Well the ISS always has a crewed spacecraft attached to it as a "lifeboat" - so they can use that to return to Earth at any time. That also sets a limit on the number of crew on the ISS. When there are six crew resident, they have two of the Soyuz vehicles permanently docked to the ISS.
As for natural disasters - the chance even of a giant asteroid impact is absolutely tiny. Chance of the Dinosaur extinction event size asteroid before 2100 (10 km across) 0.00001% and will be even less by 2020 when we complete mapping of 90% of all NEOs larger than 140 meters across.
See What is the probability of a significant asteroid impact event by 2100?
And we'd surely have at least a few months notice of anything as big as that so could plan for it.
So - don't think you need to bother about them finding a habitable area of the Earth to land in :). Even a few hours after the dinosaur impact, after the firestorm caused by the impact is over, and the tsunamis it caused, and the landing site itself has cooled down a bit - and the flying rocks from the impact debris no longer falling out of the sky - you could land probably even close to where the asteroid hit the Earth no problem..
And - is no different from a normal re-entry from space - except - if you landed in a remote place with no support staff around to help you it would be some hours / days before you could walk around normally after a long flight. That could be an inconvenience if there is nobody there to help you.
But surely there would be people around to help you.
If you can think of a disaster with nobody on the ground to help you - then it would indeed be a major issue, because most astronauts can't even walk after a long duration spaceflight for a few hours. They'd have to sit inside their soyuz until their strength returned enough to stumble out - and then it would - for most astronauts, be a day or two before they can walk around with some semblance of normality and about 3 weeks before they return to normal levels of co-ordination etc.
If they are in a remote place with wolves around or lions or whatever, they might be best advised to just stay in the Soyuz for some days, do what minimum excercise they can, get out and stretch a bit from time to time but return to it for safety. And then after a few days - okay they'd be getting really hungry by then but better than taking the risk of wandering around totally helpless hardly able to walk. Some astronauts / cosmonauts recover much more rapidly than others and may be able to manage for themselves even perhaps by the next day.
I can't imagine a scenario where that would apply. Just for purposes of completeness to answer your question. They would still survive but would have a rather horrid 2 or 3 days. Avoid landing in Siberia or Canada obviously, or in the sea, if nobody is there to rescue you.
As for natural disasters - the chance even of a giant asteroid impact is absolutely tiny. Chance of the Dinosaur extinction event size asteroid before 2100 (10 km across) 0.00001% and will be even less by 2020 when we complete mapping of 90% of all NEOs larger than 140 meters across.
See What is the probability of a significant asteroid impact event by 2100?
And we'd surely have at least a few months notice of anything as big as that so could plan for it.
So - don't think you need to bother about them finding a habitable area of the Earth to land in :). Even a few hours after the dinosaur impact, after the firestorm caused by the impact is over, and the tsunamis it caused, and the landing site itself has cooled down a bit - and the flying rocks from the impact debris no longer falling out of the sky - you could land probably even close to where the asteroid hit the Earth no problem..
And - is no different from a normal re-entry from space - except - if you landed in a remote place with no support staff around to help you it would be some hours / days before you could walk around normally after a long flight. That could be an inconvenience if there is nobody there to help you.
But surely there would be people around to help you.
If you can think of a disaster with nobody on the ground to help you - then it would indeed be a major issue, because most astronauts can't even walk after a long duration spaceflight for a few hours. They'd have to sit inside their soyuz until their strength returned enough to stumble out - and then it would - for most astronauts, be a day or two before they can walk around with some semblance of normality and about 3 weeks before they return to normal levels of co-ordination etc.
If they are in a remote place with wolves around or lions or whatever, they might be best advised to just stay in the Soyuz for some days, do what minimum excercise they can, get out and stretch a bit from time to time but return to it for safety. And then after a few days - okay they'd be getting really hungry by then but better than taking the risk of wandering around totally helpless hardly able to walk. Some astronauts / cosmonauts recover much more rapidly than others and may be able to manage for themselves even perhaps by the next day.
I can't imagine a scenario where that would apply. Just for purposes of completeness to answer your question. They would still survive but would have a rather horrid 2 or 3 days. Avoid landing in Siberia or Canada obviously, or in the sea, if nobody is there to rescue you.
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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