Construction technology for Mars?

Oldfart1939 · 2018-03-08 15:06:57

Robert-

In my double wall construction model above, I suggested regolith for 2 reasons: (1) immediate availability, (2) attenuation of radiation. An additional insulation layer could be added inside the brick and subsequently covered by drywall.

JoshNH4H · 2018-03-08 15:11:41

IanM wrote:

Hey Josh,
Thanks for your commentary. I neglected the tension within the brick wall and only focused on the pressure gradient that was perpendicular to the wall. The acceleration due to the pressure gradient is given by https://www.shodor.org/os411/courses/_m … index.html (I didn't use the calculator, just its equation), and I essentially saw the wall as simply a way to increase the distance between the inside and outside and thus reduce the gradient to acceptable levels. The 2 psi figure I got from page 10 because I mistakenly thought that is what transverse load meant, but that was essentially my method.
Given that mistake and your inclusion of tension I believe your number is more reasonable, but we do ultimately agree that brick is garbage for exterior walls. If we really wanted it for aesthetic reasons, I would suggest we make a load-bearing wall out of a much better material and contain all pressure within it, and then lay the brick facade immediately outside it where there's no pressure gradient.

I'm glad we've cleared this up. In the future, the Wikipedia article on pressure vessels might point you in a better way to compute required thickness, particularly this section.

I remember back in the day I used to compute the required thickness by dividing the internal pressure by the tensile strength. I had to go back and fix a whole bunch of stuff when I figured out the mistake!

SpaceNut · 2018-03-08 18:35:26

So far all of the conversation has revolved around insitu material use with tonnes of equipment and power coming out the gazooo but to get there with a mars direct or minimal start will require a different thought process for building.

The Mars Direct is smallparts or pieces simular to a dragon, cygnus, or a bigelow inflateable for use will plenty of solar panels being used. This mean a prestaging of cargo in a mars created cargo lander. The thoughts I have for something that is near to a design for a cargo lander would couple the Dragons supper draco engine, storable fuels into a new propulsion section that would be attached to a cygnus for a powered landing. The cygnus would double as a construction item for making a surface habitat by unassembling it from the landing section and placing it on the ground. Couple as many as are available to form the new station on mars covering it with regolith. We still can use the mars concrete and any other insitu made materials to aid in hardening of the facility for manned use.

The elon musk BFR was to land 2 cargo units and a crewed vehicle to which I would go with recycling the unused tanks of the cargo landing into useable room once airlocks are added. This can be done with them still in the ship or via removal and burying just as before.
The second ship for creating the refueling station would be left along for that purpose.

RobertDyck · 2018-03-08 19:04:57

Josh, I'm not saying a Mars habitat *HAS TO* be brick, I'm saying it's an option. And a low cost one. We can experiment with regolith simulant on Earth. We know the composition from sites where we sent rovers. And I'm not saying the site is fictional. The Mars Homestead Project actually chose a specific site. The shape of the hill is directly from orbiter imagery. It's a mid-latitude location where glaciers in the sides of canyons have been identified. Of course my posts here have argued for a location that is flatter, to make landing safer. And closer to the equator: warmer and more consistent sunlight summer/winter. Members on this forum convinced me that the frozen pack ice is a great site. That's a part of Elysium Planitia, specifically Cerberus Fossae. Is there a suitable hill there?

Also realize any site for a human base must have plenty of water. If it's a glacier in the side of a canyon or a frozen sea, there's enough to soak any dirt packed against the brick. That wouldn't just make it saturated clay, it would be permafrost.

Oldfart1939 · 2018-03-08 19:39:15

My idea for brick is NOT the normal stuff we are familiar with here on Earth. I like using regolith blended with ISRU monomeric material, of a variety of types. These would be probably 5x the size of Earth bricks that would yield a wall ~ 5x thicker and heavier. This regolith based wall would be ~ 30 cm thick and contain a high %age of carbon based polymer. They would be "glued" together with a slow setting epoxy resin and form a virtually gas-tight structure. Yeah, this is not for the first settlement on Mars, but could provide an early industry on the planet and EMPLOYMENT!

JoshNH4H · 2018-03-08 20:01:22

RobertDyck wrote:

Josh, I'm not saying a Mars habitat *HAS TO* be brick, I'm saying it's an option. And a low cost one. We can experiment with regolith simulant on Earth. We know the composition from sites where we sent rovers. And I'm not saying the site is fictional. The Mars Homestead Project actually chose a specific site. The shape of the hill is directly from orbiter imagery. It's a mid-latitude location where glaciers in the sides of canyons have been identified. Of course my posts here have argued for a location that is flatter, to make landing safer. And closer to the equator: warmer and more consistent sunlight summer/winter. Members on this forum convinced me that the frozen pack ice is a great site. That's a part of Elysium Planitia, specifically Cerberus Fossae. Is there a suitable hill there?
Also realize any site for a human base must have plenty of water. If it's a glacier in the side of a canyon or a frozen sea, there's enough to soak any dirt packed against the brick. That wouldn't just make it saturated clay, it would be permafrost.

I don't think it is an option, at least not as an element that bears any load other than compressive ones (meaning no shear, bending, or tensile forces of any substantial magnitude!)

Depending on how well-insulated your habitat is, moisture in the surrounding dirt actually has the potential to make your problems worse. The lateral earth pressurization scheme won't work at all if the ice/dirt mixture forms a solid block that can't subside into equilibrium. At that point, you might suggest encasing it completely and directly in ice, at which point I would have to ask why you are using something brittle and weak (plus melt-able under the wrong conditions) like ice as a structural material.

JoshNH4H · 2018-03-08 20:10:04

Oldfart1939 wrote:

My idea for brick is NOT the normal stuff we are familiar with here on Earth. I like using regolith blended with ISRU monomeric material, of a variety of types. These would be probably 5x the size of Earth bricks that would yield a wall ~ 5x thicker and heavier. This regolith based wall would be ~ 30 cm thick and contain a high %age of carbon based polymer. They would be "glued" together with a slow setting epoxy resin and form a virtually gas-tight structure. Yeah, this is not for the first settlement on Mars, but could provide an early industry on the planet and EMPLOYMENT!

It sounds like you're describing carbon fiber composite?

All of these solutions are fine and good, but regular old dirt on Mars has enough Iron to be considered low-grade ore and the atmosphere is made of Carbon.

Steel is easy to make, strong, and durable. It seems like we might be getting a bit too clever on this one when Steel and Concrete really are quality building materials.

SpaceNut · 2018-03-08 21:08:26

Unless you have paid your tickets cost to mars you probably will not be looking for Employment as youwill already be working for some one already.

Oldfart1939 · 2018-03-08 21:14:59

No, I'm not describing carbon fiber composite. What I'd suggest is a polymer similar in composition to ABS plastic with a large percentage of added regolith. The polymerization could be accomplished or initiated by a small amount of catalytic initiator and then heating these bricks in a mold until dimensionally stable and then kept in a heated room for the polymerization to conclude. Probably 90% regolith with about 10% polymer "binder" added. This is relatively low tech. Should be cheap and has an advantage of being more gas impermeable than brick. Build the wall, then "plaster" the inside with a higher polymer content sealant. What is needed is acrylonitrile and butadiene, both of which can probably be made from atmospheric CO2 and some atmospheric Nitrogen. Styrene can also be obtained from atmospheric CO2. ABS plastics are strong, dimensionally stable, and easy to manufacture.

JoshNH4H · 2018-03-08 21:29:43

Well one of many ways to cook the chicken I guess.

Personally I'm gonna stick with steel

RobertDyck · 2018-03-08 22:24:05

JoshNH4H wrote:

Personally I'm gonna stick with steel

The issue is required ingredients. Opportunity already found hematite concretions. That's ideal iron ore. We can get carbon from the atmosphere. Steel is normally smelted on Earth by burning coke in a furnace starved of oxygen so it produces maximum carbon monoxide. That CO strips oxygen from iron oxide minerals to form CO2, leaving iron metal. Early Greek and Roman techniques didn't heat it enough to melt iron, but that left a lot of impurities that weaken iron. Modern method is hot enough to melt steel, which pools at the bottom of the furnace. Carbon from CO dissolves into molten iron to produce steel. Problem is this dissolves too much carbon, producing steel that's brittle. A Bessemer converter adds oxygen to molten steel, burning off carbon. You have to be careful not to add so much that it oxidizes iron. And don't burn off all carbon, leave some because steel is an alloy of iron and carbon. An alternative is to add hydrogen with CO. Hydrogen burns to form water, which doesn't dissolve in molten steel, it boils off as steam. This adds less carbon to start with. Bottom line, we can make steel on Mars.

The issue is additives to make a grade of steel that remains strong through the temperature fluctuations on Mars. You don't want steel that will become brittle in the cold of a Mars night. It has to handle the diurnal temperature cycle. We discussed this, ironically in a thread about glass. My post is here. My Google search found stainless steel 310 will do it. Problem is it requires significant amounts of chrome, nickel, and a little manganese. You can find them in meteorites, but a base will need a lot of it. Actually, just metal meteorites. Most meteorites are stone or carbonaceous chondrite; the issue is how to tell the difference between such a meteorite and normal Earth rock. A metal meteorite is easy to spot, which is why most people only think of metal ones. There are trace amounts of Cr and Mn in Mars surface soil, but not mine-able concentration. And what about nickel? I read that carbon steel service temperature does not go below -29°C. Carbon Steel A/SA333 Grade 1/6 is rated for -45°C, but it has small quantities of manganese and phosphorus. But again, temperature on Mars at night in summer gets down to -77°C to -80°C, in winter much colder. So you need a truly cold service steel.

IanM · 2018-03-09 00:19:40

NOTE: I noticed and read Josh's link to Wikipedia right after I finished this but before I posted it. After reviewing it this might still be valid as it attempts to describe a pressured stress from one side of the membrane/wall/roof to the other, perpendicular to both σx and σy in the relevant Wikipedia diagram. Apologies in advance if such a thing turns out to be invalid.

Continuing on my previous work and hoping to generalize it, here's an equation for the acceleration of a parcel of fluid due to a pressure gradient from https://courses.eas.ualberta.ca/eas570/pgf.pdf with adapted notation:
a(P)=-∇P/ρ
Where ∇P is the magnitude of the greatest pressure increase at a given point (the so-called pressure gradient, something which might require multivariable calculus to determine but as shown below doesn't in this case) and ρ is the density of the fluid. The negative sign is because fluids want to move from high to low pressure, and thus follow the greatest pressure DECREASE and oppose the gradient. In any case we don't care about that since we're concerned with magnitude and not direction, so taking it out nets:
|a(P)|=∇P/ρ
The keen eye would note that this is an acceleration and we're looking for a force (and eventually pressure, somewhat ironically). Henceforth referring only to scalars, force is acceleration times mass, so we'll need mass. Density is mass over volume, so the mass of a gas is its volume times its density. Taking V for volume we get
F(P)=V∇P
We want a pressure from this, so we take this and divide it by the surface area that's exposed to the Martian atmosphere (so including the walls and roof, but excluding the floor). Giving that as S we get:
p(P)=V∇P/S=V/S*∇P
So we want buildings with low volume to surface area ratios, or equivalently high surface area to volume ratios. According to Wikipedia tetrahedra and cubes have the highest such ratios although that doesn't account for taking out the floor.

The tricky part would in theory be determining ∇P, but for any given piece of wall or roof the air would want to escape to the outside perpendicularly, as that would be the shortest way out. This "collapses" the ∇P into a single-variable derivative relating the change of pressure over the change of distance (i.e., the wall/roof thickness), which change we can assume to be linear (and thus derivative constant). Given internal pressure P and wall/roof thickness t (assuming that it is in fact homogeneous), and assuming the Martian outside is a vacuum, this whole thing simplifies to:
p(P)=V/S*P/t

elderflower · 2018-03-09 09:19:45

The floor is subject to Mars pressure via porosity in the ground. It must be sealed well.

JoshNH4H · 2018-03-09 09:19:48

Hey IanM,

Starting from conclusions and working backwards, we know for sure that there's something wrong here...

IanM wrote:

So we want buildings with low volume to surface area ratios, or equivalently high surface area to volume ratios

...Because this is the opposite of what we've found to be true in real life. You want as high as possible of a surface area-to-volume ratio. That's why balloons and balls are round, ISS modules and rocket fuel tanks are cylindrical, etc.

I believe there are a couple of mistakes in your pressure model, but I want to start by showing how the equation for acceleration of a gas can be derived from Newton's Second Law and the definition of pressure because I think it's cool

We know from Newton that:

a=F/m

The force in this case is generated by a pressure gradient between two points. In order to be truly correct, the following derivation ought to be done using calculus. However, for legibility and comprehensibility I will be representing infinitesimal variables as algebraic ones.

The force of a pressure is as follows:

F=(Ph-Pl)*A

Where Ph is the high pressure, Pl is the low pressure, and A is the relevant area. As we know from the definition of density,

m=ρV

And geometrically, V=A*d (where d is the distance between Ph and Pl). Plugging in, we have:

a=(Ph-Pl)*A/(ρAd)

Which simplifies to:

a=(Ph-Pl)/(d*ρ)

And since (Ph-Pl)/d is the algebraic equivalent to ∇P, we have derived your starting equation. If you wanted to do this correctly, with calculus, you'd simply replace (Ph-Pl) with ∂P, d with ∂x, F with ∂F, m with ∂m, and V with ∂V.

Anyway, as far as I can tell your process is dimensionally correct but otherwise physically wrong. Here are the errors that I can see in your method:

1. You have used an incorrect equation for determining force. The equation you've used effectively assumes that the brunt of the pressure differential is being borne by the gases escaping and accelerating freely, and then is somehow transmitted back into a wall. This is a non-physical (or barely physical) situation. As a hypothetical, consider the stresses on a structure with a slow leak vs. one that does not leak at all. Would you expect them to be radically different? The assumptions underlying your model suggest they should be. In reality, even escaping gases experience so much friction on the way out that a slow leak barely affects internal pressure at all. The correct equation is F=PA, where F is the total force acting on the walls, P is the pressure differential between inside and outside, and A is the wall area. F and A are both vectors, and are bolded to denote that.

2. You have not modelled the way the forces acting on the wall become structural stresses in the right way. It is true that there is a pressure gradient in the wall, with the full internal pressure acting on the inner surface and almost zero pressure acting on the outer surface. However, this pressure is not the pressure being borne by the structural elements. By drawing a free-body diagram as I have above and how the Wiki article also does you can see the correct way to do so.

Having said all this, it does seem like fun to try to derive P(r), T(r), a(r) and V(r) for a 1 atm vent exposed to vacuum. That's a derivation for another time though, I think.

Anyway, yeah, use the equations on Wikipedia because those are right. A cool trick for compound structures is that you can use the effective local radius of curvature to compute the local tensile stress. Incidentally that is why completely uncurved structures are no good (such as each wall of a square building) because their radii of curvature are effectively infinite and the force is also therefore effectively infinite. (What happens IRL is that instead of dealing with pure tensile loading you have a situation with huge bending stresses that lead to deformation and/or failure).

Terraformer · 2018-03-09 11:42:12

I read that carbon steel service temperature does not go below -29°C. Carbon Steel A/SA333 Grade 1/6 is rated for -45°C, but it has small quantities of manganese and phosphorus. But again, temperature on Mars at night in summer gets down to -77°C to -80°C, in winter much colder. So you need a truly cold service steel.

Presumably the hab won't get down to this, so could we just insulate the outside of it? Have a thick insulating outer layer, and put the pressure vessel inside that?

Void · 2018-03-09 13:45:26

As I see it there are several easier building methods that come to mind.
1) Sandstone Caves, (Mt. Sharp) and also cutting sandstone blocks to build unpressurized buildings above ground.
2) Underwater habitats, under water, water under ice, ice under a mechanical protective layer.
3) Double domes under ice. That is if you really want to be grand, build a enormous double dome under a polar ice cap, using the ice as counter pressure. Then of course however, you must vent the heat accumulated between the two domes to the outside, to eliminate melting of your counter pressure ice. And if less ambitious do a similar thing under the slabs of ice at mid latitude. Maybe 100 feet high.
4) Lava Tubes afford some protection but will also require structures build.

These are the more easy things.

I do appreciate that you guys are trying to figure out how to build when easier is not available.

There will be cases where a structure is needed, but easier is not available.

Void · 2018-03-09 18:19:35

Well, I must have stunk things up. Everyone left.

Well I recalled reading about the idea of using fiberglass on Mars, so I searched.
https://gizmodo.com/a-region-on-mars-ca … 1737029391
Quote:

Design
A Region on Mars Called Silica Valley Could Help Us Build Fiberglass Space Habitats
NASA has spent the past few years asking architects, engineers, and designers outside of the space industry to think about habitat-building on the Red Planet–in part through competitions like the 3D-Printed Habitat Challenge.
The competition, which wrapped up this fall, asked designers to imagine how found materials on the surface of Mars could be used to create structures with large-scale 3D printing. Ultimately, a design that used water to print igloo-style ice habitats won out. But there were dozens of finalists worth looking at, and this week MIT’s architecture school published a closer look at their own finalist entry.

Their proposal, called Ouroboros, isn’t remarkable for the design of the habitat itself: Their inflatable toroid-shaped dwelling is similar to ideas NASA has been kicking around for years. What’s really interesting about their proposal is how they proposed building it–and from what materials. The team of architects, along with engineering students, came up with the idea of weaving a super-strong fabric that could be inflated using what they could find on Mars’ surface and atmosphere.
They focused in on a region of Mars called Silica Valley–where the Spirit Rover detected that the soil was as much as 60 percent silica. Back in 2007, when NASA announced the discovery of the area, it speculated that the “patch of bright-toned soil” was “so rich in silica that scientists propose water must have been involved in concentrating it,” a hypothesis that has sounds a lot more plausible in light of NASA’s recent announcement about water on Mars.
Silica, of course, is one of the raw materials needed to make glass, which could be extruded in its molten form, creating threads of fiberglass to be “woven” using a project-specific loom. That fiberglass would make a strong, light exoskeleton for the dwelling, though the team also knew they would need some form of air-tight plastic to ensure a pressurization.
“We noticed that the atmospheric and soil composition contained the necessary compounds to make thermoplastics,” says Caitlin Meuller, an assistant professor of building technology, in a video about the project. A group of engineering students came up with the idea of creating plastics using those compounds by “synthesizing the polypropylene needed to make the thermoplastic composite form hydrogen and carbon dioxide in the Martian atmosphere.” That thermoplastic would be woven with the fiberglass and together, heated until they created a bonded structure.
The project ended up not being chosen as a winner, but it’s a great example of the kind of thinking about Mars that NASA is hoping to see more of–in fact, when this competition wrapped up this month, the agency launched a second challenge focused specifically on using Martian soil and rocks for modular construction.

Interesting the materials they claim can be made on Mars.

You could use basalt to make mineral wool, as an alternative.

This is also interesting:
https://www.popularmechanics.com/space/ … an-colony/

If resin could be made, then it might also be useful to make fake wood, by gluing dried reeds together while compressing it into "Boards". (We talked about that elsewhere).

I'm Done.

Last edited by Void (2018-03-09 18:27:59)

Void · 2018-03-09 21:22:27

Oh well I guess this is on topic:
https://en.wikipedia.org/wiki/Martian_polar_ice_caps
Quote:

The caps at both poles consist primarily of water ice. Frozen carbon dioxide accumulates as a comparatively thin layer about one metre thick on the north cap in the northern winter, while the south cap has a permanent dry ice cover about 8 m thick.[4] The northern polar cap has a diameter of about 1000 km during the northern Mars summer,[5] and contains about 1.6 million cubic km of ice, which if spread evenly on the cap would be 2 km thick.[6] (This compares to a volume of 2.85 million cubic km (km3) for the Greenland ice sheet.) The southern polar cap has a diameter of 350 km and a thickness of 3 km.[7] The total volume of ice in the south polar cap plus the adjacent layered deposits has also been estimated at 1.6 million cubic km.[8] Both polar caps show spiral troughs, which recent analysis of SHARAD ice penetrating radar has shown are a result of roughly perpendicular katabatic winds that spiral due to the Coriolis Effect.[9][10]

I am thinking of the double vaulted domes under the ice caps. I would expect that they would have connecting beams that connected from the inside of the outer dome to the outside of the inner dome.

And I am thinking that if you could somehow do a heatpump thing you might draw heat out of the space between the two domes, and push it into the insides of the inner dome. Eventually, though I suppose you would want to dispose of waste heat.

I am thinking that this is a good situation for nuclear power. Giant domes and Nuclear power under the ice caps. Or more humbly under say 200 foot deep ice slabs at mid latitudes.

So, in the assessment of Mars, if it turns out that it will be a very distant possibility to terraform Mars to a suitable pressure of atmosphere, then my choice would be to plan to build giant vaults under the ice caps, and also to provide ice covered canals to bring water to reservoirs at lower latitudes.

We might still hope to get the atmospheric pressure up to at least 70 mb, so that some type of rugged biosphere could be in operation on some of the outside soil areas.

At 70 mb, it may be that open water could exist in places, although 70 mb would also be somewhat protective of an ice covering without mechanical protective devices.

Inside the domes, lots of chemosynthesis, but also perhaps apple orchards under artificial lights, and similarly crops.

Crops under artificial lights are being contemplated here on Earth primarily for urban situation, so why should we be shy about considering it for Mars? And inside these domes then skyscrapers, a city.

Seriously what do you think?

OK, I'm done.

Last edited by Void (2018-03-09 21:32:38)

Void · 2018-03-10 14:04:12

One construction technique could be to carve upwards in the ice from bedrock.

Build the two walls as you go. Also pour a whetted mixture of Mineral Wool or Fiberglass in the zone outside the outer wall and let it freeze.

Then you could depend on some of the strength of your double dome to be provided by this frozen fiber wall.

How thick? Well I guess that depends on what you need for strength, and how much mineral wool or fiberglass you can afford to manufacture.

......

Added later:

I would keep the interior of the double domes filled with ice until the whole double dome project was completed. Then melt it, and send it into a canal to send it to either lower altitudes, or latitudes or both.

An inverse method could be used it high latitudes.

Build the double dome, and then place ice and fiber on top of it, sufficient for your needed counter pressure.

I am hoping that fiber ice will have both tensile and compressive strengths.

But that construction approaches this:

https://www.nasa.gov/feature/langley/a- … red-planet

http://www.dailymail.co.uk/sciencetech/ … -home.html

The point being I guess, if the techniques can be done, then it should be possible to produce enormous pressurized volumes on Mars.

As for agriculture, you must know that I am a proponent of underwater agriculture, both Chemosynthetic, and Photosynthesis.
I also favor robots that present air filled canisters to sunlight under a surface of clear ice.

So then perhaps agriculture inside the domes would be specialty crops, and also to a large degree done to please the inhabitants.

Most food would come from outside the domes.

Last edited by Void (2018-03-10 14:18:54)

JoshNH4H · 2018-03-10 14:16:47

Terraformer wrote:

I read that carbon steel service temperature does not go below -29°C. Carbon Steel A/SA333 Grade 1/6 is rated for -45°C, but it has small quantities of manganese and phosphorus. But again, temperature on Mars at night in summer gets down to -77°C to -80°C, in winter much colder. So you need a truly cold service steel.
Presumably the hab won't get down to this, so could we just insulate the outside of it? Have a thick insulating outer layer, and put the pressure vessel inside that?

This seems pretty reasonable to me. You might put heating elements on the steel during construction as necessary and keep them there as a backup in case of power failure.

You could also use water storage near the outer edge as a way of keeping the temperature above -10C, as the freezing of water will naturally keep the temperature stuck at 0 C for a while if necessary.

The key consideration is that in the case of a total failure (ala Clark's Calamity) the building will also become structurally unsound and will be at a substantial risk of failure until it can be warmed back up towards freezing. You can imagine a world where people survive depressurization and/or a power outage only to be killed by the implosion or explosion of the building where they are sheltering (with damage also being done to neighboring buildings).

Having said that, there are lots of cities with steel skyscrapers where temperatures regularly dip down to -10 C or below. Places like New York, Boston, Pittsburgh (a town so invested in Steel that their NFL team is called the Steelers), Chicago, Montreal, Toronto, St. Paul, Minneapolis, Winnipeg, Edmonton, Oslo, Stockholm, Helsinki, Warsaw, Moscow, Kiev, and Beijing are all places that could conceivably face a more mild version of this problem, although admittedly some more than others (Here in New York we complain to high hell when it gets down to -10, but I imagine up in Winnipeg you call that a balmy summer day). If you look at Wikipedia's list of bridge failures there are definitely a few that were caused in whole or in part by extreme cold temperatures. I have also seen videos where cities like Chicago set their train tracks on fire on purpose in order to prevent them from getting too cold.

The benefits of using steel vs. other materials (like Aluminium, which has a lower service temperature) pretty much go away if you need to use stainless steel. So let's say you want to stick with regular mild carbon steel as your primary building material. Here's some options, off the top of my head, that you might pursue to use it at these lower temperatures.

Heat the steel whenever it might be exposed to Martian ambient temps, insulate really aggressively (good idea regardless) and hope your heat never ever fails. As a fail-safe, have active pressure containment valves that work so long as the regular and backup power supplies are working. Should both main and backup power fail, the valves open and slowly release air to lower the pressure and prevent structural failure. Alternatively, design them to be temperature-based valves that will open if the temperature falls below, for example, -5 C.
Overdesign the structure so that it will not fail even if the steel becomes brittle
Cold roll substantial amounts of basalt fiber into the steel. Basalt fiber maintains its properties at low temperature and will ensure that the steel used maintains a certain amount of strength. This would have to be considered a kind of composite. Before you ask why you wouldn't just use basalt fiber, that's also a great option especially if you need flexible tethers.
Coat the steel in a layer of material that will not become brittle at low temperatures and has a higher coefficient of thermal expansion (I'm thinking Aluminium). This is sort of like a really aggressive version of tempering, a process also used to increase the strength of auto glass. The idea is that if the structural element becomes cold, the outer layer will contract more than the main body of the beam, which will result in tension being carried more by the outer layer than the inner one, while the inner layer is put into compression. The outer layer can also help protect the main body from impacts that can cause brittle failure.

I imagine that, depending on the application, you will see a mixture of all these used (plus others I haven't thought of). You'll also definitely see temperature affecting material choice in some applications.

Good catch.

JoshNH4H · 2018-03-10 14:35:36

Hey Void,

I am not going to say that the things you're suggesting are impossible or unworkable because they certainly are not, but they do require that a lot of attention be paid to the geology of your surroundings.

Natural formations, including ice, are rarely solid and often contain severe fault lines and weaknesses. While buried settlements will reduce the pressure containment requirements of the settlement when the surrounding materials are solid and reliable, this will often not be the case and failure will tend to be catastrophic (i.e., whole settlement explodes).

There are composites that can be made by taking fibers of various kinds (most often cellulose fibers like you'll find in wood and paper but also potentially including things like carbon fiber or basalt fiber) and allowing them to freeze in water. As long as the temperature never approaches freezing the composite will have a comparable strength to other composites.

A big risk with this kind of material is that if exposed to the ambient martian atmosphere the water will slowly sublimate and "rot" away, with a severe loss of strength. They do also tend to be very brittle (low impact resistance) so that's something to watch out for.

Oldfart1939 · 2018-03-10 15:44:07

As much as I like structures built from steel, I suspect that the Mars steel industry will develop more slowly than the Mars polymer industry. I believe that Zubrin may already have the method--or the chemistry defined--for butadiene. Styrene should be equally accessible from the same feedstock: CO2 and H2O. Acrylonitrile may be a step further down the research road, but in principle--doable. ABS plastics hare enormous application in the construction industry on Earth, especially for underground plumbing drain lines. Regolith--especially sandy regolith--would make an ideal "filler" for a binder of ABS monomeric resins. The initiation of polymerization is endothermic, but once started, the reaction is exothermic (generates it's own heat). Could make a helluva lot of polymer bricks in a day, and requires far less infrastructure than a brickyard. Just reiterating my polymer bricks case here.

JoshNH4H · 2018-03-10 17:05:30

Both are important, naturally, but I think Iron will tend to be a cheaper material than polymers. Here's the processes required for making a steel element:

Locate acceptably high quality sources of Iron ore
Mine and pulverize the ore
Electrolyze water to generate Hydrogen
Two possibilities: Use the hydrogen to create CO, then mix the H2 and CO to smelt the Iron ore and collect the steel produced thereby, or smelt with pure Hydrogen and then use the carbonyl process to create pure Iron/mix it with carbon and heat to mix into steel
Form and use the Steel

It's hard to give a comparable list for how you would make polybutadiene, because there are so many different possible synthesis pathways. You can get an idea from this page which I believe was written by our friend RobertDyck. The point is that plastic synthesis has a lot more steps (some of which create large amounts of byproducts) and requires a lot more energy to create a given amount of metal, while polymers also have significantly less strength than metals.

IanM · 2018-03-10 17:46:50

For above-ground settlement I think what at least some of us are looking for is a Quonset hut.
https://en.wikipedia.org/wiki/Quonset_hut
The semicircular cross-section makes it an appropriate pressure vessel (although the flat sides might be somewhat problematic), and its lightweight material should make it rather cheap and quick for a theoretical boomtown to make. They can also last pretty long: many are still in usable condition 70 years after WW2. The main drawback I can find is poor radiation protection: new galvanized steel has an albedo of 0.35 (http://files.pvsyst.com/help/albedo.htm) and dirty steel has one of 0.08, less than even grass. However, if it doesn't adequately protect its inhabitants we could always put regolith on it as Oldfart1939 has so often suggested.

Last edited by IanM (2018-03-10 17:49:45)

GW Johnson · 2018-03-10 18:12:38

If you go check "glassy transition temperatures", I think you will find that almost all polymers have glass transition temperatures higher than Mars ambient at night, even at the equator in summer. Once cooled below that glass transition temperature, these materials are as brittle as a piece of glass here on Earth. They are even more vulnerable to brittle failure soaked cold than carbon steel, and carbon steel is notorious from its use in Siberian gas plants that blew up from gas leaks due to brittle failure.

If metal used at Martian night and winter temperatures, about your only practical material is a 300-series stainless steel. This stuff is the preferred material for Earthly storage of cryogens here on Earth. There's a very good reason for preferring it hands-down, too.

You can use those other materials if you can ALWAYS prevent them from ever soaking out cold. That simply ain't gonna happen during construction on Mars, even if you specify insulation on the outside of the pressure vessel. Some of that practical, real-world stuff is certainly inconvenient, ain't it?

As for pressure vessel wall thicknesses, the equation to use (ONLY for truly round structures, not even ellipsoidal !!!!!) is a version of Barlow's equation (way over a century old for pipe stress problems): P ID = 2 tw s, where P is the gauge pressure inside (above ambient outside), ID is the inside diameter of the round item, tw is the wall thickness of the wall item, and s is the allowable tension stress for the material used to make the (truly) round item. Solve that equation for whichever variable you want, and plug in numbers to evaluate.

This equation applies only to items loaded only in hoop stress by internal pressure, that are also very long (like a pipe), so that end blowout loads are "trivial". That's long cylinders. The tension stress in the membrane of a spherical item is twice as high; that's why cylindrical pressure vessels have thicker end heads than cylindrical sections.

None of this has anything at all to do with F=ma dynamics. It's nothing but statics. Period.

The "P ID" side of the equation is really P ID L, the blow-apart force where P is the pressure acting upon the area ID L. The "2 tw s" side of the equation is only the stress s acting upon the material area 2 tw L, comprising both sides of the pipe (both is why the "2" is there). Force equals force. The L on each side divides-out. Simple as that.

Statics. No accelerations of anything at all.

What you want to use for allowable stress "s" depends upon the situation. If for a one-time-only event, and one where deformation is NOT an issue, you can use material ultimate factored down by some appropriate safety factor. If deformation IS an issue (such as for seals actually sealing), you use a factored-down yield stress for a one-time event. If multiple events are possible, you use what is called a "fatigue S-N curve" to set an appropriate stress far below yield, so that the part can function N times. This requires a safety factor on the order of 10 minimum.

The S-N curves typically flatten out to zero slope below a certain rather low stress level. If you stay below that low stress level, you have an infinite fatigue life. That was the "secret" that has allowed the DC-3 to fly some 85 years since the very last one was ever manufactured, without one single structural failure in flight (not caused by weather or enemy action).

GW

Last edited by GW Johnson (2018-03-10 18:15:45)

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