I see many advantages for space stations and very few for planetary surfaces, especially Mars.
The Moon has some advantages over space stations, because it is so close and has lunar caves and perpetual sunlight at the poles and probable ice there. Venus upper atmosphere also in longer term because it could permit very lightweight construction of huge habitats. .
But all of these are so much more inhospitable than Earth, none of them seem likely to give any security or advance towards becoming an interplanetary species - if anything goes wrong, you'd come straight back to Earth as by far the most hospitable place for humans in the solar system.
If we do manage to make closed system self contained space stations or habitats - still - they would be far easier to build and maintain on the Earth than in space - even after the worst possible future disasters on Earth.
Space stations in space do have a couple of advantage over Earth, and also over other planets. You can set them to any gravitational level through adjusting the spin rate. If it turns out that the optimal level of gravity for health is less than full g, we might be healthier in a space station. If it turns out to be better for health to have varying gravity - we can do that too in a space station by having smaller spinning centrifuges for the higher g levels inside the larger centrifuge of the space station itself.
But so far, nobody knows what the optimal level of gravity for health is. Most assume that full g 24/7 is optimal for a human because that is what we have evolved to live in. But there is no data from space for human health in gravity levels between full g and zero g except the few days of lunar g of the human astronauts on the Moon - and we can't simulate it on Earth. And the human body is far too complex to hope for an accurate prediction of the effects of intermediate gravity from the data for zero g, full g, and hyper gravity.
They are also not affected in any way by weather - no dust storms to block out the sun as on Mars, and no hurricanes as on Earth. You construct them with whatever climate you want them to have, and put them wherever you want in the solar system (with near future technology).
Resources are as easy to find in space as on a planetary surface. And as easy to supply to your station.
This may be your first surprise. We tend to think that the place to look for resources for colonization must be the surfaces of planets, because we live on one. But there are abundant resources in space too. The most important thing for making habitats is water. Liquid water is scarce in our solar system. Ice however is abundant, and many asteroids have significant quantities.
Yes space is largely empty with lots of space between the rocks, but what matters there is the delta v to get from one to the other, not the distance, because in space once you set things moving in a new direction, they just keep going until they reach wherever you targeted.
So, you'd start with a particular asteroid. If you use a NEA, say 300 meters across if you choose the right one , it will have most of the materials you need to build your habitat already.
Then the delta v to move material from one asteroid to another in a similar orbit around the sun isn't that great. And water can be used as rocket fuel so it is easy to move the resources to where they are needed, so long as you have a source of water. And on a planetary surface you'd need to move resources around also, and in vacuum conditions just as in space - it may well be harder that way.
Metals are also abundant in asteroids, as also are organics in some kinds of asteroid.
Some of the interesting types of asteroid are:
Once you have water, you can extract oxygen to create an atmosphere. It's also easy to find carbon compounds in space too, in asteroids. Metals are easy to find in space, indeed one of the first uses of metal on Earth was probably meteoritic iron.
Mars has some organics, but there is some process continually destroying it on the surface as it has far less than you'd expect from the continual infall of meteorites and micrometeorites.
For orbits around Earth, the Moon, or other orbits close to the Earth, Near Earth Asteroids may have almost all the materials you need you need to set up a colony.
For orbits around Mars or close to Mars, then the Martian moons Phobos and Deimos are a natural choice. The composition of the Maritan Moons is not too well understood. Deimos seems either C or D type. Either way it might have water beneath the surface. It has a low density which might suggest water ice. David Kuck in 1997 suggested starting up a Deimos Water Company to supply Earth orbit with water from Deimos. The Kuck mosquitoes are small unmanned craft that drill into Deimos and extract water from below the surface, use part of it as fuel to transport the rest back to Earth.
If you take the long term view, if you are building a large colony that will take maybe decades to complete, then you don't need to worry too much about where to get the materials from because with gravity assist and a bit of delta v you can get them from anywhere in the solar system via flybys of the planets and moons, and there is plenty of ice to use as fuel for the delta v to move it around.
As for cabon dioxide - well you've got organics in asteroids, even better. And in a spaceship or habitat normally CO2 is something you produce as a waste product to get rid of. It's an advantage on Mars for creating fuel - but in space you need less fuel anyway, to get around, and no need to escape a planets gravity pull go get back to Earth, and you still need a feedstock of hydrogen to use it to create fuel on Mars.
See my Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
We are used to mining on a planetary surface. But we find it easier here because water is liquid and can be used as a lubricant, and because we can breath the air. Mining on Mars just as for asteroids has to deal with vacuum conditions. It will probably be much easier to use totally automated methods such as mining moles for drilling.
Humans are useful for trouble shooting, but they can operate remotely by telepresence. Or they can use spacesuits, but will this be any easier on a planetary surface?
For operations you need to do under gravity, you can take the resources into your habitat which would have components spinning for gravity - e.g. tethered spin. And if you don't need gravity, then it's much easier to move huge multi-ton rocks around in zero g than on a planetary surface.
We don't have any experience yet of either, of commercial mining on a lunar or planetary surface, or in space. We may get many surprised. But neither will be much like mining on Earth and there is plenty of reason to suppose it could be easier to do in space than on a planet with a vacuum or near vacuum for an atmosphere.
We are used to living on a planetary surface, but also used to having a breathable atmosphere. Make it so that you have to wear spacesuits all the time and create all your own oxygen and many of the advantages of living on a planet surface go away.
E.g spacesuits are very clumsy. Have you seen the Apollo astronauts trying to pick things up or to drill into the lunar surface?
Then, if you have an accident, while working - drop something, tear your spacesuit, fall, etc - you die.
Just walking around out of doors is as dangerous as cave diving - you are totally dependent on oxygen. E.g. if you get an injury or are delayed in any way and can't get back to your base in time before your air runs out, you die.
You will need to be aware all the time of how much oxygen you have left, and how far it is to the nearest oxygen supply point and how long it will take you to get there and whether you have enough reserve left, allowing for emergencies, things breaking down, etc.
So you have to be very disciplined, and take many safety measures, clumsy people and forgetful people will surely die. And careful people also if they make mistakes.
If you spend too much time out of doors anyway, radiation exposure levels increase, increasing your lifetime risk of cancer. Most people won't want more than a couple of years total of time spent in a spacesuit on the surface in their lifetime.
So probably most people will spend most of their time indoors.
It's hard to beat this huge advantage of Earth, that we can breath the atmosphere.
Or you build really big habitats - city dome type habitats, kilometers in diameter. Those would work - for similar reasons to space stations - as places to live anyway. You don't need to wear a spacesuit because you spend your entire life in a huge dome.
These could perhaps work on a planetary surface. Still - not sure that they would be any easier to build than a space station - perhaps we can find out more as we develop both technologies.
Such habitats on Mars would be especially vulnerable to meteorite impact - so would need meteorite shielding and defense - Mars gets about ten times as many as Earth because it's closer to the asteroid belt, and instead of burning up in the upper atmosphere as a fireball they get all the way down to the surface.
This is the first meteorite ever found on another planet
Roughly the size of a basketball, iron -nickel meteorite,. discovered by NASA's Mars Exploration Rover Opportunity in 2005
So you'd need meteorite shielding, and you'd need cosmic radiation shielding. Ends up pretty much similar to a space habitat in that respect. And not sure the gravity is an advantage, it might make it more difficult.
These are a major asset for building habitats inside. But also available on the Moon and not sure Mars has any advantage there. This is one of the few things I think does count as an advantage on a planet or Moon compared with space habitats, potentially at least.
The CO2 value I think vastly over rated - because CO2 is a waste gas - the ISS vents it all the time. It is poisonous to humans at levels of about 1$ in the atmosphere.
What's the value in pumping it in from the near vacuum of the atmosphere?
In some special situations it is useful to make fuel - but you can also use the same process, the Sabatier reaction, to make fuel from exhaled CO2 from plants and astronauts. And you need much more fuel on a planet surface to power all the rovers. And you'd have plenty of power anyway in a big space habitat from solar power, and can use water for reaction mass or split it to make hydrogen and oxygen.
So in short this idea of using CO2 for fuel is used to solve a problem that you only have if you live on a planetary surface in the first place.
Space stations rotating to give artificial gravity can give full g or any level in between. We don't know what level is needed for human health long term so haven't got anything to go on to know if it is healthy to live on Mars or the Moon yet.
It's not easy to extract resources if you are in a spacesuit, so you'd use machines, same also for asteroid mining.
But asteroid mining is in many ways going to be much easier without gravity. Because you just need to push the material in whatever direction you want to send it and let go. Probably using a similar method to the way Maglev trains work - i.e. a mass driver. No need to drive around in rovers to carry materials from place to place.
There is no liquid water to lubricate your drill shafts for mining on Mars or the Moon so can't use conventional mining techniques anyway.
In space you can have sunlight 24/7, no need to worry about dust storms that can cut out 99.9% or more of the sunlight.
Your habitat is totally in your control, you can set it to receive whatever level of sunlight you need. Make it a place that feels like the tropics, or a clime from a higher latitude - there is plenty of sunshine in space, so just adjust the mirrors and shades or design in the right areas and that's it done.
You can experiment and make mistakes in a space habitat. Especially biological ones. If the species you are working with interact in strange ways or some microbe evolves that's a problem in worst case, you scrub its atmosphere and soil and start again. You can never start again with a planet if you make a mistake. You just have to move on and hope you find a solution - but what if you have taken a wrong turn and there is no solution to your problem?
Maybe after a few centuries of space habitats we'll know enough to decide to terraform or paraterraform a planet.
There is no hurry.
I don't think it should be our priority to become an interplanetary species either, don't share that premiss. Because whatever happens, the Earth will remain the most habitable place in our solar system.
There is no way we can mess it up to make it less habitable than Mars, and no natural disaster can do that either (not even the 10 km asteroid at the end of the dinosaur era made Earth anything like as uninhabitable as Mars - for that it would need to lose all its oceans and most of its atmosphere for starters).
So almost any solution we find that works in space will work far better as a way to build habitats on the Earth. About the only exceptions there I can think of are the likes of large scale thin film mirrors for solar power - and anything that depends on mining resources that occur as much richer ores in space - but with far future technology it probably won't be difficult to return those materials to the Earth.
So, for better or for worse, we depend on Earth and our priority instead should be to save and protect our Earth, there is no point in trying to escape from it.
About 500 million years from now, yes, Earth will probably become increasingly uninhabitable. Whatever species is living on Earth then will need to become interplanetary if it wants to survive. But we don't need to. Also, it is hard to see how anything much we can do now would help those beings half a billion years from now. We don't even know if they would be oxygen breathers, might be that they want an atmosphere of hydrogen sulfide or methane for instance. It's rather improbable that there will still be biologically identical humans by then.
So - I see these settlements as primarily for exploration, adventure, tourism etc rather than as a way to make our species interplanetary. I don't see any value in attempting that at this present time, though it is great to work on the ideas just in case they are useful for whatever species needs it 500 million years from now - but perhaps more so - because the ideas can also help us with smaller scale habitats, and may help us understand exoplanets - and maybe some day we may want to transform a planet, but not necessarily for colonization purposes.
As for available surface area, then in the asteroid belt alone there is enough material for building habitats with living area of 1000 times the land surface of the Earth. So we aren't going to run out of it any time soon.
Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
This is even without the planetary protection issues.
Except for Earth that is, obviously habitable for us.
The Moon seems useful because it is so easy to get to from Earth. We could usefully have settlements, for instance in lunar lava tube caves, or at its poles. Because the cave habitats are already formed, cosmic radiation shielding, if they exist, and because you can get back to Earth in a couple of days in an emergency.
But Mars, I don't see as being of value there. If it is, needs to be for some reason like that. I think if you look into it in detail, it's not the obvious place to start at least.
The upper Venus atmosphere does have an advantage over space stations however. Permits far lighter weight construction because pressure is equalized inside and out. Radiation shielding. And can go out of doors with just an air breather and acid protection, but no bulky spacesuit needed.
Whether that's enough advantage to make it preferable to a space station, I don't know. Might be. You'd need some good reason though for living in the Venus atmosphere. Because Earth would still be a far better place to build a home.
As for Mars main reason for living there would be to study Mars and find out about whether there is life there or not. But if that is your priority, then the last thing you want to do is to land humans there, until you know what effect that would have on life there.
So for Mars, I see it a case of finding if there is any life there first, or what else there is there, and leaving any decisions about whether to send humans there or not for later once we know more about the planet.
And if we ever do introduce life to Mars - if it was as uninhabitable for Earth life as the Moon, no big deal. There is no problem bringing life to the Moon, because there are no habitats and no way for it to spread - at most you get local contamination which you'd avoid close to regions where the scientists are studying organics on Mars (e.g. near ice deposits).
But if Mars does have places where Earth life could reproduce - and if that life can spread in the dust storms or any other way - well as well as making sure we thoroughly understand Mars potential habitats first, and what there is there already, if anything - better to make our mistakes in space stations first before we think about possibly introducing new life irreversibly to Mars.
Hopefully this gives some things to think over - we so often here the case for planetary surfaces these days, but there is a strong case for space station type habitats - the scientists who designed the Stanford Torus and the O'Neil Cylinders had good reasons for favouring that approach.
With humans in orbit around Mars or on its moons, they could explore the surface with telepresence - and actually experience Mars more directly than if you were there in person in a spacesuit. So that includes tourists, if that happens - much better experience of exploring the Valles Marineres, say, from orbit via telepresence using avatars on the surface.
And everything you see is automatically streamed as HD binocular vision, and also haptic feedback, so others can then look at what you saw, just as you did. And any accidents will only damage repairable machines on Mars, not kill humans. And you can control rovers anywhere on the planet, jump from one to another, you see almost the entire planet at one point or another (twice a day in some orbits) - and Mars looks great from orbit, the continually changing views as you sweep around Mars. On the surface you'd be trapped in one place and liable to see nothing at all during dust storms.
So - there are many reasons for supposing our equivalent of Antarctic bases, for Mars, if we do send humans there, will be in orbit or on Phobos or Deimos.
See my Telerobotic Avatars On Mars With Super-Powers ("Teleporting" from orbit) - Search For Life - And Long Term Exploitation
and To Explore Mars With Likes Of Occulus Rift & Virtuix Omni - From Mars Capture Orbit, Phobos Or Deimos
See also Trouble With Terraforming Mars
and Imagined Colours Of Future Mars - What Happens If We Treat A Planet As A Giant Petri Dish?
The Moon has some advantages over space stations, because it is so close and has lunar caves and perpetual sunlight at the poles and probable ice there. Venus upper atmosphere also in longer term because it could permit very lightweight construction of huge habitats. .
But all of these are so much more inhospitable than Earth, none of them seem likely to give any security or advance towards becoming an interplanetary species - if anything goes wrong, you'd come straight back to Earth as by far the most hospitable place for humans in the solar system.
If we do manage to make closed system self contained space stations or habitats - still - they would be far easier to build and maintain on the Earth than in space - even after the worst possible future disasters on Earth.
ADVANTAGES OF SPACE STATIONS
Space stations in space do have a couple of advantage over Earth, and also over other planets. You can set them to any gravitational level through adjusting the spin rate. If it turns out that the optimal level of gravity for health is less than full g, we might be healthier in a space station. If it turns out to be better for health to have varying gravity - we can do that too in a space station by having smaller spinning centrifuges for the higher g levels inside the larger centrifuge of the space station itself.
But so far, nobody knows what the optimal level of gravity for health is. Most assume that full g 24/7 is optimal for a human because that is what we have evolved to live in. But there is no data from space for human health in gravity levels between full g and zero g except the few days of lunar g of the human astronauts on the Moon - and we can't simulate it on Earth. And the human body is far too complex to hope for an accurate prediction of the effects of intermediate gravity from the data for zero g, full g, and hyper gravity.
They are also not affected in any way by weather - no dust storms to block out the sun as on Mars, and no hurricanes as on Earth. You construct them with whatever climate you want them to have, and put them wherever you want in the solar system (with near future technology).
RESOURCES AS EASY TO FIND IN SPACE AS ON A PLANETARY SURFACE
Resources are as easy to find in space as on a planetary surface. And as easy to supply to your station.
This may be your first surprise. We tend to think that the place to look for resources for colonization must be the surfaces of planets, because we live on one. But there are abundant resources in space too. The most important thing for making habitats is water. Liquid water is scarce in our solar system. Ice however is abundant, and many asteroids have significant quantities.
Yes space is largely empty with lots of space between the rocks, but what matters there is the delta v to get from one to the other, not the distance, because in space once you set things moving in a new direction, they just keep going until they reach wherever you targeted.
So, you'd start with a particular asteroid. If you use a NEA, say 300 meters across if you choose the right one , it will have most of the materials you need to build your habitat already.
Then the delta v to move material from one asteroid to another in a similar orbit around the sun isn't that great. And water can be used as rocket fuel so it is easy to move the resources to where they are needed, so long as you have a source of water. And on a planetary surface you'd need to move resources around also, and in vacuum conditions just as in space - it may well be harder that way.
Metals are also abundant in asteroids, as also are organics in some kinds of asteroid.
Some of the interesting types of asteroid are:
- C-type carbonaceous - minerals with water content and carbon content. Some may have a high percentage of water. The most common type of asteroid.
- S type (stony) - metallic iron mixed with iron- and magnesium-silicates (common in inner solar system)
- M type (metallic) - good source of iron and nickel and other metals
- D type asteroids - organic rich, possibly water ice inside Rare in the inner solar system.
- Comets and extinct comets - source for water and organics.
Once you have water, you can extract oxygen to create an atmosphere. It's also easy to find carbon compounds in space too, in asteroids. Metals are easy to find in space, indeed one of the first uses of metal on Earth was probably meteoritic iron.
Mars has some organics, but there is some process continually destroying it on the surface as it has far less than you'd expect from the continual infall of meteorites and micrometeorites.
For orbits around Earth, the Moon, or other orbits close to the Earth, Near Earth Asteroids may have almost all the materials you need you need to set up a colony.
For orbits around Mars or close to Mars, then the Martian moons Phobos and Deimos are a natural choice. The composition of the Maritan Moons is not too well understood. Deimos seems either C or D type. Either way it might have water beneath the surface. It has a low density which might suggest water ice. David Kuck in 1997 suggested starting up a Deimos Water Company to supply Earth orbit with water from Deimos. The Kuck mosquitoes are small unmanned craft that drill into Deimos and extract water from below the surface, use part of it as fuel to transport the rest back to Earth.
If you take the long term view, if you are building a large colony that will take maybe decades to complete, then you don't need to worry too much about where to get the materials from because with gravity assist and a bit of delta v you can get them from anywhere in the solar system via flybys of the planets and moons, and there is plenty of ice to use as fuel for the delta v to move it around.
As for cabon dioxide - well you've got organics in asteroids, even better. And in a spaceship or habitat normally CO2 is something you produce as a waste product to get rid of. It's an advantage on Mars for creating fuel - but in space you need less fuel anyway, to get around, and no need to escape a planets gravity pull go get back to Earth, and you still need a feedstock of hydrogen to use it to create fuel on Mars.
See my Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
MINING EASIER IN SPACE
We are used to mining on a planetary surface. But we find it easier here because water is liquid and can be used as a lubricant, and because we can breath the air. Mining on Mars just as for asteroids has to deal with vacuum conditions. It will probably be much easier to use totally automated methods such as mining moles for drilling.
Humans are useful for trouble shooting, but they can operate remotely by telepresence. Or they can use spacesuits, but will this be any easier on a planetary surface?
For operations you need to do under gravity, you can take the resources into your habitat which would have components spinning for gravity - e.g. tethered spin. And if you don't need gravity, then it's much easier to move huge multi-ton rocks around in zero g than on a planetary surface.
We don't have any experience yet of either, of commercial mining on a lunar or planetary surface, or in space. We may get many surprised. But neither will be much like mining on Earth and there is plenty of reason to suppose it could be easier to do in space than on a planet with a vacuum or near vacuum for an atmosphere.
CLUMSY IN SPACESUITS
We are used to living on a planetary surface, but also used to having a breathable atmosphere. Make it so that you have to wear spacesuits all the time and create all your own oxygen and many of the advantages of living on a planet surface go away.
E.g spacesuits are very clumsy. Have you seen the Apollo astronauts trying to pick things up or to drill into the lunar surface?
ORDINARY ACTIVITIES AS DANGEROUS AS CAVE DIVING
Then, if you have an accident, while working - drop something, tear your spacesuit, fall, etc - you die.
Just walking around out of doors is as dangerous as cave diving - you are totally dependent on oxygen. E.g. if you get an injury or are delayed in any way and can't get back to your base in time before your air runs out, you die.
You will need to be aware all the time of how much oxygen you have left, and how far it is to the nearest oxygen supply point and how long it will take you to get there and whether you have enough reserve left, allowing for emergencies, things breaking down, etc.
So you have to be very disciplined, and take many safety measures, clumsy people and forgetful people will surely die. And careful people also if they make mistakes.
If you spend too much time out of doors anyway, radiation exposure levels increase, increasing your lifetime risk of cancer. Most people won't want more than a couple of years total of time spent in a spacesuit on the surface in their lifetime.
So probably most people will spend most of their time indoors.
It's hard to beat this huge advantage of Earth, that we can breath the atmosphere.
CITY DOME HABITATS
Or you build really big habitats - city dome type habitats, kilometers in diameter. Those would work - for similar reasons to space stations - as places to live anyway. You don't need to wear a spacesuit because you spend your entire life in a huge dome.
These could perhaps work on a planetary surface. Still - not sure that they would be any easier to build than a space station - perhaps we can find out more as we develop both technologies.
Such habitats on Mars would be especially vulnerable to meteorite impact - so would need meteorite shielding and defense - Mars gets about ten times as many as Earth because it's closer to the asteroid belt, and instead of burning up in the upper atmosphere as a fireball they get all the way down to the surface.
This is the first meteorite ever found on another planet
So you'd need meteorite shielding, and you'd need cosmic radiation shielding. Ends up pretty much similar to a space habitat in that respect. And not sure the gravity is an advantage, it might make it more difficult.
LAVA TUBE CAVES
These are a major asset for building habitats inside. But also available on the Moon and not sure Mars has any advantage there. This is one of the few things I think does count as an advantage on a planet or Moon compared with space habitats, potentially at least.
CO2 IS A SOLUTION TO A PROBLEM YOU ONLY HAVE ON A PLANETARY SURFACE
The CO2 value I think vastly over rated - because CO2 is a waste gas - the ISS vents it all the time. It is poisonous to humans at levels of about 1$ in the atmosphere.
What's the value in pumping it in from the near vacuum of the atmosphere?
In some special situations it is useful to make fuel - but you can also use the same process, the Sabatier reaction, to make fuel from exhaled CO2 from plants and astronauts. And you need much more fuel on a planet surface to power all the rovers. And you'd have plenty of power anyway in a big space habitat from solar power, and can use water for reaction mass or split it to make hydrogen and oxygen.
So in short this idea of using CO2 for fuel is used to solve a problem that you only have if you live on a planetary surface in the first place.
ANY LEVEL OF GRAVITY
Space stations rotating to give artificial gravity can give full g or any level in between. We don't know what level is needed for human health long term so haven't got anything to go on to know if it is healthy to live on Mars or the Moon yet.
WILL USE MACHINES FOR MINING ANYWAY IN VACUUM OR NEAR VACUUM CONDITIONS
It's not easy to extract resources if you are in a spacesuit, so you'd use machines, same also for asteroid mining.
But asteroid mining is in many ways going to be much easier without gravity. Because you just need to push the material in whatever direction you want to send it and let go. Probably using a similar method to the way Maglev trains work - i.e. a mass driver. No need to drive around in rovers to carry materials from place to place.
There is no liquid water to lubricate your drill shafts for mining on Mars or the Moon so can't use conventional mining techniques anyway.
SUNLIGHT 24/7 IN SPACE
In space you can have sunlight 24/7, no need to worry about dust storms that can cut out 99.9% or more of the sunlight.
Your habitat is totally in your control, you can set it to receive whatever level of sunlight you need. Make it a place that feels like the tropics, or a clime from a higher latitude - there is plenty of sunshine in space, so just adjust the mirrors and shades or design in the right areas and that's it done.
CAN MAKE BIOLOGICAL MISTAKES WITH PROBLEMATIC SPECIES
You can experiment and make mistakes in a space habitat. Especially biological ones. If the species you are working with interact in strange ways or some microbe evolves that's a problem in worst case, you scrub its atmosphere and soil and start again. You can never start again with a planet if you make a mistake. You just have to move on and hope you find a solution - but what if you have taken a wrong turn and there is no solution to your problem?
Maybe after a few centuries of space habitats we'll know enough to decide to terraform or paraterraform a planet.
There is no hurry.
NOT A PRIORITY ANYWAY TO BE INTERPLANETARY - EARTH AS OPTIMAL PLACE FOR HUMANS IN OUR SOLAR SYSTEM FOR THE FORESEEABLE FUTURE
I don't think it should be our priority to become an interplanetary species either, don't share that premiss. Because whatever happens, the Earth will remain the most habitable place in our solar system.
There is no way we can mess it up to make it less habitable than Mars, and no natural disaster can do that either (not even the 10 km asteroid at the end of the dinosaur era made Earth anything like as uninhabitable as Mars - for that it would need to lose all its oceans and most of its atmosphere for starters).
So almost any solution we find that works in space will work far better as a way to build habitats on the Earth. About the only exceptions there I can think of are the likes of large scale thin film mirrors for solar power - and anything that depends on mining resources that occur as much richer ores in space - but with far future technology it probably won't be difficult to return those materials to the Earth.
So, for better or for worse, we depend on Earth and our priority instead should be to save and protect our Earth, there is no point in trying to escape from it.
CAN'T TELL WHAT WILL HELP THE INHABITANTS OF EARTH 500 MILLION YEARS FROM NOW WHEN THEY MAY NEED TO GO INTERPLANETARY
About 500 million years from now, yes, Earth will probably become increasingly uninhabitable. Whatever species is living on Earth then will need to become interplanetary if it wants to survive. But we don't need to. Also, it is hard to see how anything much we can do now would help those beings half a billion years from now. We don't even know if they would be oxygen breathers, might be that they want an atmosphere of hydrogen sulfide or methane for instance. It's rather improbable that there will still be biologically identical humans by then.
So - I see these settlements as primarily for exploration, adventure, tourism etc rather than as a way to make our species interplanetary. I don't see any value in attempting that at this present time, though it is great to work on the ideas just in case they are useful for whatever species needs it 500 million years from now - but perhaps more so - because the ideas can also help us with smaller scale habitats, and may help us understand exoplanets - and maybe some day we may want to transform a planet, but not necessarily for colonization purposes.
AVAILABLE LAND SURFACE AREA OF A THOUSAND PLANETS
As for available surface area, then in the asteroid belt alone there is enough material for building habitats with living area of 1000 times the land surface of the Earth. So we aren't going to run out of it any time soon.
Asteroid Resources Could Create Space Habs For Trillions; Land Area Of A Thousand Earths
This is even without the planetary protection issues.
Except for Earth that is, obviously habitable for us.
VALUE OF MOON, VENUS UPPER ATMOSPHERE
The Moon seems useful because it is so easy to get to from Earth. We could usefully have settlements, for instance in lunar lava tube caves, or at its poles. Because the cave habitats are already formed, cosmic radiation shielding, if they exist, and because you can get back to Earth in a couple of days in an emergency.
But Mars, I don't see as being of value there. If it is, needs to be for some reason like that. I think if you look into it in detail, it's not the obvious place to start at least.
The upper Venus atmosphere does have an advantage over space stations however. Permits far lighter weight construction because pressure is equalized inside and out. Radiation shielding. And can go out of doors with just an air breather and acid protection, but no bulky spacesuit needed.
Whether that's enough advantage to make it preferable to a space station, I don't know. Might be. You'd need some good reason though for living in the Venus atmosphere. Because Earth would still be a far better place to build a home.
MARS OF MOST INTEREST FOR SEARCH FOR LIFE - BUT IF THAT IS YOUR PRIORITY - LAST THING YOU WANT IS TO LAND HUMANS THERE RIGHT AWAY
As for Mars main reason for living there would be to study Mars and find out about whether there is life there or not. But if that is your priority, then the last thing you want to do is to land humans there, until you know what effect that would have on life there.
So for Mars, I see it a case of finding if there is any life there first, or what else there is there, and leaving any decisions about whether to send humans there or not for later once we know more about the planet.
And if we ever do introduce life to Mars - if it was as uninhabitable for Earth life as the Moon, no big deal. There is no problem bringing life to the Moon, because there are no habitats and no way for it to spread - at most you get local contamination which you'd avoid close to regions where the scientists are studying organics on Mars (e.g. near ice deposits).
But if Mars does have places where Earth life could reproduce - and if that life can spread in the dust storms or any other way - well as well as making sure we thoroughly understand Mars potential habitats first, and what there is there already, if anything - better to make our mistakes in space stations first before we think about possibly introducing new life irreversibly to Mars.
Hopefully this gives some things to think over - we so often here the case for planetary surfaces these days, but there is a strong case for space station type habitats - the scientists who designed the Stanford Torus and the O'Neil Cylinders had good reasons for favouring that approach.
RESEARCH SETTLEMENTS COULD STUDY MARS FROM ORBITAL HABITATS OR FROM DEIMOS AND PHOBOS
With humans in orbit around Mars or on its moons, they could explore the surface with telepresence - and actually experience Mars more directly than if you were there in person in a spacesuit. So that includes tourists, if that happens - much better experience of exploring the Valles Marineres, say, from orbit via telepresence using avatars on the surface.
And everything you see is automatically streamed as HD binocular vision, and also haptic feedback, so others can then look at what you saw, just as you did. And any accidents will only damage repairable machines on Mars, not kill humans. And you can control rovers anywhere on the planet, jump from one to another, you see almost the entire planet at one point or another (twice a day in some orbits) - and Mars looks great from orbit, the continually changing views as you sweep around Mars. On the surface you'd be trapped in one place and liable to see nothing at all during dust storms.
So - there are many reasons for supposing our equivalent of Antarctic bases, for Mars, if we do send humans there, will be in orbit or on Phobos or Deimos.
See my Telerobotic Avatars On Mars With Super-Powers ("Teleporting" from orbit) - Search For Life - And Long Term Exploitation
and To Explore Mars With Likes Of Occulus Rift & Virtuix Omni - From Mars Capture Orbit, Phobos Or Deimos
See also Trouble With Terraforming Mars
and Imagined Colours Of Future Mars - What Happens If We Treat A Planet As A Giant Petri Dish?
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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