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#1 2018-03-05 17:30:06

louis
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From: UK
Registered: 2008-03-24
Posts: 5,068

Construction technology for Mars?

Robotic construction technique for Mars?  What do you think?

https://www.youtube.com/watch?v=v4IbS42D8jk

Labour will be in very short supply on Mars so I think robotic construction makes sense.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#2 2018-03-05 18:54:56

SpaceNut
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Registered: 2004-07-22
Posts: 16,473

Re: Construction technology for Mars?

Not again 3D Printed Houses on Mars? .....

Not sure that we will print a large city but the tall buildings could be the anchors for a dome....

I do see, 3D concrete printer with contour crafting on the page....

But yes robotics will be of great importance as men are in short supply but it will be the mass and when we deliver it to mars that is the issue......not really the technology

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#3 2018-03-05 19:05:11

louis
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From: UK
Registered: 2008-03-24
Posts: 5,068

Re: Construction technology for Mars?

I've referenced this technology before but I think this is the first time I've seen this video applying it directly to Mars.

SpaceNut wrote:

Not again 3D Printed Houses on Mars? .....

Not sure that we will print a large city but the tall buildings could be the anchors for a dome....

I do see, 3D concrete printer with contour crafting on the page....

But yes robotics will be of great importance as men are in short supply but it will be the mass and when we deliver it to mars that is the issue......not really the technology


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#4 2018-03-05 20:43:35

IanM
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From: Chicago
Registered: 2015-12-14
Posts: 276

Re: Construction technology for Mars?

Not sure if this is the right thread, but construction materials are also important. The regolith provides a practically unlimited supply of bricks for external walls. Apparently there are also calcium-rich veins on Mars https://www.nasa.gov/mission_pages/msl/ … 16615.html, which can be mined to make various sorts of plasters, limes, and drywalls.


The Earth is the cradle of the mind, but one cannot live in a cradle forever. -Paraphrased from Tsiolkovsky

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#5 2018-03-06 05:15:11

elderflower
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Registered: 2016-06-19
Posts: 1,138

Re: Construction technology for Mars?

All proposed materials using regolith, except for glass, will require the availability of water. Bricks, cement, plaster etc.

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#6 2018-03-06 15:00:59

RobertDyck
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From: Winnipeg, Canada
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Re: Construction technology for Mars?

Robots that lay brick. Both of these require a human to feed bricks into the machine, and finish the wall. However, the first one is operational right now and lays 3 times as many bricks as a person. The second is more compact, small enough to roll through a doorway, but only a laboratory prototype.

SAM: Semi-Automatic Mason
hqdefault.jpg?sqp=-oaymwEXCNACELwBSFryq4qpAwkIARUAAIhCGAE=&rs=AOn4CLBbFvvKrgLAthPRsS9FQluNFpR7Eg

AMPRO BR
hqdefault.jpg?sqp=-oaymwEXCNACELwBSFryq4qpAwkIARUAAIhCGAE=&rs=AOn4CLA0TIZxlnecsctb_EFkZyioI0uytw

I'm thinking of Bruce Mackenzie's idea of Roman aches on Mars. A habitat built with brick, with regolith piled on top for both counter-pressure against internal air pressure, and radiation shielding.

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#7 2018-03-06 15:13:58

louis
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From: UK
Registered: 2008-03-24
Posts: 5,068

Re: Construction technology for Mars?

We are told that bricks can be constructed from compressed Mars regolith.  It's not that difficult to imagine a pretty seamless construction line of brick poduction, brick delivery and the walls being built robotically.

RobertDyck wrote:

Robots that lay brick. Both of these require a human to feed bricks into the machine, and finish the wall. However, the first one is operational right now and lays 3 times as many bricks as a person. The second is more compact, small enough to roll through a doorway, but only a laboratory prototype.

SAM: Semi-Automatic Mason
https://i.ytimg.com/vi/MVWayhNpHr0/hqdefault.jpg?sqp=-oaymwEXCNACELwBSFryq4qpAwkIARUAAIhCGAE=&rs=AOn4CLBbFvvKrgLAthPRsS9FQluNFpR7Eg

AMPRO BR
https://i.ytimg.com/vi/_rQIH0Bnb8g/hqdefault.jpg?sqp=-oaymwEXCNACELwBSFryq4qpAwkIARUAAIhCGAE=&rs=AOn4CLA0TIZxlnecsctb_EFkZyioI0uytw

I'm thinking of Bruce Mackenzie's idea of Roman aches on Mars. A habitat built with brick, with regolith piled on top for both counter-pressure against internal air pressure, and radiation shielding.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#8 2018-03-06 15:17:01

RobertDyck
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Re: Construction technology for Mars?

A larger machine, this time a vehicle, but still doesn't require a bridge crane like a 3D printer. This one is built by Fastbrick Robotics, they partnered with Caterpillar to increase sales.

Hadrian
hqdefault.jpg?sqp=-oaymwEXCNACELwBSFryq4qpAwkIARUAAIhCGAE=&rs=AOn4CLCAhFhphWLuAH24i5HtYVkTQxfhvg

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#9 2018-03-07 12:32:45

GW Johnson
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From: McGregor, Texas USA
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Re: Construction technology for Mars?

Point 1:  how are you going to pressurize a brick wall,  without blowing it to pieces?  Brick masonry is good ONLY in compression.  Pressurizing inherently loads a wall in bending and tension. 

Same is true of concrete,  in reality.  It can be used in bending and tension to some extent,  but only with great care designing the steel reinforcing,  which carries essentially 100% of those loads.  If you have to carry such loads with the steel anyway (and you do with ANY pressurized building),  then of what use is all that concrete?

Point 2:  for arch construction dead-loaded above to counter pressurization forces within,  so that the structure really can be compression-loaded masonry,  what do you do to hold up the arch during construction with all its deadload on top?  Before you actually pressurize it?  I already know the answer:  it must be strong enough to more-than-hold-up all the deadload completely unpressurized. 

That means that you WILL NOT get by with a minimum material design!  Period!  End of issue!  Nothing else qualifies as practical construction techniques.  Not here,  and not there.  Most major construction accidents are collapses of temporarily-inadequately-braced structures not yet completed.  The easiest and safest way to build your arch is atop sand fill.  You dig it out after completion. It's A LOT of effort and earth-moving to do it that way,  but by far the safest. 

And it certainly means trying to size things with published material strengths is naive in the extreme.  Your working stresses are more than a factor of 10 reduced from just the yield strengths,  much less the ultimates. 

Further,  this kind of work cannot be done by a man is a stiff,  bulky,  constraining gas balloon space suit.  Not even as a heavy equipment operator.  Construction work in vacuum is THE argument for MCP suits done as vacuum-protective underwear beneath conventional insulating garments.  If you have ever done this kind of work,  then you already know the truth of what I say.

Sorry to be busting bubbles,  if y'all will forgive me that particular choice of words! 

(That was a joke!)  --  GW

Last edited by GW Johnson (2018-03-07 12:44:43)


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#10 2018-03-07 14:39:16

RobertDyck
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From: Winnipeg, Canada
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Re: Construction technology for Mars?

GW Johnson wrote:

Point 1:  how are you going to pressurize a brick wall,  without blowing it to pieces?...

Point 2:  for arch construction dead-loaded above to counter pressurization forces within,  so that the structure really can be compression-loaded masonry,  what do you do to hold up the arch during construction with all its deadload on top?  Before you actually pressurize it? ...

Here are images from the Mars Homestead Project, phase 1, Hillside Settlement. Cross-section shows you how it works. Settlement is built by "cut and cover": dig out a side of a hill, build brick in the cut, then push regolith down to bury it. That's the reason for a hillside; you always move dirt down, never up. This can be done by an electric track Bobcat sized for Mars.

The main atrium is buried deep within the hillside. There is regolith both above and to the sides to provide counterpressure against internal air pressure. Sections close to the hill edge have brick or reinforced concrete to support regolith for radiation shielding, but are not pressurized. Within that are modules made of material that doesn't require counterpressure: stainless steel, aluminum alloy, or fibreglass. This image shows a vehicle airlock/garage. Actually, I argued to bury the edge module directly, not use brick/concrete for regolith. But the architect Georgi chose to do it this way so the pressure hull could be accessed to be patched/repaired.

Also note the sunlight tracker/reflector on the hilltop, with a light pipe leading to a diffuser at the apex of the groin arch. This allows the deeply buried brick atrium to receive natural sunlight. With trees in pots for aesthetic appeal.
normal_MHP-4FC-Image014.jpg

Overview of the 12-person base once complete.
normal_MHP-4FC-Image001.jpg

An artists view of the inside of the atrium.
normal_MHP-4FC-Image029.jpg

GW Johnson wrote:

Further,  this kind of work cannot be done by a man is a stiff,  bulky,  constraining gas balloon space suit.  Not even as a heavy equipment operator.  Construction work in vacuum is THE argument for MCP suits done as vacuum-protective underwear beneath conventional insulating garments.  If you have ever done this kind of work,  then you already know the truth of what I say.

Damn right! This is the first prototype MCP spacesuit, built by Paul Webb in 1967, paper submitted for publication December 1967, published in the April 1968 edition of the Journal of Aerospace Medicine. These images are taken from your website. wink
leotard.jpg backbend%2Btest.png ladder%2Btest.png vac%2Btank%2Btest.png

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#11 2018-03-07 14:46:15

RobertDyck
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From: Winnipeg, Canada
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Re: Construction technology for Mars?

I've posted these before, but... A track Bobcat. Generic term is compact track loader.
bobcat-t595-trailering-t6k1552-16j1-fc-promo_ci_horizontal_small.jpg

And YouTube video of a Bobcat converted to full electric. 72-volt AC motor, lithium-ion batteries.
hqdefault.jpg?sqp=-oaymwEXCPYBEIoBSFryq4qpAwkIARUAAIhCGAE=&rs=AOn4CLDyZxtbhId4jhC29htLMkCbvJLRLg

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#12 2018-03-07 14:55:57

JoshNH4H
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From: Pullman, WA
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Re: Construction technology for Mars?

Construction technology obviously depends on what you're trying to build.  So I'm going to start with a quick description of how I think Martian buildings ought to be designed and then move on to how you might go about building them.

The key difference between a Martian building and a Terran building is that Martian buildings will double as pressure vessels, probably containing roughly 50 kPa (half an atmosphere) of pressure.  It's surprisingly hard to find data on the weights of buildings, bu I did find this, which gives standard approximations for the "live loads" in a building (i.e. the movable loads that are not part of the structure).  It says that you should expect a live load of 50 lb per square foot per floor in an office (2.4 kPa/floor).  This means that in a certain way a one-story Martian building is comparable to a 21 story office building.

Pressure containment considerations therefore dwarf pretty much everything else, and buildings are much bigger than a normal kind of pressure vessel.  What I want to do, which will make construction much easier, is to contain pressure in the vertical direction with a pile of regolith or sand bags on top of the building.  50 kPa of pressure corresponds roughly to 5 m of rammed Earth or 7 m of sandbags.

That takes care of the vertical direction, but the horizontal direction matters too, and this is where the design is clearly superior to others.  The building can be a square or rectangle shape, which is important because circular rooms necessarily create wasted space.  Pressure will be contained with steel cables (similar to those on a suspension bridge) in the floors and ceilings.  The outer walls will be made from steel, curved outwards to contain the pressure.

The construction process will be as follows:

  1. Dig a hole for the foundation

  2. Fill the hole with concrete, rammed earth, etc. as a foundation

  3. Build a compressive support structure from that foundation able to support the entire load of the counterweight

  4. Build a platform on top for the counterweight.  The platform needs to be mounted on the compressive structure in a flexible way so that it can go up and down by maybe as much as 10-20 cm (this guarantees that the full atmospheric pressure will be transferred up into the counterweight rather than down into the compressive structure, which may not be able to handle it)
    4a. If desired, build the counterweight in such a way as it can serve double-duty, pushing down on the building below while it also pulls down on a greenhouse above.

  5. Assemble the counterweight on top of the platform

  6. Assemble the horizontal pressure containment layers from pieces of curved steel bolted together, hooked into steel cables, and resting on the compressive structure.

  7. Pressurize

  8. Build out the different levels with internal furnishing, floors, walls, etc. as desired

Out of all these activities, I think the following ones could be automated:

  • Digging the hole for the foundation

  • Filling the hole with concrete (or a different foundation material, depending on what's most economical)

  • Building the compressive support structure: This might take the form of a few brick or concrete columns.  I'm imagining in my head a machine that comes packed with a load of brickmaking materials and builds a tower underneath itself to a specified height or according to specified designs.  It might use solar power to cook the bricks and then lay them accordingly.

  • The platform's frame will probably be made from welded steel.  While it's certainly possible for robots to weld I don't know if it would make sense or not to have them do so.

  • Building the counterweight (whether it be made from bricks or sandbags or rammed earth) is a process that could be automated

  • The horizontal pressure containment layers could probably be automated but because there won't be that many in each building it probably does not make sense to do so.

  • Pressurization will certainly be automated

  • Internal fittings will almost certainly require some human labor

Greenhouses obviously are a totally different beast.  What do you all think?


-Josh

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#13 2018-03-07 21:17:36

IanM
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From: Chicago
Registered: 2015-12-14
Posts: 276

Re: Construction technology for Mars?

I would assume that a Martian building would likely contain around 1 atm of pressure (101,325 Pa, by definition) in order to best simulate Terran conditions. In imperial units this translates to ~14.7 psi, rounded up to 15 for safety.

According to https://www.gpo.gov/fdsys/pkg/GOVPUB-C1 … b23c4d.pdf, a brick wall with high-bond mortar and no vertical load can at best withstand 2 psi, and really more like 1.5 (and even vertical loads up to 150,000 lb don't let it reach 7). So a tenth of what would be needed. The force in question is the pressure gradient force, which depends on the change of pressure over the change in distance. If we really really wanted to make brick walls above ground on Mars, we would increase the distance between the 1 atm interior and the very low pressure environment, which in practice would mean increasing the thickness of the wall.

Assuming for both safety and simplicity that the Martian atmosphere is a vacuum at 0 atm/Pa/bar/psi/etc., and that the density of the air is the same as on Earth (1.2 kg/m^3), the magnitude of the acceleration due to the force using SI units is (101,325/1.2*thickness). Since I'm ultimately trying to get a pressure from an acceleration, I make up a couple of figures, but I hope they are somewhat reasonable. We need a mass of air to get a force; assuming a Martian brick building is around 100 m^3 in volume, this would give 120 kg of air, so the total force in N is thus (10,132,500/thickness). I assume that the height of the building is 5 m, leaving 20 m^2 for floor area. For a cylindrical building this gives an ~80 m^2 wall area (I'm neglecting the roof); doing the same for a square yields 25 m^2 for wall area. Pressure is Force/Area, so for the cylindrical building this gives (126,656.25/thickness) and (405,300/thickness) for the pressure. Maximum value was around 1.5 psi, but I'm going for a factor of safety of 2 so will thus cut the maximum pressure to 0.75 psi, which is ~5,175 Pa. This yields a minimum thickness of 24.5m for a circular building and 78.5m for a square building.

GW said that using published maximum strengths is a bit naive, which wouldn't surprise me. But even with such naivete it becomes apparent that a brick wall above the ground would not be feasible.


The Earth is the cradle of the mind, but one cannot live in a cradle forever. -Paraphrased from Tsiolkovsky

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#14 2018-03-08 09:11:22

JoshNH4H
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From: Pullman, WA
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Re: Construction technology for Mars?

Hey Ian,

I agree with your conclusion in that post but I am very confused about your methods. 

If I had a circular pressure vessel with 20 square meters of floor area and wanted to calculate the minimum required wall thickness, I would do it as follows:

Looking at your reference, I see the tensile strength of brick walls cited as 50 psi-300 psi (pg. 45), not 2 psi.  This is equal to 350-2100 kPa.  I seem to recall that individual bricks have tensile strengths around 10 MPa (please don't cite me on this), so it makes sense that the wall would be less than that.

It's the process of calculating the required thickness where I think I really don't understand what was happening in your post.  Here's how I would calculate the theoretical required wall thickness:

2f069hz.jpg

This is basically a free-body diagram of one-half of the habitat, showing that pressure containment is a balance between the pressure force from the air and the tensile restraint of the structure. In this diagram:

Fp=Force of Pressure
Ft=Force of tension
tw=Thickness of the wall
h=Height of structure
r=Inner radius of structure
Pi=Internal Pressure
Po=External Pressure
σt=Effective tensile strength of the structure, including safety factor

Plugging in to the equation in black:

2*(Pi-Po)*r*h=2*σt*tw*h

Cancelling and solving for tw:

tw=(Pi-Po)*r/σt

Plugging in values (a=20 m^2 implies r=2.5 m; Pi-Po=100 kPa, per your post even though I believe a lower figure is more reasonable, and σt=30 psi/200 kPa) I find that the wall thickness would need to be 1.25m.

This is a lot, and also is not the only reason you wouldn't want to use bricks.  Other reasons include:

  • Bricks are not airtight and will leak a lot

  • The mortar holding brick walls together weakens over time which creates a risk of explosive decompression

  • The combination of the above two points with a large thermal gradient and the extreme cold outside the wall leads to conditions where this damage could happen much faster.  Imagine this: somewhat-humid air (such as you might find in any comfortable environment) seeps through the brick.  Water condenses out of the air and then freezes and expands.  This causes cracks, which will grow over time due to faster air flow and thermal cycling.

  • What about vertical tensile stress?

  • A fault in any individual brick or improper bricklaying in any section of the wall is a risk to the integrity of the entire structure

  • Why in god's name would you choose to use a material that has garbage tensile properties in a tensile application when there are materials that do *not* have garbage tensile properties? Steel is well over 100 times stronger in tension than brick.

As far as square buildings containing pressure with their outside walls--I don't believe this is possible.  You would expect them to literally burst at the seams.

It's possible that I simply did not understand your method but we do have very different results.


-Josh

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#15 2018-03-08 09:59:26

Terraformer
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From: Lancashire
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Re: Construction technology for Mars?

I've suggest hexagonal structures before, for Luna. An outer wall, a circular pressure vessel within that, and then an inner wall within the pressure vessel. That way they can be tessellated together, whilst avoiding some of the problems of planning a circular space. Have apartments surrounding a central park, with light diffusers.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#16 2018-03-08 10:47:44

RobertDyck
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Re: Construction technology for Mars?

(sigh!) I posted pictures. The idea of brick isn't my idea, it's Bruce Mackenzie's. In fact, I was embarrassed that I picked holes in his idea. But we found solutions for the problems. First basics:

  1. dig a cut in the side of a hill. Ensure ground at the cut is level with the ground in front of the hill

  2. construct a brick building with Roman arches: barrel arch, or groin arches. Construction done unpressurized

  3. bury the building. Ensure regolith is so deep that there is more pressure on the roof than air pressure you will later fill it with

  4. pressurize the building

Pressure: NO! Do not pressurize to 1 Earth atmosphere. Robert Zubrin argued to use the same pressure as Apollo and Skylab. That was 5.0 psi total pressure with 60% O2, 40% N2. That is 3.0 psi partial pressure O2, and 2.0 psi partial pressure N2. It worked for Apollo, it worked for Skylab, and it allowed decompressing to spacesuit pressure with zero prebreathe time.

Shuttle and ISS operated at 1 atmosphere. That's stupid. Shuttle required 17 hours of oxygen prebreathe time before an astronaut could decompress into an EMU suit. Apollo originally intended suits to use 3.3 psi pure oxygen, the cabin would use 3.0 psi pure oxygen. That allows 10% pressure loss in the suit without any difficulty breathing. The Apollo 1 fire happened when they pressurized the cabin to 17.7 psi pure oxygen. That was 3.0 psi plus Earth ambient pressure, so stress on the hull would be the same as space. But 17.7 psi pure oxygen is not at all the same as 3.0 psi; it's an extreme fire hazard. The manufacturer of the Apollo capsule said DO NOT DO THAT! But NASA management didn't listen. Earth's atmosphere is 14.695950 psi at sea level. But if you measure it that precisely, barometric pressure will fluctuate with weather. Earth has 20.946% O2, so partial pressure at sea level is 3.078 psi. Apollo and Skylab used the same partial pressure O2 as the launch site at KSC.

I have argued to reduce pressure on Mars. After all, Boulder Colorado has 2.54 psi partial pressure O2. To start with, reduce Mars spacesuit pressure to 3.0 psi partial pressure O2. That using the old Apollo rule of the habitat having 10% lower partial pressure O2 than the spacesuit to allow for a leak, that would give a Mars habitat 2.7 psi partial pressure O2. Notice that is already more than Boulder. Add nitrogen gas to the maximum without requiring oxygen prebreathe for decompression to spacesuit pressure. The rule is partial pressure N2 in the higher pressure environment cannot be more than 1.2 times total pressure for the lower pressure environment. That means 3.6 psi partial pressure N2. Harvest N2 from Mars atmosphere. I have posted several times how; the easy way is to use a freezer to remove bulk CO2, and a rhodium catalyst to react carbon monoxide (CO) with oxygen to form CO2. Do that in the same canister where you freeze CO2, so that is removed too. There isn't much O2 in Mars atmosphere, but there is more than CO, so this will work. Furthermore, the same catalyst will decompose ozone into more O2. The result is primarily N2 and Ar. In the habitat, keep the ratio of N2:Ar the same as Mars ambient, that way you don't have to bother separating them. Earth has 0.9340% Ar, so you're breathing Ar right now. Viking 2 lander measured Mars atmosphere to have 95.32% CO2, 2.7% N2, 1.6% Ar, 0.13% O2, 0.07% CO, 0.03% water, and trace gasses. Curiosity rover has measured it a little different. According to published results from Curiosity, Mars atmosphere has 95.97% CO2, 1.93% Ar, 1.89% N2, 0.146% O2, 0.0557% CO. We know that on Mars CO2 fluctuates with weather, but the ratio of N2:Ar is significantly different. Measurements were made 4 decades apart, and different locations on Mars. Using data from Viking, that would give cabin air 2.133 psi partial pressure Ar. Using Curiosity data, it would be 3.676 psi partial pressure Ar. There is also a maximum partial pressure Ar for zero prebreathe time, this figure would exceed it. This would also increase total pressure in the habitat. We could set partial pressure Ar to 1.2 times total pressure in the suit, so 3.6 psi. That would make N2 3.525 psi partial pressure. Using Viking data, total pressure in the habitat would be 2.7 + 3.6 + 2.133 = 8.433 psi = 0.57383 atmospheres. Using Curiosity data, total habitat pressure would be 2.7 + 3.6 + 3.525 = 9.825 psi = 0.66855 atmospheres. That significantly increases pressure. We could reduce diluent gas, dropping to 8.0 psi total pressure.

The point is WHY IN GOD'S NAME WOULD YOU CHOOSE 1 EARTH ATMOSPHERE PRESSURE!?!? DON'T DO THAT!

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#17 2018-03-08 11:10:49

RobertDyck
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From: Winnipeg, Canada
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Re: Construction technology for Mars?

I should mention my criticisms of Bruce's idea. First, a tunnel through the dirt to an exterior door will not have full counterpressure from regolith. The closer you get to the edge of the dirt, the less counterpressure. The door frame will have zero counterpressure. So a tunnel through the dirt to an exterior door must be made of something else. I recommended stainless steel, or aluminum alloy, or fibreglass.

The second issue is air pressure finds a way out. It will find the weakest point, and leak out there. Air pressure will push a channel through loose regolith (dirt) to the surface, allowing the habitat to leak. Solution: spray a sealant on the brick. The sealant should be sprayed on the inside surface so air pressure pushes into the brick. As opposed to outside where pressure would lift it off the brick.

Advantage to Bruce's idea is that bricks can be made very simply. From typical Mars surface material (dirt).

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#18 2018-03-08 11:34:30

JoshNH4H
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From: Pullman, WA
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Re: Construction technology for Mars?

Hey RobertDyck,

I did see your picture but was not responding to your design.  The Mars Homestead design definitely has some benefits but it also is far from perfect especially if you're looking to build a whole city, rather than a small base.

In any case, simply burying the habitat does not free you from the necessity of containing pressure in the horizontal direction.  Brick is still a bad structural material, even for a buried habitat.

I agree with you on atmosphere (even if I generally spec for a somewhat higher pressure than you've suggested).  IanM, if you're interested, Midoshi posted a really excellent and well-researched thread about minimal Martian atmospheres a while back.


-Josh

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#19 2018-03-08 11:50:58

JoshNH4H
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From: Pullman, WA
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Re: Construction technology for Mars?

Terraformer-

What size would you have the hexagons be? How would you construct the pressure vessel?


-Josh

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#20 2018-03-08 12:35:47

Oldfart1939
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Registered: 2016-11-26
Posts: 1,756

Re: Construction technology for Mars?

What is the current pressure in ISS? Atmospheric composition? That's a suitable starting point for the habs on Mars. I wouldn't discount brick entirely, but my formulation and sizing would be radically different than Earth bricks. And my construction techniques would differ as well. Instead of a single wall construction, I would utilize a double wall with regolith packed in the space between walls. This serves to add weight and strength to the structure as well as being thermal insulation in addition to radiation attenuation. There is a Canadian Cedar home company called Pan Abode which utilizes a double wall construction technology for homes built in the frozen North.

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#21 2018-03-08 12:51:26

IanM
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From: Chicago
Registered: 2015-12-14
Posts: 276

Re: Construction technology for Mars?

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.


The Earth is the cradle of the mind, but one cannot live in a cradle forever. -Paraphrased from Tsiolkovsky

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#22 2018-03-08 13:01:02

RobertDyck
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Re: Construction technology for Mars?

JoshNH4H wrote:

The Mars Homestead design definitely has some benefits but it also is far from perfect especially if you're looking to build a whole city, rather than a small base.

Ok. Intention was to build an initial settlement. I suggested we restrict scope to the task at hand, the goal was to design the habitat for the first ever permanent human settlers. So rather than design a new spacecraft to carry settlers/workers/astronauts to Mars, we assumed Mars Direct habitats. Notice the image shows 4 of them. Each would carry 4 crew, the 4th would be for redundancy. There's a lot of redundancy in Mars Direct, but this would be for crew who will live there the rest of their lives. So for redundancy, before the large base is ready, a spare habitat is delivered. This has living space, life support, and more tools. Each Mars Direct habitat would include a rover, but the one delivered without crew would carry an earth-moving construction vehicle, a compact track loader. I keep using the brand name "Bobcat" because that's the one I'm familiar with. Brandt also builds them, a division of John Deere. Caterpillar Equipment known as "Cat" does too. Takeuchi is a Japanese company that makes them, has a distribution and sales facility in Atlanta. There are probably others.

But the point was Mars Homestead would arrive on Mars with nothing before it. Mars Direct habitats would deliver crew with tools. Additional cargo landers would deliver more tools and equipment. They would build a permanent home for themselves, then expand it for an additional 12 crew. Once this base has 24 crew with mining/refining and fully equipment manufacturing, they would build a separate facility for the first 100. We took the phrase "first 100" from the book "Red Mars". This is long before Elon Musk presented his BFR. The base for the first 100 would be designed so their first task will be expanding it for the next 100, with expansion for 1,000 and more. The first city. We didn't expect the city would be built of brick. At least I didn't.

JoshNH4H wrote:

In any case, simply burying the habitat does not free you from the necessity of containing pressure in the horizontal direction.

Now we're talking about lateral earth pressure. Yes, Mars regolith isn't "earth". However, there is a lot of research into lateral earth pressures for a retaining wall for construction here on Earth. Mars surface material is not pulverized igneous minerals like the Moon, it has clay and gypsum and other hydrated and hydrologically weathered material, and sedimentary material. If you want to be nit-picky, the loose surface material on Mars isn't regolith. It isn't soil either, because there's no organic material. The most accurate term in the English language would be "dirt". It's dirt. And since there is clay, research into lateral earth pressure here on this planet does directly relate. Here's one document about that.
Lateral Earth Pressures and Retaining Walls

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#23 2018-03-08 13:38:26

RobertDyck
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Re: Construction technology for Mars?

Oldfart1939 wrote:

What is the current pressure in ISS? Atmospheric composition?

They use 1 atmosphere, same as Earth at sea level. And same composition. High altitude locations on Earth have lower pressure, such as Boulder Colorado. I keep using that as comparison because Mars Society conventions were held there many years.

I wouldn't start with that. When Robert Zubrin and his partner David Baker devised Mars Direct, they assumed the same pressure and composition as Apollo and Skylab. That sounds like a good starting point. (And NASA would most likely accept that.)

Also realize the crew size of Mars Direct was 4 because NASA had assumed a Mars mission would have 4 crew. They assumed that from 1965 until some time after Mars Direct. The reason was work on a Mars mission in the 1960s tried to use as much Apollo hardware as possible. An Apollo capsule could carry 3 astronauts to the Moon, plus food and lithium hydroxide canisters for life support. If the storage space behind the seats was not used for food and supplies, it could be used for something else. When Skylab was in space, they built a rescue Apollo spacecraft just in case. It had 2 more seats in that space behind the 3 "main" seats. When they devised a plan for Mars, they found the Avcoat heat shield was not good enough. They came up with the first PICA heat shield in 1970s. Dragon today uses PICA, but NASA announced it in 1970 as an upgrade for Apollo to Mars. The 1970 version was 3 times as heavy (massive) as an Avcoat heat shield, but able to protect an Apollo capsule entering Earth's atmosphere the same way as it did when returning from the Moon, but at the speed it would have when returning from Mars. This additional weight meant an Apollo capsule could only carry 4 astronauts, not 5. Food and life support supplies would have to be stored in a separate deep space habitat. But that's where the crew number of "4" came from: the number than an Apollo Command Module could carry. Robert Zubrin later gave a justification of 2 exploration teams: each with 1 scientist and 1 engineer to fix stuff. But that was an excuse; he really started with the crew size that NASA assumed. And NASA got that from Apollo.

Oldfart1939 wrote:

Instead of a single wall construction, I would utilize a double wall with regolith packed in the space between walls. This serves to add weight and strength to the structure as well as being thermal insulation in addition to radiation attenuation. There is a Canadian Cedar home company called Pan Abode which utilizes a double wall construction technology for homes built in the frozen North.

All homes in Canada are insulated. It's cold in winter. Typical construction until 1920s was 2x4 timber, with exterior siding attached directly and plaster/lathe walls inside. At that time a 2x4 was 2"x4". The 4" space was filled with insulation. In the 1920s, lumber companies got cheap. Their excuse was finishing rough lumber to produce a smooth surface required planing, so the sold 2x4 timber as 1¾"x3¾". Then in the early 1960s they got cheap again, 2x4 timber was actually 1½"x3½". Insulation material got better, but the cavity got smaller. Instead of 4" deep wall cavity, it was only 3½". In the 1970s they changed again; instead of 2x4 timber on 18" centre spacing, they used 2x6 timber on 24" spacing. The volume of timber in the wall is actually the same, so the wall is just as strong, but the wall cavity is larger allowing more insulation. However, realize 2x6 is actually 1½"x5½" so wall cavity is actually 5½" deep. And we haven't used plaster/lathe for a long time. Homes are built with drywall. Typically today homes are built with OSB exterior sheathing nailed or screwed to the 2x6 frame, and drywall nailed or screwed to the interior of that same frame. Vapour barrier applied to the exterior of the OSB sheathing, then siding applied to that.

If the company you named is not using modern materials, but adobe instead, they will still have to produce some sort of cavity for insulation. It's cold up here.

For Mars, I was thinking of galvanized steel sheet metal wall studs like modern office walls, and drywall applied to that. Drywall usually is made of gypsum with paper facing. Manufacturing technique: lay heavy paper down first, pour a thick slurry of gypsum and water, lay the top paper on top, then bake the water out. Industrial operations on Earth do this as a continuous ribbon, cut the dry product into boards, then apply edge tape. Mars won't have trees, so using paper isn't practical. Georgia Pacific makes drywall with fibreglass felt facing instead. It's highly resistant to mildew, so appropriate for high humidity areas like a bathroom. And using 3/8" thick drywall intead of 1/4", and fibreglass fibres embedded within the gypsum, it can withstand a raging house fire for up to 60 minutes before collapsing. So I suggest using that drywall on Mars.

But yes, for an initial base that doesn't have a large industrial base yet, double wall brick would make sense. But wouldn't you want thermal insulation, not just regolith? Something like fibreglass batt?

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#24 2018-03-08 14:07:42

RobertDyck
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Re: Construction technology for Mars?

Actually, you could build a large settlement into a hillside. Here are some images of Petra. Many of these are tombs, but some are homes. Mars could build homes like this.
petra-tomb.jpg
Sometimes-Petra-is-called-%E2%80%98Rose-City%E2%80%99due-to-Rose-Red-colored-sandstone-hills..jpg
Petra-8-974x350.jpg

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#25 2018-03-08 14:51:58

JoshNH4H
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Re: Construction technology for Mars?

RobertDyck-

Other than my point about bricks and horizontal pressure (which I address in the second part of this post), I have no issue with the Mars Homestead design.  It's smart to take advantage of geology and topography where you can, and with a whole planet to pick from and robotic scanners already looking it's probably worth trying to find somewhere that's nearly perfect.

Once you have a larger population and are building a town you won't be able to pick your spot so precisely, and you'll end up with different designs.  The point is not that the Mars Homestead design is wrong or bad, as it mostly is not, but just that there are plenty of different possible/reasonable designs out there each of which is worthy of consideration and which may be well-suited for different scenarios. Especially if you're in a kind of boomtown, it seems to me that construction on a flat plane has lots of advantages.

RobertDyck wrote:

Now we're talking about lateral earth pressure. Yes, Mars regolith isn't "earth". However, there is a lot of research into lateral earth pressures for a retaining wall for construction here on Earth. Mars surface material is not pulverized igneous minerals like the Moon, it has clay and gypsum and other hydrated and hydrologically weathered material, and sedimentary material. If you want to be nit-picky, the loose surface material on Mars isn't regolith. It isn't soil either, because there's no organic material. The most accurate term in the English language would be "dirt". It's dirt. And since there is clay, research into lateral earth pressure here on this planet does directly relate. Here's one document about that.
Lateral Earth Pressures and Retaining Walls

I had a look at that, as well as a couple others.  One that I found particularly helpful was this one, from the University of Utah Civil Engineering Department.

It seems like the basic model to determine the lateral earth pressure at a certain depth is:

Ph(d)=Pv(d)*k0

Where:

Ph is the horizontal (lateral Earth) pressure
Pv is the vertical pressure
k0 is a factor used to convert between the two

k0 is a function of the Poisson's Ratio (ν) of that soil, as follows:

k0= ν/(1- ν)

The .pdf contains this helpful table on page 4:

1ekvtw.png

You'd expect the local dirt on Mars to be something like unsaturated clay, sandy clay, or sand depending where you are exactly.  This means a Poisson Ratio between 0.1 and 0.4, and a value for k0 between 0.11 and 0.67.  Obviously this is a gigantic range.  You'll be able to test it somewhat on local materials, but there will still probably be a significant range that will need to be filled in.

A couple other points:

  • The numbers you get from these equations are equilibrium numbers, and equilibrium can take a long time to reach.  How long is it worth waiting?  How do you plan for changes over time?

  • As the dirt subsides it is somewhat liable to move around, especially if there's a substantial pressure on it.  Since your wall is not stiff enough to withstand the full internal pressure on its own, what happens if creep or subsidence opens up a void of any size near the outer wall of the structure?

  • More generally, how exactly are you making sure that the pressure really is being conferred into the walls?  Your picture suggested dirt would simply be pushed onto the structure which is not a very precise way of making sure there's an intimate connection between the two, as you would need with lateral earth pressurization

  • How much vertical pressure are you willing to design your structure to take?  Depending on your exact soil material, vertical pressure will be between 1.5 and 9 times as much as the horizontal pressure (this is the inverse of k0), with the horizontal pressure being equal to (or in fact exceeding, so as to make sure there is a safety factor--I used 1.3 below) the internal pressure.  This means that with your suggested internal pressure of 35 kPa (5 psi), vertical pressure will need to be between 68 kPa (10 psi) and 410 kPa (60 psi).  I don't mean to suggest that you need to build your building to withstand 4 earth atmospheres' of compressive pressure but you likely will get stuck with at least 1-2 full atmospheres in the vertical direction, which is a substantial downside to this method

  • I am simply not confident in the reliability and suitability of loose dirt as a critical structural element in a situation where people will die in the event of failure

  • Even in low-stress applications, bricks are only rarely used as load-bearing elements in the modern era


-Josh

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