Fastest Way to Expand Living Space on Mars

[sanman]

Okay, but how are you going to get all that sand and rock to stick to your dome without having to move a mountain of material?

Regarding the sand and rock reducing the weight of the gas envelope, I'd think that the added weight of the sand and rock would be yet another load that your envelope would have to be strengthened against.

I understand that sand and rock can shield you against radiation, but how thick a layer would you need to cover up with in order to guard against a meteor strike, especially if it's loose sand and rock?

It just sounds like this structure would not be a rigid shell. In which case, why not minimize the mechanical loads on it, and just use it for simple greenhouse purposes?

[guckyfan]

Why would you protect from meteorites?

The Mars atmosphere will adequately shield from micrometeorites. And you don't shield from meteorites on earth. It's just one of those risks.

A dome might be built like the ancient builders of cathedrals did. Form a dome of sand and lay formed blocks of stone or concrete over it. The completed dome will be strong enough for a big load even if unpressurized. Then roemove the sand from inside and pile enough dirt over it to withstand the airpressure when the structure is pressurized. That's probably 10m or more as even a cast iron dome would need to be several meters thick or it is lifted from its foundation by air pressure.

[Andrew_W]

Okay, but how are you going to get all that sand and rock to stick to your dome without having to move a mountain of material?

I'd go for a wider, lower dome, not a full hemisphere, and it's in a crater to retain the material.

Regarding the sand and rock reducing the weight of the gas envelope, I'd think that the added weight of the sand and rock would be yet another load that your envelope would have to be strengthened against.

I think that's a bit like arguing that sticking an inner tube inside a tire will result in the need for a heavier inner tube to resist the pressure exerted on it by the tire.

I understand that sand and rock can shield you against radiation, but how thick a layer would you need to cover up with in order to guard against a meteor strike, especially if it's loose sand and rock?

See guckyfan's comment

It just sounds like this structure would not be a rigid shell. In which case, why not minimize the mechanical loads on it, and just use it for simple greenhouse purposes?

See title of thread.

[sanman]

Why would you protect from meteorites?

Because they could puncture your dome, which could be fatal to the inhabitants.

The Mars atmosphere will adequately shield from micrometeorites. And you don't shield from meteorites on earth. It's just one of those risks.

But on Earth there's no real risk of asphyxiating if a meteor punches a whole in your roof.

A dome might be built like the ancient builders of cathedrals did. Form a dome of sand and lay formed blocks of stone or concrete over it. The completed dome will be strong enough for a big load even if unpressurized. Then roemove the sand from inside and pile enough dirt over it to withstand the airpressure when the structure is pressurized. That's probably 10m or more as even a cast iron dome would need to be several meters thick or it is lifted from its foundation by air pressure.

But how airtight would this solution likely be?

By the same token you could inflate a dome or form, and pour cement directly over it to make a shell that way.

Anyway, consider that an unshielded dome could be a quick way to do large-scale crop cultivation, to scale up food output on Mars. It would require less work to erect and would be less safe, but crops don't warrant the same safeguards that people do. You could also have livestock in there, to supply meat and dairy.

[sanman]

I think that's a bit like arguing that sticking an inner tube inside a tire will result in the need for a heavier inner tube to resist the pressure exerted on it by the tire.

Not sure I agree - the inner tube is meant to oppose the compressive load of the vehicle, relative to which the tire's compressive load is minimal.

A Mars dome would be experiencing a decompression load from the atmosphere within. If you put your rocks on top to oppose this then you have a compressive load from above, but this load won't be homogenous and symmetric like a fluid. There's going to be unevenness that puts a further strain on your envelope, instead of perfectly balancing the air pressure.

It just sounds like this structure would not be a rigid shell. In which case, why not minimize the mechanical loads on it, and just use it for simple greenhouse purposes?

See title of thread.

Well, greenhouses or crop fields are living spaces too - just not for people primarily - and they can provide a valuable resource buffer to a colony, by scaling up food cultivation. Could be a lot cheaper on scalability than growing everything hydroponically.

[guckyfan]

Why would you protect from meteorites?

Because they could puncture your dome, which could be fatal to the inhabitants.

The Mars atmosphere will adequately shield from micrometeorites. And you don't shield from meteorites on earth. It's just one of those risks.

But on Earth there's no real risk of asphyxiating if a meteor punches a whole in your roof.

The likelihood for anything large enough to penetrate the martian atmosphere is just too small to be considered a design issue.

But how airtight would this solution likely be?

It will need an airtight liner for sure. Concerns for uneven pressure of the dirt mass are probably justified. I would prefere some inflated bubble that self contains the forces of airpressure. Especially for greenhouses that would be needed.

By the same token you could inflate a dome or form, and pour cement directly over it to make a shell that way.

Anyway, consider that an unshielded dome could be a quick way to do large-scale crop cultivation, to scale up food output on Mars. It would require less work to erect and would be less safe, but crops don't warrant the same safeguards that people do. You could also have livestock in there, to supply meat and dairy.

The problem with bubbles is that the forces that need to be contained are enormous. It will not be cheap or simple to achieve. I still see it a lot easier than caves plus solar arrays plus LED-lights. Especially if the plants are grown under much lower pressure than the human habitats will need.

[sanman]

Andrew_W,

Maybe your idea would benefit from using a deeper crater, and also using a different breathing gas mixture that's much heavier than air - like a mixture of oxygen and the infamous sulfur hexafluoride. This heavier mixture could stay contained inside the deep crater walls, and you can have your shallow lid across the top like you said.

Of course you know the ladies are going to sound like the guys, but you may have more fun para-sailing:

[Andrew_W]

I think that's a bit like arguing that sticking an inner tube inside a tire will result in the need for a heavier inner tube to resist the pressure exerted on it by the tire.

Not sure I agree - the inner tube is meant to oppose the compressive load of the vehicle, relative to which the tire's compressive load is minimal.

A Mars dome would be experiencing a decompression load from the atmosphere within. If you put your rocks on top to oppose this then you have a compressive load from above, but this load won't be homogenous and symmetric like a fluid. There's going to be unevenness that puts a further strain on your envelope, instead of perfectly balancing the air pressure.

It just sounds like this structure would not be a rigid shell. In which case, why not minimize the mechanical loads on it, and just use it for simple greenhouse purposes?

See title of thread.

Well, greenhouses or crop fields are living spaces too - just not for people primarily - and they can provide a valuable resource buffer to a colony, by scaling up food cultivation. Could be a lot cheaper on scalability than growing everything hydroponically.

There are two ways to ensure stability:
1. enough tensile strength in the dome to ensure the integrity of the dome where the weight of material above is slightly less, perhaps the dome can withstand an internal pressure of just 1PSI with no material on top, so as long as you're within 1 pound (Martian weight) of the ideal of material over each square inch the dome will support the weight above without blowing out.

2. under pressurize the dome and have the material above able to support itself to the degree of this under pressure, which means sintering it or incorporating ice, or cement, whatever is cheapest.

Or a combination of 1 and 2.

[Andrew_W]

Sulfur hexafluoride is about 5 times as dense as air, if you have a dome that's 10 meters floor to roof with an atmosphere at STP on the floor, the pressure a sulfur hexafluoride atmosphere would exert on the roof would be 10,000 - 10 x 6.12 = 9,938.8 kg/m^2, Air would exert a pressure of 10,000 - 10 x 1.225 = 9,987.7kg/m^2.

Not enough gain to justify the effort.

Edit: Actually the difference is even less than that, I didn't allow for the lower Martian gravity.

[gbaikie]

To summarize. The fastest [and cheapest] way to expand living space on Mars, would be have a NASA a manned exploration of Mars.

A exploration of Mars [with crew on Mars one can increase the amount robotic mission to Mars, and each of these robotic by having human presence will allow significant increase in their capability].
Or one could increase the capability of 1 billion dollar robot so it can do a much as 2 billion dollar robot.

One many purposes of NASA Manned Mar program would be to explore Mars to find faster ways of expanding living space on Mars. So that in some future point, one could plan to utilize these discoveries.

And since some people think finding life on Mars could be important these two purposes would be more or less aligned. Where you could look for life would areas in which sheltered this life. So finding caves is important for both these objectives. Another place to look for life is around water. And water may also be associated with caves.

How do do seal a cave entrance? Shape door way area. Drill hole into the rock, and using anchor bolts attach a frame. And from the frame, everything else is attached. The frame in addition to bolted using tensional strength of anchors, the frame can also held into place using compressional force. One could use screws/bolts to create such compression load. Or one can make the frame so it's very sturdier.
The frame can very solidly attached to rock wall, and still have air gaps between steel frame and the rock. But such gaps can be easily sealed- such as epoxy foam. But there types of sealants usable- mortar/stucco,
many possible kind of glue/adhesion/chalking/sealant/resin or even common clayish mud or if it's always cold enough- water ice.
What is mainly important is that the rock or the frame don't move from when it's being pressured, and these components will be taking the important load.
The harder part is the rest of cave not being airtight.
And also you want airlock, so instead have two steel frame separated by say 10 feet and both attached to rock and both frames bolted to each other.
And of course if found large amount of easily accessible water- from a well, lake, glacier, whatever. With large amount water one use it's transparency and it's radiation shielding properties for numerous ways mentioned in this thread.

But a point is that for exploration, one may mostly rely on prefab structures, and beneficial types of local terrain. Having lots accessible mars sand that one partially bury these prefab structure, might be useful. But the exploration it's doesn't need fast and cheap way to expand living space at the moment manned mars exploration begins.
Once you on Mars and if want to move to different location or one need larger crews on Mars, what has been already explored could indicate where and how to do this.

[alexterrell]

How's this for an alternative:
1. Find a suitable crater in a suitable location - easier than locating a suitable cave in a suitable location.
2. Inflate, to low pressure, a gas proof liner in the bottom of it.
3. Throw fine sand (screened to remove larger rocks) over the liner.
4. once the liner is adequately protected by sand you can start chucking in larger rocks.
5. Slowly increase the pressure to match the increasing weight on the liner.
6. move in furniture.

This could work, but I wouldn't like a structure that can't withstand being depressurised. One soultion is that the "furniture" includes buildings that can support the roof.

Also the gas proof liner has to cover the walls and floor - or these can be bitumen sealed later.

For living accommodation, I still prefer the cut and cover method. It's more complex but can mostly be built by machines - overhead crane scooping out regolith, which is then processed for materials, with another verhead crane assembling the steel structure. See picture for a 15m by 15m structure, and extend this to any length you like (though for redundency, after about 500m you'd start another one).

[Russel]

I'm not fond of non rigid structures balancing air pressure within and weight of soil above. One effect you'll get is a runaway instability where a small deficit in mass over one spot will cause that part of the liner to rise, as it does the soil above gradually displaces, and you basically get a bubble blow out.

Oh and btw, regarding rigid natural structures or man made cavities. You don't have to apply rigid gas tight membranes or pre-make them to form. A better way is to spray on a material. Given you only need a thin membrane there's an argument for importing the material. A suitable material would be ordinary polyethylene. Just heat and spray.

[alexterrell]

I'm not fond of non rigid structures balancing air pressure within and weight of soil above. One effect you'll get is a runaway instability where a small deficit in mass over one spot will cause that part of the liner to rise, as it does the soil above gradually displaces, and you basically get a bubble blow out.

I think The Health and Safety Executive will say the structure must remain in event of Zero Air pressure inside, and zero soil pressure outside.

There may be exceptions for:
- structures not normally inhabited - for example a crop area
- where the inhabitants are protected by secondary structures. For example, each "dwelling" is presurisable, but the "village" is covered by such a layer. As long as the dwelling can survive a pressure failure.

Oh and btw, regarding rigid natural structures or man made cavities. You don't have to apply rigid gas tight membranes or pre-make them to form. A better way is to spray on a material. Given you only need a thin membrane there's an argument for importing the material. A suitable material would be ordinary polyethylene. Just heat and spray.

Nice idea. I think the membrane would have to be quite thick - perhaps 10mm - or you have to prepare the walls - sanding down. I suspect your painter/decorator will know more about this than NASA.

In any event, the spray on mass could be greater than that of an inflatable.

But some sort of plastic could be manufactured on Mars. Perhaps something like Bitumen would be better than Polyethylene - it's used for water proofing roofs and exterior walls on Earth. Polyethylene is used in sheets. 

[colbourne]

The spray on liquid , could be something as simple as water. As long as the pressure is high enough in the tunnel to stop sublimation. Water should be easily available if the base is near a patch of Martian ice. There are probably additives that could be added to the water to make the ice more sticky and damage resistant.
Bases could also be built inside the ice caps or other large bodies of ice.

[alexterrell]

I would assume the cave is going to have 10s of metres of regolith protection? That will also make for a good insulator. Water would melt and evapourate once the base has warmed up the cave.

If you have time and power, how about laser fuse the walls and floor? Several months with a 50KW laser?

[guckyfan]

I really do not understand how the idea to use water in building on Mars. I don't see using a material that is liquid in the temperaturerange suitable for humans for building human habitats.

YMMV though.

[KelvinZero]

We are talking about building outer walls exposed to martian temperatures, not toilet seats

You need a good heat insulator between you and the ice, but that would be very light weight, eg a few feet of bubblewrap. After that it is straight physics. An engineer will run the numbers and know if there is a risk of the ice approaching a temperature at which it loses strength. Remember we are talking about a world that snows carbon dioxide so there is quite a safety margin.

I personally favor not building of ice but into it. A thirty meter thickness seems a nice safe round figure if we are trusting our lives to entirely insitu construction, plus the other advantages of earth pressure, radiation protection, liquid water, low wear on tunneling equipment and so on.

[A_M_Swallow]

I really do not understand how the idea to use water in building on Mars. I don't see using a material that is liquid in the temperaturerange suitable for humans for building human habitats.

YMMV though.

It is easier to spay liquids than solids.  For a solid surface you need something that freezes at Martian temperatures.

I can see water/ice working below the floor but need convincing that it is safe for roofs since heat rises.

[gbaikie]

In terms of topic:  Fastest Way to Expand Living Space on Mars.

You have two separate topics. One would have to do with exploration of Mars and the other would have to do with settlements and commercialization of Mars.
It seems to me that to make a living on Mars, you need relatively cheap
living space and this is has to do with fastest way to expand living space on Mars.

Or the answer to the "Fastest Way to Expand Living Space on Mars" could be terraforming Mars. If you thought a project of global terraforming was workable- which I don't. I think we will terraform Mars in sense that human have been terraforming earth for thousands of years or perhaps more significantly within the last century or two. Or life [rather than human] has been terraforming Earth for billions of years.

In terms of exploration of Mars and living space. First you don't need a lot of cubic meters of living space as human population might be less than
20 people. As NASA program it's limited due to budget, but seems the whole purpose of NASA exploration of Mars is related to question of future human settlement of Mars.

Let's look at difference between Mars and the Moon.
It seems to me the main thing about the Moon is it is the gateway to the solar system. It's the question of whether the Moon has minable water [or some means to make rocket fuel] which is a critical aspect of the Moon. One could say the Moon is about industrialization and Mars is about farming as broad and loose comparison.
So if key aspect of the Moon is minable lunar water, a key aspect of Mars will involve "Fastest Way to Expand Living Space".
To make the cheapest greenhouse on Mars could be fairly significant-
or living space includes living space for plants.

And I think the idea of NASA mining lunar water and NASA grow crops of Mars astronauts- NASA growing a human population on Mars- are similarly
foolish. NASA should focus on exploration of space. NASA should explore the Moon and explore Mars.
And the key aspect of NASA exploration [broadly and in general] is related to the problem of lowering the cost of people on Earth getting out of Earth's gravity well.
And is related to creating markets in space.
And markets are related to finding something of near term value to people living on Earth.
There is probably nothing as valuable to all people living on Earth, has having cheap access to space. Which essentially means that the costs of leaving Earth is not insurmountable barrier to doing things in space which have value. And we have already achieved this in a limited way, as the cost of putting satellites in Earth orbit is not insurmountable barrier to gaining value from the use of satellites. We already have a satellite market.
We need a rocket fuel market in space. And we need other markets in space.
With rocket fuel market in space, NASA can explore Mars in through fashion rather than the flags and footprint fashion. And we need a comprehensive exploration of Mars before human settlement of Mars.

The idea of private effort at Mars settlements [ie, Mars One] is very similar to flags and footprints- it's a stunt. And such a stunt, might or might not help towards achieving Mars exploration. But it's exploration which is key to human settlements of Mars.
Stunts are all about PR, it may be that private efforts of a flag and footprint Mars might do a better job with it's gained PR than NASA could. But my point is there is this need of exploration of Mars before real settlements on Mars are possible.
And there needs to be more markets in space, before real settlements on Mars is possible.

[sanman]

Or the answer to the "Fastest Way to Expand Living Space on Mars" could be terraforming Mars. If you thought a project of global terraforming was workable- which I don't. I think we will terraform Mars in sense that human have been terraforming earth for thousands of years or perhaps more significantly within the last century or two. Or life [rather than human] has been terraforming Earth for billions of years.

Well, we don't have to use gradual or subtle means to terraform Mars. Just start dropping large objects from the sky down on it - I'm thinking large ammonia asteroids - and that could work a lot faster than greenhouse gases and CFCs.

But anyway, terraforming should probably come later, after we have adequately explored the planet to know enough about what we should do.