmosphere of the Earth, we don't have "Cloud nine" type habitats floating above our mountains. But we could do. We could also colonize deserts, or the sea floor, or have floating sea cities. All of these I think are far more habitable and easier to colonize than Mars, for less cost, and more sustainable.
Venus - I think may be between the two, not as easy as Earth but many advantages over Mars, when you think it through. But I don't think you'd go to either place if your main motivation is to find an easy place to build a house. In the entire solar system, surely the Earth is by far the obvious place to build homes for humans. Even on mountain tops, or in cloud cities or deserts, nothing else compares with Earth.
I'd argue the same way as Geoffrey Landis. Being able to build without need to engineer to contain multiple tons per square meter - and without need to add meters thickness of radiation shielding is a huge advantage.
If you want a one way mission, then Venus and to stay is better than Mars. Because also - you have the advantage of being able to land using a normal parachute as for Earth, can't do that on Mars. And delta v slightly less. And no hard surface to hit - so long as your habitat or hydrogen balloon opens out at some point around the right level during the slow descent by parachute - then you are fine. No need for fraction of a second precision landing maneuvers.
The lifting force on Venus is huge if you build big habitats - and - you can build them huge without much material. It's like an airship - but filled with ordinary atmosphere rather than helium, because the Earth's mainly nitrogen atmosphere is a lifting gas in the mainly CO2 atmosphere of Venus - and you can of course use hydrogen as a lifting gas as well - e.g. for smaller vehicles.
We have already sent balloons to the upper Venus atmosphere, Venera balloons from Russia. Russia actually had ideas for Venus cloud colonies back in 1970s
The sulfuric acid is not nearly as much as a disadvantage as suggested. After all we have sulfuric acid plants, and know how to build machinery to deal with sulfuric acid.
Only the exterior of the habitat - and of any suits or aircraft that need to go out into the atmosphere need to be protected.
As for the crushing heat if you fall -well if you fall on Mars and e.g. break the visor of your spacesuit - or tear it or some such - you will die in seconds from breach in your spacesuit because of the thin almost vacuum atmosphere.
If you fall in the Venus atmosphere - there is some time for rescue - and you can be tethered to the habitat etc. I'd say in terms of safety for humans outside of the habitat, that Venus wins hands down over Mars. Manly because your protection suit is much lower tech. Instead of a spacesuit, you just need protection from the sulfuric acid, and oxygen breathing equipment, and can equalize pressure inside and out.
As for hit by incoming spaceship - that's a major issue for any space colony. With the Venus ones - well if it is just some debris creating holes - remember that inside and out is at same pressure so won't explosively decompress no matter how many holes there are. Just gradual diffusion of the atmosphere. And an incoming spaceship will be floating in parachutes - or if not - would burn up in the atmosphere (while on Mars won't burn up so easily if it comes in fast). So again, Venus scores over Mars.
MAJOR ADVANTAGES
- Lightweight construction of the habitats. Same launch mass gives a far far more spacious habitat to live in at the destination and more space to grow plants
- Just about everything you need for growing plants exists in the atmosphere - including large quantities of nitrogen - and - obviously - sulfur. Also water easily extracted from the atmosphere. Apart from a few trace elements, you have all the materials you need to grow trees - and organic plastics - and build new habitats utilizing materials from the atmosphere. When you take account of water as also coming from atmosphere - 90% of the mass of a tree comes from the atmosphere.
- Low tech construction compared with any other space habitat. Can imagine it being maintained for some years - and possibly indefinitely in a large enough colony - with fairly low technology - especially if you can get plants to create the oxygen and a biosphere like enclosed habitat - even mobility suits for EVAs outside the habitat are more at the technology level of aqualungs than a modern spacesuit - while a Mars habitat requires high technology through to the foreseeable future, centuries at least, for the construction of habs, and spacesuits.
If things go seriously wrong inside, all the machines stop working - well you already have the temperature and pressure of an Earth atmosphere without any use of machinery to create it. If you can manage to generate the oxygen with algae and plants - seems pretty feasible from Earth experiments in Russia - then you can probably manage at least a year or two in a large habitat with hardly any use of electronics at all (unless needed for night time solar radiation for plants - but algae and many microbes,at least, would manage fine with 48 instead of 12 hour periods of darkness). While everyone on a Mars settlement would die pretty soon, if you had problems with supply of electricity for the machines, or if important components of them failed. - You can still mine the surface of Venus - are methods of doing that by dropping a cable to the surface to dredge materials - buoyed by small hydrogen or helium balloons every few kilometers so can use ordinary strength cables
- Plentiful sunlight (Mars has much less sunlight than Earth)
- Protection from cosmic radiation and solar storms, and fair amount of UV light protection
- At cloud tops of Venus - so would be able to see the sun - and spectacular views of the clouds
- Can go outside the habitat with a thin suit so long as it has breathing apparatus and protects from the sulfuric acid.
No limitation on exposure - unlike Mars where you would have a maximum lifetime period on the surface - otherwise get significant risk of cancer (and early in your life, not late in life as for smoking) - and young children probably never allowed to leave a habitat at all and have to spend their lives shielded from cosmic radiation. - Totally protected from micro-meteorites - and larger meteorites very rare, less than for Earth (Mars is several times more dangerous than Earth for asteroid impacts, because of proximity to asteroid belt and thin atmosphere)
- Same pressure inside and outside the habitat - so if you do get damage - it's a slow leak exchanging air inside and out - not an instant breach. You could repair the leaks every few months rather than needing an instant emergency fix.
- Day length is reasonable in upper atmosphere as winds take your habitat around Venus roughly every 4 days. That might be okay for plants - and if not - well you have abundant solar power - and easy to store for night time use (one way is to simply have a weight suspended from a cable below the habitat - raise it in the daytime using solar power, let it fall at night to generate night time power).
- By far the easiest planetary or moon surface to import mass from elsewhere in the solar system, with exception of Earth - through aerobraking and parachutes.
WE DON'T HAVE PEOPLE LIVING IN AEROSTATS ON EARTH - BUT THEY DON'T LIVE ON HIMALAYAN SUMMITS EITHER
It's true we don't have people living in aerostats on Earth. But we don't have them living on the summits of the Himalayas either in habitats- a better analogy than Antarctica or high arctic - because having breathable oxygen in the air is a huge advantage - as also is the plentiful water in form of ice.But summits of Himalayas are some orders of magnitude easier places for humans to live than Mars surface. You wouldn't need to engineer to withstand tons per square meter outwards pressure or add meters of cosmic radiation shielding to cover your habitat, and could get oxygen from atmosphere no need to split it from water.
Also do have Buckminster Fuller's Cloud Nine (tensegrity sphere)
Never been built, but seems practical enough, if you work through the engineering details - I think that's generally agreed (though might surprise you if you haven't looked into it) just don't need them here enough to want to build one. A cloud nine in Venus atmosphere doesn't even need to be warmer than the surrounding air.
So have a road map to build entire cities in the Venus atmosphere in the future.
RETURN TO EARTH FROM VENUS
As for return to Earth - yes you need to have boosters floating in the atmosphere. Later on you could create the fuel from the Venus atmosphere - abundant solar power.To start with - yes do need to send rockets there and have them float in the atmosphere next to the colony ready to return. Expensive but do-able - not sure it is enormously harder than sending a rocket to Mars able to return to Earth - needs someone with the brilliance of Robert Zubrin to work on the engineering details, I think they would find a solution.
Has one advantage - no need for careful touch down on a hard surface. Just need parachute to slow down - and then hydrogen balloon inflates when it is at the right level in the Venus atmosphere - and you have a rocket suspended in the atmosphere next to the habitat ready for return trip.
SIZE AND WEIGHT OF HYDROGEN BALLOON TO SUSPEND FULLY LOADED ROCKET IN VENUS ATMOSPHERE READY FOR LAUNCH
I did a rough calculation here could be useful first ballpark figure:Calculation of the size of torus, filled with hydrogen, needed to suspend a Soyuz, fueled for lift off, in the Venusian atmosphere next to a cloud colony
Hydrogen is a slightly stronger lifting gas for Venus with denser CO2 atmosphere - and of course no concerns at all of combustion.
Hydrogen has a density of 0.0899 Kg/m3. and Carbon Dioxide, 1.977 kg/ m3, for air it is 1.205 kg / m3
.
So a hydrogen balloon on Venus has lifting power of 1.8871 kg per m3, compared with 1.1151 kg / m3 on Earth
To counteract the mass of a fully fueled Soyuz - lift off mass lift off mass 308 metric tons (not sure of lift off mass for the latest TMA-M), then you would need 308,000/ 1.8871 = 163,213 m^3
That could be more than supplied by a torus filled with hydrogen with radius 50 meters and with the radius of the tube around 14 meters. Volume 193444 m3. Lifting capacity 365 tons.
Surface area 27634 m2, so if you had fabric weighing 1 kg / m2 that's 28 tons for the fabric
As a bonus, if we make the torus able to expand to a larger size, like a weather balloon, then it could lift the Soyuz high into the Venus atmosphere before take-off.
If you want to suspend a Falcon Heavy fully loaded for take off - that's a little under 5 times the mass, would need 775,175 m3, so need torus, with inner diameter 126 meters, radius of tube 25 meters.
Want to do more calculations like this, try the Volume of a Torus and Surface Area of a Torus online calculators. The volume one uses diameters, the surface area one uses radii so need to keep that in mind when working with them both at once.
The idea of the torus there is - easier than a balloon because you could launch right through it and leave it behind, undamaged, for next launch to use again.
Your spaceship is suspended in the atmosphere, no need for ground support, just needs to be held from above. So, I think all you need are tethers to tether it to the torus - those are low weight, adds a few more tons, so haven't bothered to take account of those in the calculation.
So - if you can deliver the weight to Venus - or else - generate the fuel on Venus - suspending the rocket next to your habitat for lift off probably isn't a huge engineering issue. And once you've got it to Venus - could use it to shuttle back and forth to orbit around Venus - so long as you generate the fuel on Venus itself. Or import fuel.
MASS OF HABITAT ITSELF
As for mass of the habitat itself - if you just use Earth atmosphere as lifting gas - then it's half the lifting power of helium, roughly half a kilogram for a meter cube of atmosphere.I'm assuming 1 kg / m2 similar to the fabric used for the Cargolifter (28 ounces a square yard = 0.95 kg / m2).
So for example, suppose it's a 100 meter radius balloon.
r = 100 m
V = 4188790 m3
A = 125664 m2
C = 628.319 m
works out at Max 2,094 tonnes total, and Max 16.5 kg per square meter of surface area.
Assuming 1 kg / m2 for the fabric, that's 126 tons of fabric
If you go up to a cloud nine like 1000 meter radius you get 2,094,395 tons total, and 165 kg per square meter of surface area.
r = 64 m
V = 1098070 m3
A = 51471.9 m2
C = 402.124 m
Max payload 549 tons. Max 10 kg per m2.
51 tons of fabric
For a smaller start up colony
r = 29 m
V = 102160 m3
A = 10568.3 m2
C = 182.212 m
Max payload 51 tons, Max 5 kg / m2.
11 tons of fabric.
(if you want to do more of these, the online Sphere Calculator may save a bit of time).
These are maximum payloads, doesn't have to launch with as much mass as that of course.
VENUS UPPER ATMOSPHERE CLOSE SECOND TO MOST INHOSPITABLE EARTH DESERTS
I'd say Venus atmosphere is an easier place for humans to live than Mars surface - though not nearly so easy as Earth.I think more useful right now as a way of showing how impractical Mars colonization is rather than as a way of showing how Venus is a good place to colonize. Deserts of Earth far better for colonization than either.
But in our solar system, I think Venus upper atmosphere comes a rather close second to the most inhospitable of the Earth deserts, maybe an easier place to live in some ways than the summits of the Himalayas indeed.
While Mars would be far harder to colonize than a Himalayan summit, surely.
PLANETARY PROTECTION ISSUES - LIFE IN VENUS CLOUDS
Venus does have some planetary protection issues. There just possibly might be life there - sulfuric acid levels could possibly be tolerated by extremophiles, and they'd have trouble staying aloft but not so bad as Earth as residence time for particles at that level, microbe sized, is months rather than days - so need some way of working around that to maintain a population in the high atmosphere - seems not impossible.So - it's just possible some Earth life could live there - or gradually adapt to live there in interface between human habitat and the atmosphere. And could be native life there which if so has I think personally - major planetary protection impact the other way for return to Earth in case it is some novel form of life e.g. XNA.
Is very indirect evidence suggesting possibility of life in the Venus clouds, not at all conclusive, just slightly suggestive - particles the right size, non spherical - and chemical in the atmosphere normally associated with life on Earth, but could be created by non life processes there. COSPAR passed a Venus sample return as of only minor planetary protection issues - but that was some time back and I think a new investigation now, if someone planned a sample return, might possibly come to another conclusion.
Before we send humans to the Venus clouds we need to check what effect they would have on Venus ecosystem if it has any.
If Venus is lifeless, still need to think through the effects of introducing life to the atmosphere. At first sight - no major issues in that case - a much simpler situation than Mars with its varied terrain that life could inhabit - but this certainly needs a thorough study also. That's because there is no way of turning back the clock - if we introduce life to Venus and it turns out that some forms of Earth life can live in the Venus atmosphere.
If that happens the life would transform the Venus upper atmosphere and clouds. That might well be beneficial to colonists - but the possible effects still would need to be checked.
That's just because, whenever there's a whole planet at stake, and an action we can do will change it irreversibly - we owe it to future generations to proceed with caution, and study first before we act. No matter how promising it seems, we shouldn't just dive in and hope for the best without due diligence checking possible issues first.
Also - if it's likely that we might terraform Venus - have to think longer ahead - what happens to all the floating cloud cities during the terraforming process?
COMPARISON OF CLOUD NINE TENSEGRITY SPHERE IN VENUS ATMOSPHERE WITH STANFORD TORUS
Stanford Torus if it could be built, then huge advantage of a big spacious multiple square kilometer habitable volume built with ideal temperature, gravity, and air pressure - might even be as easy a place for humans to live as the tropics - if it can be made low maintenance. Also, buildable even with 1970s technology but disadvantage of a huge initial investment to build it in the first place.So again in my view, a Stanford Torus in space - if it can be made low maintenance wins hands down over almost all other ways of building large colonies in space, if we ever wanted to do it.
But a Buckminster Fuller type tensegrity sphere floating in the Venus atmosphere might well be easier to build than a Stanford torus - and easier to maintain.
And has advantage that you can start small with smaller habitats, still able to float in the dense atmosphere - and also far easier to construct than any other habitat we could construct in space, mainly using materials extracted from the atmosphere itself plus a few things dredged up from surface of Mars.
Startup colonies would be launched from Earth - but later on you'd supply using materials from NEOs etc just as for the Stanford Torus - with aerobraking easy to deliver to Venus - and it would also use materials sourced from the Venus atmosphere and surface.
FOR THE FUTURE, DON'T NEED ANYWHERE OUTSIDE OF EARTH TO COLONIZE RIGHT NOW (OPINION)
Personally - I see this as a useful thing to be able to do in the future rather than anything we need urgently right now.Nowhere is better than Earth, even in worst conceivable disaster. Those who argue that a Mars colony, say, would survive better seem to assume that you have technology on Mars that we don't have on Earth.
If you make it a level playing field - you assume that Earth and the space colonies have access to the same technology, then if space colonies have 3D printers to print spaceships - so does Earth. In that situation any survivors on Earth even after worst possible disaster you can imagine have far better chance of rebuilding civilization than anyone on Mars or in the Venus atmosphere.
That's true even when you get large Stanford toruses or Venusian floating cities - will be a while before they can build spaceships for themselves and until then they are dependent on Earth. When it is easy for them to build spaceships - then it is really easy to make them on Earth - and many other things also would be much easier for us also, and world would be changed in countless ways, hard to anticipate what we would want or need in that situation.
For more about all this, I wrote an article about it some time back, on Science20.com. which links to the articles by Geoffrey Landis and others on the subject, and talks a bit about the 1970s Russian plans for Venus cloud colonies.
Will We Build Colonies That Float Over Venus Like Buckminster Fuller's "Cloud Nine"?
See also Could humans someday colonize the clouds of Venus? and Why are we thinking about a Mars colony when a Venus colony would be more technically feasible? It seems that radiation shielded floating colonies could be assembled on Venus, with plastic film and aluminum wire bags, filled with breathable air.
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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