Pyramid Greenhouse

Dook · 2016-11-01 14:46:30

Pyramid Greenhouse

Some time after a buried habitat is established a Pyramid Greenhouse could be built on the Mars surface directly over the buried habitat. Once finished, fruit trees that are growing in the buried habitat along with other fruit trees grown from seed, could be moved up to the Pyramid Greenhouse to make more room for growing vegetables in the buried habitat.

The bottom of the greenhouse is square, 28' wide by 28' wide, and the greenhouse panels are assembled on top of a foudation wall of lego blocks that are assembled in a trench that has the sides filled in. Each lego block is made of 1/2" thick fiberglass that is molded into a rectangular block 1' long, 6" tall, and 6" wide. This lego block foundation wall is built 2' tall, the top of the foundation is even with the surface of Mars.

The sides of the pyramid are angled 45 degrees. The center point of the greenhouse is 14' high. The depressurization area is made of fiberglass and has two fiberglass pressure doors.

The greenhouse has a Mars carbon dioxide atmosphere that is pressurized to just 2 psi, just enough to keep water in liquid form without putting too much pressure on the greenhouse panels. The pressure comes from a small air pump that is built into the wall of the depressurization area. The pump is manually turned on and takes in outside Mars CO2 and pumps it into the greenhouse. There is a gauge mounted on the inside of the depressurization frame. The pump does not need to be run every single time someone enters or exits but the greenhouse should be pressurized most of the time so water given to the trees stays liquid and does not evaporate.

The high CO2 level would help the fruit trees grow. The greenhouse absorbs heat during the day and cools slowly over night to keep the fruit trees from freezing. Also, some radiant heat from the buried habitat below would help keep the roots of the fruit trees from freezing.

The greenhouse is made of triple pane triangular plastic panels. The panels are filled with nitrogen (could be argon) when they are manufactured so there is no moisture inside of them to fog up. Each panel is 4' tall by 4' wide but that measurement is with them at the angle of 45 degrees. If stood straight up they are taller. The panels are six inches thick and each male panel has a 1" notch on all three sides that fits into the female panels around it. The panels are built with 1" of internal space between each pane and they have a 3" lip on the inside of the panel for bolting them together. The bottom row of panels are a bit different, the bottom of these panels fits into the top of the lego wall foundation. There is also a 2' tall tip cap piece that would be installed when about half of the top row is in.

The panels fit together (male panels pointed up, female panels pointed down) to form the walls. Most of the panels are pre-assembled in groups of five panels, three male bottom panels with two inverted female panels in between.

The sides of the pyramid are angled a bit extreme at 45 degrees to keep the center height reasonable, it's 14 feet. I didn't want to have to ship a lot of scaffolding. Because the sides are angled at 45 degrees there isn't room for a semi-dwarf tree to be planted until 7' in from the wall. So, if the trees are spaced every 3' you will have 5 trees per row. That's 25 semi-dwarf trees in the middle of the greenhouse but you need a center walkway so we would have 20 trees and then you would have a 7' walkway all around that you could plant vegetables or dwarf trees. Each tree in the greenhouse would be set into a large buried plastic tub and filled in with Mars regolith.

Over time oxygen given off by the fruit trees would accumulate at the top of the greenhouse. Once the quantity of oxygen gets to a high enough level it could be pumped into an oxygen bottle with a long tube and a small solar powered pump.

A dehumidifier would need to be operated inside once in a while to recapture water, evaporated moisture may condense on the inside of the cool greenhouse panels.

Scaffolding: fiberglass platform 4'x4' and 1/2" thick. In the middle of one side it has built in cylindrical receptors for the four foot fiberglass ladder and receptors are the corners for the four foot long cylindrical extendable fiberglass legs. The platform can be raised by adding in more cylindrical fiberglass legs. Each leg adds 4' to the height so the platform can either be raised 4' high, 8', or 12' high. And then you would fit in 4' ladder sections to the ladder as well.

Fruit trees: 20 total
4 apple, 4 peach, 4 almond, 2 walnut, 2 cherry, 2 pear, 1 apricot, and 1 plum.

The depressurization area has two fiberglass doors. 4' wide by 4' long and 8' tall, the actual doors are 3'x 7' and the whole thing is pre-assembled.

All together the Pyramid Greenhouse is made of a total of 130 clear plastic panels, 110 lego foundation blocks, the tip cap, the depressurization area, nuts/bolts, sealant, and scaffolding.

One Mars Cart can carry 240 panels at one time so it should be able to carry the entire Pyramid Greenhouse, the foundation blocks, the depressurization area, nut/bolts, sealant, and scaffolding in one trip.

The entire Pyramid Greenhouse can fit in a container that is 17' wide x 12' long x 12' high. I don't know it's weight but since the panels are plastic it wouldn't be very much. One Mars Direct mission could launch it and there would be a lot of room left for other supplies.

RobS · 2016-11-01 15:26:02

You'll need to start by putting oxygen in your pyramid; otherwise the trees will suffocate (yes, they need oxygen, too). The oxygen won't accumulate at the top of the pyramid; it'll diffuse around and mix with the CO2.

Dook · 2016-11-01 15:44:20

Okay, a small amount of oxygen could be released into the atmosphere with a small portable oxygen bottle.

I thought oxygen was lighter than CO2?

JoshNH4H · 2016-11-01 15:55:26

Oxygen is lighter than CO2 but diffusive forces are much stronger than gravity in this case. Sugar is heavier than water, but it dissolves just fine.

If this weren't the case we would all suffocate as the 0.04% CO2 and 0.9% Argon in the atmosphere would all hang out right down at the surface with layers of Oxygen and Nitrogen above. Separation into components doesn't happen until you get up into the thermosphere and beyond.

louis · 2016-11-01 16:55:53

I think the idea of a small (automated) pyramid greenhouse was what got Musk hooked on Mars - he was appalled to find that no space agency was interested in trying one out on Mars, despite his offer of funding.

Tom Kalbfus · 2016-11-01 20:49:28

Legos?

This picture looks like what your describing, but seriously, Legos?

Dook · 2016-11-01 23:10:25

The foundation blocks are lego blocks but they're big, 1' long and 6" wide. They're easy to assemble with a plastic mallet, made of lightweight fiberglass, and strong as heck if they're placed overlapping.

The sides of the greenhouse are not lego pieces, though, they're clear plastic panels.

I could say "Plastic bag hab? Seriously?"

Tom Kalbfus · 2016-11-02 08:50:45

Has anyone ever built an actual house out of legos, you know they type one can live in?

Dook · 2016-11-02 09:26:53

I don't know. It sounds like you never had lego's as a kid. If you overlap the blocks to build a wall it makes it very strong. The blocks fit together tight, they will have to be tapped in with a mallet and once together and sealed they're not coming apart.

My Buried Habitat idea that I posted weeks ago uses lego style blocks for the walls and lego style backing plates for the floor panels.

kbd512 · 2016-11-02 10:47:30

Sending complete rigid lego bricks that can hold the weight of the regolith would make the bricks heavier and more difficult to deliver to Mars.

Any thoughts on hollow lego bricks that could be filled with regolith on Mars?

It would basically be a lightweight version of the HESCO barriers with smaller foldable or stackable "bricks" that robots or astronauts could unpack and fill with regolith using a small earth mover. That would do away with the requirement for a heavier ATV / rover to move a substantial amount of regolith. The rover could be as small as the Spirit and Opportunity rovers. A second robot could stack the bricks.

The smaller the bricks, the longer it takes to fill and stack them but the easier it is to package the bricks for delivery to Mars and subsequent stacking to form walls. If two to four robots can operate 24/7, the walls could be built rather quickly. The actual mass and volumes of equipment and materials required to do this can be delivered by a single Dragon capsule, so this is a near term testable method for construction of GCR/SPE/CME radiation protection.

Dook · 2016-11-02 11:24:26

No. Plastic lego's are incredibly strong.

Buy a small lego set. Use one of the large plastic square or rectangle pieces for the bottom, build walls all around the sides, remember to overlap the wall blocks, don't put any support in the center at all, then use a large plastic piece on top of it as a roof and stand on it. It will hold you up. And those are hollow lego blocks made of plastic, mine would be made of fiberglass that is 1/2" thick.

We could fill the lego blocks with Mars regolith? I wouldn't, no need, too much extra work, plus the regolith would just fall out when you tried to place the lego block. The regolith would have to be mixed with water in an already warm and pressurized area, then the wet regolith poured into an upside down lego, then allowed to dry. I wouldn't waste the water on it. Also, the gas that gets trapped in the lego blocks when the wall is assembled would act as insulation.

Last edited by Dook (2016-11-02 12:58:44)

Dook · 2016-11-02 11:31:23

For those of you who never had lego's, the wall blocks need to be twice as long as they are wide, so 1' long and 6" wide, the reason for this is so you can overlap the blocks at the corners. This makes the corners really strong.

If you don't overlap the blocks the walls have very little strength and they will buckle.

Dook · 2016-11-02 13:30:51

Another thing that could be done to increase the strength of the assembled lego wall even further would be to modify the typical lego style and put a notch in the sides. Typical lego's lock on the bottom and on top but there is no sideways locking, well, the sideways locking comes by overlapping the next row on top.

If we put a 1" female indentation on one side and a 1" male notch on the other side of the blocks and overlapped them it would make an even stronger wall.

Last edited by Dook (2016-11-02 13:32:02)

kbd512 · 2016-11-02 14:25:08

How big would the transport vehicle have to be to deliver a significant number of these rigid lego blocks?

The reason I suggested using regolith filled semi-rigid plastic bags is storage volume.

Compute the volume of blocks required to bury a single level tuna can similar to the two level tuna can proposed by Dr. Zubrin, 33feet in diameter and 6 feet high, and then let us know how big the vehicle that carries them to the surface has to be.

Dook · 2016-11-02 15:04:50

I think the whole Pyramid Greenhouse would take up about half the space on a Mars Direct launch and would fit on one Mars Cart for towing back to base. I don't know the weight of these blocks. A block is 1/4" thick fiberglass molded into a rectangle shape with six 1' tall knobs on top for locking in to the block above it and three hollow tubes inside for locking to the block below. I don't think weight would be a problem at all because the whole greenhouse is made of plastic and fiberglass.

The blocks for this Pyramid Greenhouse foundation are the same size blocks I used for the walls in the Long Term Buried Habitat. They are 1' long, 6" wide, and 6" tall. Once again, the length of each block has to be twice the width and height for overlapping to work. So, if you wanted more strength, you could make 2' long, 1' wide, and 1' tall blocks, or even larger ones to build with.

If you increase their size too much it creates a different problem, the blocks fit together very tight, they will need a mallet to get them apart on Mars and you have to ship them fitted together to save room. If they are too big you will really have to pound on them to get them separated and the sides might crack.

I don't understand why you would want to use these blocks to bury a Zubrin tuna can. Aren't sand bags better for covering the top? The bags are very lightweight and take up little space.

Why would you ship all these blocks to Mars and not use them to make a second habitat that can be used to grow some plants and as a second habitat?

Dook · 2016-11-02 15:46:34

Okay, a space 10' x 10' x 10' would fit 4,000 blocks.

They would be assembled and would have to be tapped with a mallet to separate them.

Last edited by Dook (2016-11-02 16:20:47)

kbd512 · 2016-11-02 16:25:55

Hmm... Does devoting 1,100ft^3 in a lander to store plastic bricks seem reasonable?

Semi-rigid (foldable) PE fabric "brick" (miniature HESCO regolith storage bins):

PE Fabric Thickness: .125"
Dimensions: 12" x 6" x 6"
Collapsed Dimensions of 12" x 12" x ".25" (36in^3)

36in^3 = 0.0208333ft^3

1,100ft^3 = 1,900,800in^3

1,900,800in^3 / 36in^3 = 52,800 folded PE fabric bricks

Do you still want to store that many hard plastic lego bricks just to build a wall that provides no overhead cover?

Dook · 2016-11-02 17:34:16

If we built the walls of our habitat with those things, how much pressure will those regolith filled fabric bags hold back? Not very much, even a few pounds of pressure would leak through them.

How do you fix the roof panels to the top of those fabric bags of regolith? The roof panels have to hold 8 feet of regolith on top of them.

Yes, I still want to store many hard plastic lego wall blocks just to build a buried habitats walls that will be strong enough to hold up the roof and hold in pressure.

And, I think the entire Pyramid Greenhouse and Buried Habitat components will fit in one Mars Direct launch.

louis · 2016-11-02 18:15:07

I think lego building has come up before. It is a serious proposition. I recall someone producing some sort of concrete blocks that fit together that way.

Dook wrote:

The foundation blocks are lego blocks but they're big, 1' long and 6" wide. They're easy to assemble with a plastic mallet, made of lightweight fiberglass, and strong as heck if they're placed overlapping.
The sides of the greenhouse are not lego pieces, though, they're clear plastic panels.
I could say "Plastic bag hab? Seriously?"

Dook · 2016-11-02 18:26:24

Maybe the lego building topic has come up before, I don't know.

They don't need to be concrete. Fiberglass lego blocks would very strong. They would be brittle because of the cold but if they were assembled during the daytime when it's warm I don't think they would crack.

kbd512 · 2016-11-02 19:37:32

Dook wrote:

If we built the walls of our habitat with those things, how much pressure will those regolith filled fabric bags hold back? Not very much, even a few pounds of pressure would leak through them.

How do you fix the roof panels to the top of those fabric bags of regolith? The roof panels have to hold 8 feet of regolith on top of them.
Yes, I still want to store many hard plastic lego wall blocks just to build a buried habitats walls that will be strong enough to hold up the roof and hold in pressure.
And, I think the entire Pyramid Greenhouse and Buried Habitat components will fit in one Mars Direct launch.

The regolith bags are to shield the habitat from GCR/SPE/CME radiation, not some sort of makeshift pressure vessel. A purpose built inflatable fabric habitat module made from spectra (lighter, stronger kevlar) would work just fine on Mars and it works just fine in orbit attached to ISS.

If the makeshift pressure vessel you intend to construct ruptures, anyone inside is unconscious in less than a minute. That nonsense in hollywood movies about putting a spacesuit on in a few seconds or depressurizing / re-pressurizing has about as much to do with reality as reality TV. You can take my word for it, ask an astronaut, watch an EVA on ISS on TV, or read NASA's documentation on EVA's.

The military typically uses structural support beams for transmitting the load from the roof to the walls on their field fortifications. I suspect we'd do it the same way on Mars. I've never seen sandbag walls collapse without first sustaining a substantial amount of damage. There are entire houses built from sandbags with no other structural support, but the bags forming the roof are not 8 feet in depth.

Edit:

Your idea of building a base with bricks is a very good idea because it's low-mass, low-tech, low-cost, and it works here on Earth. However, the specific materials you want to use and the way you want to construct a pressure vessel are highly likely to have fatal effects if a seal ruptures. No company that I know of has ever constructed a pressure vessel using lego bricks, plastic sheeting, and sealant. 1 atm is 2116lbs/ft^2. That's a substantial amount of force. No sealant and plastic bag is going to withstand that kind of force very long when subjected to mildly cryogenic temperatures and sharp objects. Unfortunately, not every idea will work best exactly the way you originally envisioned it.

Last edited by kbd512 (2016-11-02 20:01:16)

Dook · 2016-11-02 20:46:39

Your regolith bags are to shield the hab from radiation? Then why did you compare them to the lego wall habitat building blocks and ask why I would want to fill my launcher with them when I could just use the fabric regolith bags?

If my makeshift pressure vessel ruptures anyone inside is unconscious in less than a minute. What happens if YOUR makeshift habitat ruptures? What happens if anyone's makeshift pressure vessel ruptures?

What's more likely have a rupture, pressure vessel made of thin plastic or fabric or walls made of locking fiberglass blocks? Also, if there is a sudden pressure loss the crew will grab Spare Air canisters mounted on the walls and then they will put on their Mars Suits. I don't want nitrogen in the hab so they won't be getting the bends.

Inflatables work fine on the ISS? Yeah, it's working fine, that's why everyone is afraid to go inside of it. They open the door, take a reading, and close the door quick.

The military uses structural support beams? So do architects, when they are needed, they also use columns. The roof isn't coming down because each ceiling panel is locked in to the walls on two sides and locked into the central fiberglass column. The internal pressure of the habitat will about perfectly balance the mass of the regolith on top but even with no pressure the roof will hold. Each ceiling panel will be sealed before being set in place and lock in to the walls and the central column. Then the connector plates will be sealed and tapped in to the seam of the ceiling panels underside and top to help hold the panels together.

You've never seen sandbag walls collapse? Then they are the greatest building material ever. Hmm, I wonder why no one is using them for buildings then? And to think of all the steel and glass we wasted on skyscrapers when we could have just stacked sandbags.

My idea is likely to have fatal effects if a seal ruptures? Uhh, what seal would that be? Are you talking about the silicone? A typical lego block is open on the bottom so to seal it to another would require silicone around the bottom and sides so, there wouldn't be one edge that would get sealed, there would be four on the bottom and the two sides. And sealant can be placed on the inside wall seams also. Once it's finished they would slowly pressurize it and check a gauge to see if there is a leak. The outside walls would have regolith poured in against them so they can't suddenly burst outward. Having it somehow suddenly fail instantly, is just not going to happen.

Get some lego's, build a wall, overlap the blocks, take some silicone and seal the seams, let it dry, then try to blow through it.

What happens if your inflatable ruptures? Does it collapse onto the crew? How do you fix it?

No company you know of has ever constructed a pressure vessel built out of lego blocks? How many of them have built habitats on Mars before?

So an inflatable is better than structural blocks?

No sealant and plastic bag is going to withstand the force of one atmosphere for very long? You said it. Talk some sense into these people who want to use inflatables to live in forever on Mars.

Last edited by Dook (2016-11-02 21:24:57)

kbd512 · 2016-11-03 01:59:35

Dook wrote:

Your regolith bags are to shield the hab from radiation? Then why did you compare them to the lego wall habitat building blocks and ask why I would want to fill my launcher with them when I could just use the fabric regolith bags?

I didn't fully understand what you intended to do because I didn't fully understand what magic having 8 feet of regolith atop the habitat provided, apart from substantial radiation protection. The weight of the Martian regolith over the top of the habitat didn't correspond to anything that would provide enough counter-force to hold any breathable partial pressure atmosphere, so that was my best guess. My best guess didn't correspond with what you proposed. Mea culpa.

Dook wrote:

If my makeshift pressure vessel ruptures anyone inside is unconscious in less than a minute. What happens if YOUR makeshift habitat ruptures? What happens if anyone's makeshift pressure vessel ruptures?

A purpose-built habitat module is not "makeshift". It is purposefully built to withstand over-pressurization, so rupture is less likely to occur. Any ruptured pressure vessel will kill everyone inside it who is not fully suited at the moment of rupture. NASA accidentally learned how fast someone loses consciousness from an accident in a vacuum chamber with a suited technician who accidentally broke the seal on a hose connected to his suit. He was conscious for 12 seconds, IIRC.

Dook wrote:

What's more likely have a rupture, pressure vessel made of thin plastic or fabric or walls made of locking fiberglass blocks? Also, if there is a sudden pressure loss the crew will grab Spare Air canisters mounted on the walls and then they will put on their Mars Suits. I don't want nitrogen in the hab so they won't be getting the bends.

A square pressure vessel is more likely to rupture than a cylindrical pressure vessel, whatever the material used. The forces acting on the pressure vessel are not evenly applied in all directions. There'd likely be uneven deformation with 8 feet of regolith over the top unless the density of the regolith was uniform and uniformly spread over the top, i.e. not just a dirt pile sitting on top of the habitat. This doesn't work from a basic engineering perspective.

Dook wrote:

Inflatables work fine on the ISS? Yeah, it's working fine, that's why everyone is afraid to go inside of it. They open the door, take a reading, and close the door quick.

No one is afraid to go inside it, but it's a test article and that's part of the test protocol. The $100B station is more important than a $17.8M science experiment collecting atmospheric and radiation data. Prior to being permitted to attach their module to ISS, Bigelow Aerospace flew two technology demonstrators in space for quite some time. NASA is pretty serious about testing these days.

Dook wrote:

The military uses structural support beams? So do architects, when they are needed, they also use columns. The roof isn't coming down because each ceiling panel is locked in to the walls on two sides and locked into the central fiberglass column. The internal pressure of the habitat will about perfectly balance the mass of the regolith on top but even with no pressure the roof will hold. Each ceiling panel will be sealed before being set in place and lock in to the walls and the central column. Then the connector plates will be sealed and tapped in to the seam of the ceiling panels underside and top to help hold the panels together.

How would you obtain an even load distribution over the top of the structure by piling up regolith using a dozer? I haven't seen too many perfectly square and dirt mounds. A pyramid would come closest to enabling even load distribution.

Typical housing foundations are made from concrete, steel reinforced concrete, or set into bedrock because foundations can and do settle unevenly over time. Have you devised a way to ensure the load doesn't change as the structure settles?

Dook wrote:

You've never seen sandbag walls collapse? Then they are the greatest building material ever. Hmm, I wonder why no one is using them for buildings then? And to think of all the steel and glass we wasted on skyscrapers when we could have just stacked sandbags.

Dirt is not the greatest building material ever, but it's all over the place on Mars.

James May actually built a lego house. The framing was wood 2x4's and it was on a concrete slab, but it's still pretty cool.

Dook wrote:

My idea is likely to have fatal effects if a seal ruptures? Uhh, what seal would that be? Are you talking about the silicone? A typical lego block is open on the bottom so to seal it to another would require silicone around the bottom and sides so, there wouldn't be one edge that would get sealed, there would be four on the bottom and the two sides. And sealant can be placed on the inside wall seams also. Once it's finished they would slowly pressurize it and check a gauge to see if there is a leak. The outside walls would have regolith poured in against them so they can't suddenly burst outward. Having it somehow suddenly fail instantly, is just not going to happen.

You could glue a plastic sheet to the wall and that should actually work. Sealing all sides of individual bricks with silicone? Good luck with that.

Dook wrote:

Get some lego's, build a wall, overlap the blocks, take some silicone and seal the seams, let it dry, then try to blow through it.

You can try that at home. If you ever get a structure the size of a shoebox to hold 1 atm, let us know. Hell, let NASA know. They'll be interested if you can do that and resolve the other problems I noted.

Dook wrote:

What happens if your inflatable ruptures? Does it collapse onto the crew? How do you fix it?

Humans would be rendered unconscious in seconds if their pressure vessel ruptured and would die shortly thereafter. However, fabric and aluminum pressure vessels tend to leak in predictable places. In a large structure built from thousands of bricks with thousands of crevices, how would you know where to start looking for the leak?

Dook wrote:

No company you know of has ever constructed a pressure vessel built out of lego blocks? How many of them have built habitats on Mars before?

If we can't get this concept to work here on Earth, does it matters how much money is spent transporting an impractical or unworkable solution to another planet?

Dook wrote:

So an inflatable is better than structural blocks?

A cylindrical pressure vessel is better than a square pressure vessel, if the goal is to reliably hold substantial pressure over relevant time periods. The use of inflatables has a lot to do with weight, in comparison to metal cylindrical pressure vessels, and deflated packaging volume.

Dook wrote:

No sealant and plastic bag is going to withstand the force of one atmosphere for very long? You said it. Talk some sense into these people who want to use inflatables to live in forever on Mars.

Kevlar and GFRP are markedly different materials with different mechanical properties. Sarcasm won't change that.

kbd512 · 2016-11-03 03:23:49

Dook,

Maybe it's just mis-communication, or perception on my part, but from your responses I feel as though you take some of this as some sort of personal attack. If I'm coming across that way, I apologize, as that was not the intent.

Some of the ideas you've come up with have been pretty good concepts. Going from ideation to instantiation runs smack into physics and mathematics. At that point, you have to do a bit of homework to determine just how feasible any particular idea is.

My responses to you are intended to illicit responses directed towards the feasibility of your concepts and either offer alternatives that might work or figure out how you intend to go about doing something. A lot of this is just looking up masses, dimensions, material mechanical properties, etc.

1 atm = ~14.7psi (pounds per square inch)

A column of water 1 square inch in area and 33 feet in depth weighs 14.7 pounds. It takes 33 feet of water to hold back 14.7psi. That 14.7 pounds worth of water doesn't weigh 14.7 pounds on the surface of Mars, either. It's more like 5.6 pounds and that means even more water is required to apply enough force to hold back 14.7psi. When a vessel is pressurized, there is indeed that much force being exerted on the interior of that vessel. If the only thing holding the walls of the vessel together is mechanical counter-pressure, then something has to apply that much counter-force or whatever was pressurized within a vessel otherwise incapable of withstanding the outward force applied to its walls is going to escape.

The atmospheric pressure on the surface of Mars is only .087psi.

Martian regolith's bulk density is roughly 1.52g/cm^3, therefore 1 cubic inch (16.3871 cubic centimeters) weighs 24.9g.

We could vary the water content of the regolith and get greater or lesser Martian regolith bulk densities, but what we're talking about holding back should be pretty clear at this point.

JoshNH4H · 2016-11-03 08:14:19

kbd512,

I think you might be a bit too much down on using regolith to contain pressure in the vertical direction. Gravel and sand combined have a density of about 2,000 kg/m^3. Bricks probably have a density closer to 2,500 kg/m^3 or 3,000 kg/m^3. To contain 1 atm with those materials on Mars would require 13.5 m, 10.8 m, or 9.0 m of material, respectively. Depending on composition, lower pressure atmospheres can also be breathable. 50% of an atmosphere only requires 6.8 m, 5.4 m, or 4.5 m respectively. That's not really all that much.

It's true that piles of sand and gravel are generally not cylindrical, but it's pretty trivial to build a wall around the pile to prevent it from spreading out. If you'll notice, one was included in my drawing of such a habitat. Bricks or concrete of course are very easy to form into a cylindrical shape.

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