Domed habitats... - ...size, materials, and more.

Byron · 2002-07-20 06:47:59

I have a question about the construction of large-scale domes... Assuming we've managed to lick the problem of building footings capable of anchoring the dome to the ground, what about the "floor" of the dome itself? Would it be necessary to strip off the first couple of meters of regolith and lay down a slab of concrete, and put the regolith back on top of it? I'm just thinking that the extreme air pressure (compared to the native environment) would force its way through the ground under the dome and cause unacceptable rates of leakage.

Another idea I was toying about domes in my head, is the construction of an entire sphere, with the bottom portion flattened into a concave shape, with most of the exacavated regolith dumped back down on top of it to create a relatively flat floor. This would create a completely enclosed and sealed environment, and we wouldn't have to worry about attempting to attach the sides of the dome walls to the steel rail along the surface...as that would create a great deal of "pull" along the perimeter. With a completely enclosed sphere, the pressure would be spread out much more evenly, mitigating the extreme "pressure points" you would have with a dome attached to a perimeter footing.

I know this would involve moving around a tremendous amount of dirt, but might this be easier than producing and pouring 7,000,000 cubic meters of concrete (and which would still involve moving around a good deal of dirt as well)? I've heard that activities such as excavation and moving regolith will be "easier" on Mars than here on Earth, as the low gravity causes it to be compacted more loosely than terrestrial dirt, and therefore making it less troublesome to move it around. There's also the option of using huge amounts of explosives to "relocate" large volumes of regolith as well. In addition, the Martian engineers could take advantage of Martian topography to site this "lifesphere" (don't know what else to call it..lol), such as a crater or those nicely rounded, concave cliffsides you see in those amazing images of Candor Chasma and other locations. (Just imagine the view from a place like that!) Just an idea, anyhow...

B

Phobos · 2002-07-20 15:56:52

I have a question about the construction of large-scale domes... Assuming we've managed to lick the problem of building footings capable of anchoring the dome to the ground, what about the "floor" of the dome itself? Would it be necessary to strip off the first couple of meters of regolith and lay down a slab of concrete, and put the regolith back on top of it? I'm just thinking that the extreme air pressure (compared to the native environment) would force its way through the ground under the dome and cause unacceptable rates of leakage.

If your going to pour a slab a km squared in area, you'll probably have to excavate down a good distance and then pack the hole with fill dirt and grade it until it's perfectly even before pouring concrete. You could pour the foundation directly on top of rock, but I doubt if your going to find a continous and even slab of rock that's a km squared unless you dig very deep. I'd hate to be the compaction tester on that job, since without optimum moisture in the soil you won't be getting good compaction. Now that I think of it, you could fill the slab in with pure crushed rock and vibrate the rock. No moisture needed to get compaction there as long as the rock isn't ground into a powder.

I know this would involve moving around a tremendous amount of dirt, but might this be easier than producing and pouring 7,000,000 cubic meters of concrete (and which would still involve moving around a good deal of dirt as well)? I've heard that activities such as excavation and moving regolith will be "easier" on Mars than here on Earth, as the low gravity causes it to be compacted more loosely than terrestrial dirt, and therefore making it less troublesome to move it around. There's also the option of using huge amounts of explosives to "relocate" large volumes of regolith as well. In addition, the Martian engineers could take advantage of Martian topography to site this "lifesphere" (don't know what else to call it..lol), such as a crater or those nicely rounded, concave cliffsides you see in those amazing images of Candor Chasma and other locations. (Just imagine the view from a place like that! Just an idea, anyhow...

I supposed if you dug down say five meters and then graded and packed the soil in with very high compaction, say 95%, you might be able to forgo your concrete slab. But it's going to be damn near impossible to get 95% compaction on Mars, it's difficult to get that here on Earth where heavy equipment and water abound. That low Martian gravity is a double edged sword, it'll make it easy to dig up the regolith, but it's going to make it difficult to compact it properly, especially since Mars isn't friendly to liquid water. I'm wondering if there might be something in between, something more durable than just a soil foundation, but less work than a concrete one. Something that you could just pave like asphalt comes to mind, but you'd have to find an alternative that doesn't use oil. Your ideas for a half-filled sphere would probably be easiest to pull off provided the materials were strong and wouldn't decay under the pressure of all that regolith. Not sure you could build one a kilometer in diameter though.

RobS · 2002-08-08 00:05:40

Fascinating discussion about constructing domes. Zubrin's *Mars Direct* assumes that concrete is not necessary, though. One can bury the skirt of a hemispheric dome with regolith and that is enough to counteract the atmospheric pressure. The key is to find the right regolith. For example, there are several former lakebeds that have been located from orbital photography. Their composition is probably layers of fine clay with water-ice still present at depth. Such lakebeds would provide ready water supplies (you'd drill a well and add reactor heat, for example) and uniform, soft materials for excavation. Presumably one could erect a dome in such a material simply by using construction equipment to excavate a circular trench of adequate size, place the dome and its skirt, then backfill. If you want more stability, one could drive steel pylons into the lakebed. All that could be accomplished using machines driven by men without spacesuits.

Air will initially leak out of the dome by perculating through the clay underneath. But you could inflate the dome with Martian air for a few months and add water vapor. The water would perculate into the ground and freeze up the cracks, eventually producing a block of ice underneath the warmed ground. The domes might be leaky, but photosynthesis possibly would produce oxygen faster than the leaks, too. If one surrounded a dome with other domes, the growing colony would only leak air at its periphery, and many domes, surrounded by other domes, would produce surplus oxygen for maintaining the colony's supply.

Terraforming might weaken such domes, but if the temperature on Mars rose enough to weaken permafrost, it would only be after the atmosphere thickened significantly anyway. Under those circumstances the domes would need less mass to hold them down and the differential pressure would be less, leading to smaller leaks.

Since terraforming will most likely take centuries, the earliest domes can always replace concrete with a water and clay mixture if anything strong and hard (and airtight) is needed. Injecting water into the ground around a dome, forming an ice curtain, may be the best way to prevent subsurface air leaks.

-- RobS

Phobos · 2002-08-08 20:41:51

Great ideas about using frozen water to seal up cracks. Using the "artificial permafrost" around the periphery of the dome to help seal it up sounded good to. On the inside of the dome you could just hydrate and compact the soil in order to create building pads for brick structures since brick would be extremely easy to manufacture on Mars.

EuroLauncher · 2006-01-18 09:51:41

some more more info here

http://www.permanent.com/s-future.htm
http://www2.ville.montreal.qc.ca/biodom … ?langue=en

http://isecco.org/projects/celss/m_index.html
http://www.biospherics.org/resbio2labglobecol.html

Rxke · 2006-01-18 13:52:55

A new record for thread-necromancy!

*ducks*

canalbuilder2 · 2006-01-25 10:36:19

There's life in the old beast yet.

The ice used to plug the holes and cracks can be significantly strengthened by the addition of a binding agent such as sawdust. It shouldn't melt as long as people don't build fires on it. It's a piece of world war two technology called pykrete.

http://www.combinedops.com/Pykrete.htm

or wikipedia.

In a previous incarnation I suggested it could be used to build the actual domes, but I can't remember where I put that comment.

Rxke · 2006-01-25 12:17:20

In a previous incarnation I suggested it could be used to build the actual domes, but I can't remember where I put that comment.

Yes, I remember that...

BTW, the thread-necromancy is good for one thing: I'm constantly amazed at the quality of some threads that seemed to fizzle out for no good reason...

Tholzel · 2006-02-06 10:30:57

Josh Cryer wrote:

One thing that's different about Mars is that there isn't any soil. Our buildings would literally rest on bedrock, except where sandstone predominates. Compaction is necessary when something rests on something. But domes will have to be secured to the ground, much like a tent. Tents don't rest on the ground, they kind of pull away. So the trenches may have to have adjacent underground holes inside of them, to help us secure the domes to the ground. It's hard to picture, and hopefully I'll have some illustrations up soon.

But in order to breathe without a space suit, you would need at least, say, 5psi of pressure--and even that low presure would require a high--dangerous (fire, explosive) concentration of oxygen--around 35% (instead of earth's 21%).

How is this pressure going to be retained? Certainly not with any simple structure. And even "bedrock" does not seem hermetic enough. So the entire dome would require an air tight floor.

Suddenly the dome becomes much more complicated.

My solution is to forget human habitation in our life-times (I know, boo-hoo.) Instead, send teams of construction engineers to rig huge sail-like covers of lexan sheets to cover small channels. These football-sized (and even much larger) sheets would protect the ground from deadly UV radiation, and thus give any deposited plant-life a chance to grow. That would be a start, and if successful, this new plant life (fungus, whatever) would be free to adapt to the martian environment outside of the sheets.

Commodore · 2006-02-19 00:27:39

Some really interesting stuff here. I think its good to rehash some of these once in a while.

Anyway, it was mentioned long ago and strikes me as a great idea, and that is to use existing craters to provide the basis for your dome walls and supports.

Basically you pick a crater about 200-300m across with a good solid rim. Then you dig all the dust and regolith out of the bottom so that you’re down to solid bedrock and have as nice a bowl as you can get. Next, in the very center drill into the bed rock and put down pylons, and pour a center start point several meters across. Now you build a turn style on that concrete pad and several sets of round rail lines at intervals all the way out to just outside the rim and on these there will be a series of cranes. Now you can start dropping in pre-poured concrete blocks in a circular pattern from the center. Your crane, like those used to load trailers on to railroad cars, only much longer, could receive loads as big as the pre-pours blocks from outside the rim. It would be a lot like building an upside down igloo. You can have thicker sections were appropriate to have additional levels. Steel pylons protrude straight up from below to support these levels. Blocks are interlocked and cemented together. At the same time supports for the dome are dug in outside the rim. A tower goes up in the center to support the center of the dome, and with elevators of varying sizes, and they eventually meet at roughly 45 degrees as the floor is completed. The goal is to cover and pressurize as soon as possible to allow as much of the work to be done in shirt sleeve environment as possible. Ultimately you'll have several story’s of pressurized space for industrial, agricultural, scientific, and residential purposes, as well as several acres of pressurized open space.

As for when this is possible, I would say by the end of the century as the culmination of several decades of effort, even though actual construction should only take a few years. I picture a series of as many as a dozen smaller bases of 25-50 people put together by several nations in the 2050-2075 range, inhabited by government quasi-colonists who follow directly behind the astronauts. Hopefully by then similar efforts on the Moon will lower the costs to a point were this is affordable despite the distance. Together theses folks should be able to do a "complete" survey of the planet, and build preliminary infrastructure to provide global access from any one point on the ground. Then working together the above described mini city of several thousand can be built, and colonization and terraforming can begin in ernest.

Rxke · 2006-02-21 03:59:23

How is this pressure going to be retained? Certainly not with any simple structure. And even "bedrock" does not seem hermetic enough. So the entire dome would require an air tight floor. .

Pipes/drills pumping down hot water, it will freeze out, permafrost might be a good seal. With self-sealing properties to boot.

Might. But then again, if you would be able to produce enough water to do that, (I mean, have the infrastructure, and power) you arguably would have a way to replenish some losses.

(EDIT: ugh, RobS, as usually, has the same idea, but better, posted in this thread on August 8,2002. That's what you get, digging up ancient topics, heehee...)

Grypd · 2006-02-22 07:49:16

Some really interesting stuff here. I think its good to rehash some of these once in a while.
Anyway, it was mentioned long ago and strikes me as a great idea, and that is to use existing craters to provide the basis for your dome walls and supports.
Basically you pick a crater about 200-300m across with a good solid rim. Then you dig all the dust and regolith out of the bottom so that you’re down to solid bedrock and have as nice a bowl as you can get. Next, in the very center drill into the bed rock and put down pylons, and pour a center start point several meters across. Now you build a turn style on that concrete pad and several sets of round rail lines at intervals all the way out to just outside the rim and on these there will be a series of cranes. Now you can start dropping in pre-poured concrete blocks in a circular pattern from the center. Your crane, like those used to load trailers on to railroad cars, only much longer, could receive loads as big as the pre-pours blocks from outside the rim. It would be a lot like building an upside down igloo. You can have thicker sections were appropriate to have additional levels. Steel pylons protrude straight up from below to support these levels. Blocks are interlocked and cemented together. At the same time supports for the dome are dug in outside the rim. A tower goes up in the center to support the center of the dome, and with elevators of varying sizes, and they eventually meet at roughly 45 degrees as the floor is completed. The goal is to cover and pressurize as soon as possible to allow as much of the work to be done in shirt sleeve environment as possible. Ultimately you'll have several story’s of pressurized space for industrial, agricultural, scientific, and residential purposes, as well as several acres of pressurized open space.
As for when this is possible, I would say by the end of the century as the culmination of several decades of effort, even though actual construction should only take a few years. I picture a series of as many as a dozen smaller bases of 25-50 people put together by several nations in the 2050-2075 range, inhabited by government quasi-colonists who follow directly behind the astronauts. Hopefully by then similar efforts on the Moon will lower the costs to a point were this is affordable despite the distance. Together theses folks should be able to do a "complete" survey of the planet, and build preliminary infrastructure to provide global access from any one point on the ground. Then working together the above described mini city of several thousand can be built, and colonization and terraforming can begin in ernest.

One problem with using concrete as the Biosphere 2 crew discovered is as it hardens it absorbs air. In there case it caused a lot of problems to the point it was hazardous and extra air had to be put in. Of course this extra air began to be absorbed as well. So concrete is a problem as well as possibly taking a long time to harden and being slightly porous even with sealant materials over it.

One option is once you have cleaned out the crater we then backfill it with regolith that has been sorted to ensure it is very highly Iron enriched. This is then heated and the Iron regolith melts to form a single surface of non porous Metal concrete glass. If this is then used as the base to put a smaller layer of concrete on top air reduction will be a lot less and the dome would have a very hard stable base. Especially if secured points where emplaced before the operation started.

Using permafrost is useful for initial bases but if we are to succeed on Mars then we are going to terraform and anything built on permafrost is the equivalent of building on sand.

Rxke · 2006-02-22 08:54:35

As I remember it, it didn't merely absorb air, but reacted w/ the oxygen in the atmosphere, slowly depleting oxy levels, causing the people inside to feel exhausted constantly.... Climbing stairs was a massive effort, they had to pause two or tree times to take a flight of stairs (!) The reaction-losses were significant, no wonder because of the surface of exposed concrete. Took awhile before they figured out what was happening. They kept pumping in emergency-oxy, and seeing levels drop again and again...

Rxke · 2006-02-22 08:59:46

Using permafrost is useful for initial bases but if we are to succeed on Mars then we are going to terraform and anything built on permafrost is the equivalent of building on sand.

By the time you're melting the permafrost planet-wide, you have other concerns, atm. pressure will rise very significantly long before that happens, and you'll end up by building another type of domes, I guess. By that time the original domes will be truly ancient, and there will be a good-sized industrial basis to allow you to build more complex enclosures etc.

I think RobS's idea is a good one, that will last its time, until mass production etc. is well established.

EDIT: (To quote RobS (again, heehee)

Terraforming might weaken such domes, but if the temperature on Mars rose enough to weaken permafrost, it would only be after the atmosphere thickened significantly anyway. Under those circumstances the domes would need less mass to hold them down and the differential pressure would be less, leading to smaller leaks.

MarsDog · 2006-03-11 03:33:42

Yeah, that's why I asked if it was a hemisphere or a zone (hemisphere defined by height), a zone would take lots less material than a true hemisphere.

Material area might be less, but total force would be greater, therefore thicker material needed.
(divide the force by cosine of the angle between the sphere and spherical cap at the foundation)

http://physics.uwstout.edu/StatStr/stat … cols65.htm

Area =

http://mathworld.wolfram.com/Zone.html

================================

Most efficient use of material mass is a sphere.

swift99 · 2006-03-12 20:41:23

In the past, I have slam-dunked many ideas that involved using concrete on Mars. Lacking significant calcium bearing minerals, I did not think it was practical. However, a recent photo has change my view somewhat.

Compare these two mineral samples:

http://marsrovers.jpl.nasa.gov/gallery/ … R1_br2.jpg
and
http://ratw.la.asu.edu/RATW069/RATW06937_0.jpg

The laminar structure and flow patterns in the martian sample are sufficiently similar to the terrestrial flowstone sample that I am beginning to believe that we may be able to formulate a mars analog for terrestrial conrete, that would be mined, refined, and produced on site. This mineral would most likely be associated with "significant" volumes of water (in Martian terms), so the entire process would probably occur in the same mine.

Anyone know how to find out what the martian "flowstone" is composed of? I believe that they examined this with the IR Spectrometer.

canalbuilder2 · 2006-03-20 06:36:05

As I remember it, it didn't merely absorb air, but reacted w/ the oxygen in the atmosphere, slowly depleting oxy levels, causing the people inside to feel exhausted constantly.... Climbing stairs was a massive effort, they had to pause two or tree times to take a flight of stairs (!) The reaction-losses were significant, no wonder because of the surface of exposed concrete. Took awhile before they figured out what was happening. They kept pumping in emergency-oxy, and seeing levels drop again and again...

Concrete doesn't absorb air or react with oxygen. The problem is that carbon dioxide plays an essential role in the setting and curing of concrete. Although the concrete sets after about 28 days, it continues to cure (harden) for a very long time (years). This process takes carbon dioxide (and hence oxygen) from the atmosphere. I'm not sure at present what effects the reduced partial pressure of carbon dioxide on Mars would have on the concrete, but there might be a PhD in it.

In the Biosphere case, the oxygen shortage came about because the O2/CO2 balance was maintained as the CO2 was was removed.

Am I the only civil engineer here?

As mentioned before one of the other concrete quirks is that the setting reaction is exothermic. This means that concrete will always crack to some extent from uneven heating and cooling. The trick is to make sure that the cracks are minimised and do not pass through the entire structure. Traditionally this has been a problem for structures to hold aqueous liquids (dams, sewage tanks, etc.) When trying to hold back the atmosphere inside a dome, I think it might be necessary to use a geotextile membrane. I like the idea of thawing and refreezing water to make the seal, but I'm not sure about the quality control.

C M Edwards · 2006-03-20 08:44:27

In the past, I have slam-dunked many ideas that involved using concrete on Mars. Lacking significant calcium bearing minerals, I did not think it was practical.

If calcium is rare, then don't use it as a structural material. It's required for portland cement, true, but there are many other cement blends available. Sorel cement, for example, is a magnesia cement - a cement that uses magnesium oxide rather than calcium oxide to produce a binder. It has about the same strength as portland cement, has a similar mix, and is produced using a similar process. I'm not saying you just hold the quicklime out and throw the magnesia in to make sorel cement instead of portland cement, but it's darn close.

We've found precious little magnesium carbonate on Mars so far (or anything carbonate, for that matter... :? ), but there is clearly magnesium everywhere over there. If you're just willing to forget about portland cement, you can have concrete on Mars.

swift99 · 2006-03-20 20:13:41

If you're just willing to forget about portland cement, you can have concrete on Mars.

You will want a Mars analog, but its formulation will be quite different. The Eco-cement appears, on the surface, to be a good starting point.

Am I the only civil engineer here?

Possibly. My construction experience is on the contracting end, not the engineering.

I think a plastic sealant would be a better choice than water or geotextile. The temperatures can sometimes get (barely) above freezing on Mars, and water is likely to be a rare commodity for a while. Most geotextiles are too porous to form a suitable seal for air containment.

canalbuilder2 · 2006-03-21 03:38:41

I think a plastic sealant would be a better choice than water or geotextile. The temperatures can sometimes get (barely) above freezing on Mars, and water is likely to be a rare commodity for a while. Most geotextiles are too porous to form a suitable seal for air containment.

The plastic sealant is a good idea. What happens in some liquid retaining structures is that when the concrete is poured channels are formed in the surfaces at predetermined distances. These channels are where the cracks will from. After the concrete has set, a sealant (either silicone or tar based) is fixed into the channel.

An alternative method is to include an impermeable membrane in the concrete to intercept your designed cracks. Some of the modern geotextiles are impermeable to liquids and gasses. Particularly those used to protect us from the leachate and gas produced by landfill sites. The gas can be used for fuel, but that's a different matter.

My idea for using water as a sealant relies on using it in its liquid state to penetrate cracks in the rock that our dome will be built on. Then when it freezes, it will, I hope, form an impermeable barrier. As with the concrete the problem will be cracking as the water freezes. Of course, there is the added matter of the water expanding.

Ed

Gregori · 2008-01-13 22:30:32

Perhaps it could be sealed better if the structure was a giant metallic sphere? The bottom half of the sphere could be submerged in the regolith.

The top half of the structure would use a lattice of plastic plates (or any suitable transparent material) reinforced by a welded metal frame.

The material to build this could be mined from an Iron rich asteroid.

MarsRefresh · 2008-01-19 11:22:15

Perhaps it could be sealed better if the structure was a giant metallic sphere? The bottom half of the sphere could be submerged in the regolith.
The top half of the structure would use a lattice of plastic plates (or any suitable transparent material) reinforced by a welded metal frame.

The material to build this could be mined from an Iron rich asteroid.

This certainly would be strong, but I fear that the cost and effort involved would prove prohibitive. I favor pressurized plastic domes with a exterior, unpressurized steel lattice abrasion shield in which plastic panels can be periodically switched out as they break down under UV and wind erosion.

Terraformer · 2008-01-19 15:22:51

A mesh of rubber/plastic pipes that are filled with high pressure water? The water will keep the dome stiff and provide radiation protection. Wait, Bigelows probably thought of that for inflatable spacecraft.

MarsRefresh · 2008-01-20 11:11:07

A mesh of rubber/plastic pipes that are filled with high pressure water? The water will keep the dome stiff and provide radiation protection. Wait, Bigelows probably thought of that for inflatable spacecraft.

I think you would be trading a lot of visibility and such a system would be very difficult to maintain.

I like the idea of water as UV protection, but I haven't seen a good way to use it in domes. (I'm also strongly in favor of a single pressure layer for the sake of simplicity.)

Terraformer · 2008-01-20 12:02:12

Clear tubing, filled with clear water?

Wait, that would refract the light, so it might be possible to design it to focus more light in...

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#26 2002-07-20 06:47:59

Re: Domed habitats... - ...size, materials, and more.

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