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

Josh Cryer · 2002-01-07 11:23:21

Can anyone think of any problems we would face with domes? What kind of domes should we build? How do we build them? Does anyone think domes are too grandiose for our needs? When do we start using them? When we get there initally or when the first real pioneers get there? Should we take dome material or should we create it there? Why kind of habitat would a dome be like? How big should our largest domes be? How many people can they hold? How about the smallest ones?

This, and many more. Let's discuss the pros and cons of domes. Let's discuss when they'll be used (and argue whether or not they will ever be used at all), and let's figure out exactly why so many people are hyped over domes.

Phobos · 2002-01-08 00:21:44

One of the reasons I like domes is that they seem to be the easiest way to encapsulate large areas of land. I imagine they'd also be more efficient at keeping air inside instead of allowing it to leak out. Not only does it seem like it would be more work to build extremely large "brick and mortar" type structures, but despite all the caulk you take along, they'd probably require more energy to keep the atmosphere up to specs due to leakage. I think a combination of the two is the best since the vault-like buildings could end up being necessary to protect colonists from radiation (would that be a problem on Mars?) Then again I guess you could just take prefabricated buildings parts and assemble them.

Josh Cryer · 2002-01-08 02:12:39

Good point, they are great for enclosing large areas of land, and less susceptible to leaks than say, an underground habitat. Though getting the domes to be completely secure to the ground (or over a crater) will prove difficult initally. I remember as a kid digging fence posts with an automatic digger, and I imagine the process would be similar, only you'd have to dig a trench all the way around and fill it with Martian-made concrete (every some yards having deep penetrating posts to really secure it).

If the domes had electricity running through them they would literally deflect most radiation, other things like UV coatings could help with the rest. It's quite a wonderful concept, really. In fact, domes would make more sense on the moon than Mars, since Mars actually has weather conditions (which could jepordize the dome, though honestly I don't think by much).

I think the one real argument for domes is simply that we'd be able to achieve things without tight cumbersom space suits. Each bubble could in fact be its own eco system, having the ablity to maintain itself completely without any outside resources (except for sunlight, perhaps). Domes are truely the first cities on Mars.

How's this for an idea:

What if we put strong plastic tracks on the outside of the domes (remember, once inflated they would necessarily be as hard as steel) to hold revolving solar panels? Sure, it would mean having shade inside the dome in certain areas, I think this could work. Would it help us much, though? Probably, in the beginning, when we have limited solar panels and must maximize light absorption.

Lil_vader · 2002-01-08 14:02:23

It might also help if we put the domes in the bottom of a large crater and had solar panels arrayed on the sides of the crater. Solar panels reflect a lot more light than they absorb, so the reflected light could be used to help warm the dome.

Phobos · 2002-01-09 22:36:37

Good point, they are great for enclosing large areas of land, and less susceptible to leaks than say, an underground habitat. Though getting the domes to be completely secure to the ground (or over a crater) will prove difficult initally. I remember as a kid digging fence posts with an automatic digger, and I imagine the process would be similar, only you'd have to dig a trench all the way around and fill it with Martian-made concrete (every some yards having deep penetrating posts to really secure it).
If the domes had electricity running through them they would literally deflect most radiation, other things like UV coatings could help with the rest. It's quite a wonderful concept, really. In fact, domes would make more sense on the moon than Mars, since Mars actually has weather conditions (which could jepordize the dome, though honestly I don't think by much).
I think the one real argument for domes is simply that we'd be able to achieve things without tight cumbersom space suits. Each bubble could in fact be its own eco system, having the ablity to maintain itself completely without any outside resources (except for sunlight, perhaps). Domes are truely the first cities on Mars.
How's this for an idea:
What if we put strong plastic tracks on the outside of the domes (remember, once inflated they would necessarily be as hard as steel) to hold revolving solar panels? Sure, it would mean having shade inside the dome in certain areas, I think this could work. Would it help us much, though? Probably, in the beginning, when we have limited solar panels and must maximize light absorption.

Good point, they are great for enclosing large areas of land, and less susceptible to leaks than say, an underground habitat. Though getting the domes to be completely secure to the ground (or over a crater) will prove difficult initally. I remember as a kid digging fence posts with an automatic digger, and I imagine the process would be similar, only you'd have to dig a trench all the way around and fill it with Martian-made concrete (every some yards having deep penetrating posts to really secure it).

I think your ideas about digging a giant trench several yards down to anchor the dome is extremely practical. It's similiar to digging out footings for buildings. I think one of the unseen difficulties of Martian construction is ensuring that these trenches, and especially the building pads for brick and mortar type structures, have proper compaction. In California building pads are usually required to have 90+% compaction and just getting that usually requires that the soil have a very precise amount of moisture (not too much not too little) and a lot of work with heavy compacting machinery. I doubt if running over the raw soil a few times with your rover is gonna cut it, but on the upside, Mars has less gravity so having ultra high compaction requirements might not be necessary.

I think the one real argument for domes is simply that we'd be able to achieve things without tight cumbersom space suits. Each bubble could in fact be its own eco system, having the ablity to maintain itself completely without any outside resources (except for sunlight, perhaps). Domes are truely the first cities on Mars.

I think this is the best argument for domes. I can't imagine always being holed up in some tiny structure somewhere and, even though it sounds corny, I think it'd be a trip to run barefooted across the surface of Mars. Yeah I know, you could always build some tiny courtyard in another kind of structure, but domes by far seem the easiest way to make large tracts of land available without needing a spacesuit.

Josh Cryer · 2002-01-10 02:16:38

I think your ideas about digging a giant trench several yards down to anchor the dome is extremely practical. It's similiar to digging out footings for buildings. I think one of the unseen difficulties of Martian construction is ensuring that these trenches, and especially the building pads for brick and mortar type structures, have proper compaction.

Thanks. I think they're pretty intuitive myself. But I'm not sure how we'd go about inflating the dome, if it would be made of strips that were sewn and glued together, or if it were one large tent like some carnivals have. One sewn together (with various plastics) would not be structurally deficient, but one completely premade would be a huge project to deploy.

When we unfold one that is completely sewn together we have to account for the surface area and volume. And keeping it from dragging around on the ground is going to be a tricky thing to pull off, too.

Strips wouldn't suffer from the ?holy crap, this thing is huge? syndrom, but they'd be complicated to put together. Securing them to the ground would be easy, but aligning them and sewing them together would be very hard.

There really is no win-win with deployment. At least, not at first. We've never done anything like that before.

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.

I think this is the best argument for domes. I can't imagine always being holed up in some tiny structure somewhere and, even though it sounds corny, I think it'd be a trip to run barefooted across the surface of Mars. Yeah I know, you could always build some tiny courtyard in another kind of structure, but domes by far seem the easiest way to make large tracts of land available without needing a spacesuit.

I totally share your sentiment. And anyway, we're talking about homes, not science stations. I had a dream the other night that I was sleeping in a hammock inside of a dome under a clear night sky. It wasn't as transparent as I would have wanted, but I could still make out Earth and Phobos. Kind of a cool thing that probably won't be realized in my lifetime.

Phobos · 2002-01-12 13:00:12

Thanks. I think they're pretty intuitive myself. But I'm not sure how we'd go about inflating the dome, if it would be made of strips that were sewn and glued together, or if it were one large tent like some carnivals have. One sewn together (with various plastics) would not be structurally deficient, but one completely premade would be a huge project to deploy.

The only way I can think of to inflate a dome would be to use powerful aircompressors, particularly if its very large. One of the problems I wonder about is how to insure that the you have the proper ratio of oxygen, etc, if you compress the air directly out of the Martian atmosphere. I guess once you set up the proper air pressure you could introduce plant life into the dome to process the atmosphere, but it seems that if you want the dome to be inhabitable the instant you build it you'll have to bring along a giant aerosol can full of the proper air mixture you need. In addition, since these aircompressors will probably have to always be working to compensate for leakage, it seems you'll have to insure that they don't poison the air with excess carbon dioxide. As far as whether to use strips or one giant sheet of material to build the domes out of, I think strips would be the most practical way since, like you said, it would be difficult to manufacture and handle a giant sheet of material especially if your going to build something large enough to house an entire town. I think with the use of epoxies and sealants the strips could be made nearly as leakproof as if you had one giant sheet composing the dome.

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.

I didn't realize Mars was mostly bedrock. Yeah, that would definately make compaction a mute point. I had often wondered about soil on Mars given that it hasn't had 5 billion years worth of abundant life living and decomposing on its surface. I think I see what you mean about the adjacent holes inside the perimeter of the trenches to keep the dome
staked to the ground. I had often thought that a way to build domes would be to build a light weight frame on which to tack strips of the enclosing materials, something similiar to a tent frame.

I totally share your sentiment. And anyway, we're talking about homes, not science stations. I had a dream the other night that I was sleeping in a hammock inside of a dome under a clear night sky. It wasn't as transparent as I would have wanted, but I could still make out Earth and Phobos. Kind of a cool thing that probably won't be realized in my lifetime.

I like that image of laying back on a hammock and looking up into the night sky to see Earth and the moons. I imagine Earth would appear to be a bright blue star. Would you be able to see both Deimos and Phobos at the same time? Since you mentioned only Phobos, I kinda get the feeling my question has already been answered.

RobS · 2002-01-16 16:15:37

I have a few thoughts about domes that might help one visualize them. Zubrin's book on Mars Direct notes that a 100-meter in diameter sphere of kevlar (one of the strongest and toughest plastics ever developed) would weigh 64 tonnes. A hemisphere (half a sphere) would therefore weigh 32 tonnes. It would enclose 7854 square meters or .7854 hectares, which is about two acres. Its volume would be 2/3 pi r3 or 261,800 cubic meters. Since the mass of air at a third of an atmosphere of pressure is about half a kilogram per cubic meter, the air inside would weigh 130,000 kg or 131 tonnes. The reactor Mars Direct postulates could make that much oxygen from CO2 in less than a year.

Another useful statistic: the suface area of a hemisphere is 15,708 square meters. Each square meter, at a third of an atmosphere of pressure, will have about 3.3 tonnes of force on it (33,000 newtons, if you are a purist), so the dome will have an upward force on its outer edge of about 50,000 tonnes. The perimeter is 314 meters long, so that's an upward force of 165 tonnes per meter. If you assume a ten meter wide sleeve on the ground and Martian rock "weighs" about a tonne per cubic meter (the mass is about 2-2.5 tonnes per cubic meter, but the weight is that times Martian gravity, 0.38) then you would have to bury the sleeve under 16.5 meters (54 feet) of dirt and rock to hold it down. You could also anchor stakes in the regolith to help hold it down, reducing the dirt pile to some extent. The obvious place to put housing is under the dirt pile perimeter, so that the housing opens onto the interior space and the regolith reduces cosmic ray and solar radiation exposure to almost terrestrial levels. It's amazing you can do all that with 32 tonnes of kevlar and a bulldozer!

The floor probably should have plastic liner to help make it air tight; on top of that you'd pile processed Martian regolith. You'd want to build the dome somewhere there are ample supplies of eolian drift and clay. The big problem probably is desalting the regolith, though you might find regolith with low enough salt levels so that you don't have to desalt it for plants to grow in it. You'd have to add nitrogen and maybe phosphorous.

A landscape architect friend of mine who was designing a rooftop garden once told me you put 9 inches (23 centimeters) of dirt on a rooftop garden. That would take about half a tonne of soil per square meter, or 15,000 tonnes total. That would take machinery quite a long time to prepare; probably a year or two. Meanwhile, you could get away with less and start on one side of the floor only.

Biosphere 2, in Arizona, had an intensive agriculture area of 2233 square meters that was able to feed eight volunteers inside. Thus this hemisphere could feed about 24 people. Presumably any Mars station building such big enclosures would have several, in case one were temporarily damaged, so a 100-meter hemisphere would be built by stations of 100 or so people.

What shape would you like the dome's floor to take? It could be flat, but probably you want it sloping to a low point for drainage. The obvious thing to do would be to put a pond somewhere at the lowest point--maybe in the middle. You'd raise fish in the pond, flood a rice paddy next to it, swim in the pond for fun, and have a small barbeque patio there as well. A barbeque would put a lot of smoke in the interior, but not a dangerous quantity (assuming you had all 261,000 cubic meters of air space inside).

The dome would probably be layered; in other words, instead of one dome, you'd want a minimum of two, maybe three or four, nested inside each other. That way if one leaks the air just leaks out to the next dome, an alarm goes off, and someone has to go find the leak and fix it. If you had three or four domes, the spaces between the others could be used to store nitrogen, argon, and other inert gasses you might want to use for other purposes. Multiple domes also are essential for insulation against the frigid exterior temperatures.

I am guessing, but you may also want to draw a black insulating shroud over the dome at night to hold in the heat. If that is the case, you'd have to have it retract if you wanted to look at the stars or moons. Maybe the computer could be programmed to pull the shroud over the dome every evening at 9 p.m., giving people two hours to look at the stars.

In the morning, you'd want to pull the shroud back on the east side only and leave the west side covered with the shroud, which would be silvered on the inside. This would reflect the morning light into the dome and increase total sunlight. With skillful computerized control of a silvered shroud over the outer dome, one could raise the total sunlight inside almost to terrestrial levels. In the afternoon, the shroud would cover the eastern side of the dome.

Josh Cryer · 2002-01-18 17:15:28

Hey RobS, how'd you come to your numbers? (Kevlar weight and such. And is your dome a perfect hemisphere, or a zone?)

I love all of your ideas, though I'm skeptical about how you're going to ship 15k tonnes of soil, we really ought to start working on Sax's soil alchemy.

RobS · 2002-01-19 00:38:04

The weights of the kevlar are all from Zubrin's *The Case for Mars,* page 178, where there is a section about domes. I was assuming a hemisphere when I gave volumes (formula, 2/3 pi r cubed).

As for processing the Martian regolith, there are various ways to do it. You might want to erect the dome over an area where you don't have to clear rocks, like an ancient Martian lakebed (there are a few; Zubrin mentions a "paleolake site" in passing in a chart on page 142). A lakebed might be mostly clay, which is easy to excavate, and it probably will contain permafrost or ice layers underneath. Rather than hauling the dirt in through airlocks after you erect the dome, you make a pile of dirt in the middle of your future dome first, build the dome around it, inflate it with compressed Martian air, then place the plastic "dropcloth" and bulldoze the dirt over it. The easiest way to get excess salts from the regolith, once it has warmed up and is in a pressurized environment, is to soak it with water, let the water run off, collect it, desalt it with reactor heat, and irrigate the regolith again. Zubrin says Martian regolith is pretty good in terms of minerals for plants (page 196). Adding nitrogen will be essential and the most difficult, unless the ancient Martian lakebeds include nitrate deposits (possible). My guess is that a good year of work by one or two people would be necessary to prepare the soil fully, but even slightly salty soil will grow some crops (the Israelis have been experimenting with salt-tolerant crops).

-- RobS

Bill White · 2002-01-20 17:12:12

RobS writes, in part, as follows:

<<. . . A (kevlar) hemisphere (half a sphere) would therefore weigh 32 tonnes. It would enclose 7854 square meters or .7854 hectares, which is about two acres. Its volume would be 2/3 pi r3 or 261,800 cubic meters. Since the mass of air at a third of an atmosphere of pressure is about half a kilogram per cubic meter, the air inside would weigh 130,000 kg or 131 tonnes. . . >>

Why do you need a full hemisphere?

Couldn't you shape the kevlar panels to lower the height at the center of the dome from 50 meters to maybe 20 meters?

From the outside, the dome would appear more like a 1/2 oval or 1/2 ellipse than a 1/2 circle. The ground level radius would stay the same at 100 meters, so you subtract volume and surface area but not "floor" area.

Obviously this would reduce the kevlar needed. It would also reduce the size of any rotating screen which was installed.

<< Another useful statistic: the suface area of a hemisphere is 15,708 square meters. Each square meter, at a third of an atmosphere of pressure, will have about 3.3 tonnes of force on it (33,000 newtons, if you are a purist), so the dome will have an upward force on its outer edge of about 50,000 tonnes. >>

Using a 1/2 ellipse rather than a 1/2 circle would also reduce the interior volume, without reducing the ground space. Would a reduced interior volume also reduce the "upwards" atmospheric pressure, thereby reducing the amount of rock and regolith needed to secure this thing to the surface?

Layers seem essential, for insulation and to minimize potential catastrophic de-pressurization, however, they also greatly reduce the amount of available sunlight needed to grow plants.

If some form of artificial light were used, you could grow plants on racks, with 2 or more "levels" per square meter of floor space, and double the amount of food that could be grown within the dome, but then it seems we are talking about nuclear reactors to power the light systems.

Josh Cryer · 2002-01-20 17:36:10

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.

RobS · 2002-01-21 00:37:37

Bill White makes some excellent points. Zubrin, in Case for Mars, also assumes that one would not use hemispheres, but "flatter" structures that do not go as high. I did my calculations with hemispheres because I do not know how to calculate volumes and surface areas of "flatter" structures. Zubrin said the thing to do is to use a portion of a sphere less than a hemisphere, like slicing the "top" or "bottom" off a globe.

Yes, a flattened hemisphere has less surface area and therefore would generate less upward pull, decreasing the amount of dirt needed to anchor a dome somewhat. Since I do not have the ability to calculate the area, I do not know what it will be. Consider that the surface area being domed over is a function of pi r squared but a hemisphere is 2 pi r squared. A flattened hemisphere would fall between those numbers, depending on the flattening.

Multiple layers do not have to decrease the available light. Zubrin says a 1 millimeter thick kevlar layer can hold in air at an entire terrestrial atmosphere of pressure. Let us say we divide the layer into four 1/4 millimeter thick layers, and let each layer approximate a true hemisphere more closely (rise higher and higher from the center of the enclosure). And let us assume that each layer holds in 1/4 of the total pressure underneath. A leak from the bottom layer into the next one would not necessarily exceed its yield strength if the layers were able to accommodate 2 or 3 times their standard design pressure, and by spreading the air out in a larger area the pressure on the second layer would be reduced anyway. Presumably 4 layers 1/4 mm thick block as much sunlight as 1 layer 1 mm thick.

As for multiple levels of plants, this assumes artificial lighting, which assumes an ample source of energy. The surface of the earth receives over 1 kilowatt of sunlight per square meter, constantly during the day. On Mars that is already reduced to less than half, which is a problem for some plants (some vegetables and grains do not grow well when they get only six hours of sunlight per day. I know; my backyard garden is partially shaded). A dome with multiple levels of plants reduces their light exposure even more. If you have to supplement 10,000 square meters of plants with artificial light, you may need 10,000 kilowatts of power to do it! It's easier to spread the plants out under domes and use mirrors to give them some extra light.

-- RobS

Shaun Barrett · 2002-01-29 01:05:52

You can always count on RobS to come up with a bunch of interesting figures and ideas! And nicely expressed, too ... I could almost imagine myself in the bulldozer!
I don't pretend to be an engineer and I freely confess to having forgotten most of the mathematics I learned in school, but I'm going to stick my neck out here and ask a question which may brand me as a half-wit!
In RobS's highly absorbing discourse on the kevlar dome (the 100m hemispherical one), he says:"so the dome will have an upward force on its outer edge of 50,000 tonnes." This is obviously derived from simply multiplying the surface area of the hemisphere, 15,708 sq.m, by the pressure, 3.3 tonnes per sq.m.
Is this actually correct? Surely some of the pressure is acting sideways; most obviously where the dome approaches the ground. This sideways pressure is balanced by the air pressure pushing in the other direction on the dome wall diametrically opposite. As you climb the dome wall, it gradually becomes less vertical and more horizontal, and the force vectors on the dome become stronger in the upward direction. (Stop me if I'm making a fool of myself!)
It seems to me, relying on intuition in order to avoid vectors and calculus(!), that the actual total vertical force vector is more likely to be equal to the surface area of the ground multiplied by the pressure. i.e. 7854 times 3.3, or 25,918 tonnes. Any competent mathematician out there should be able to verify this ... or shoot it down!
If I am not mistaken, the upward pressure on any dome shape will therefore be independent of the actual curvature of the dome and dependent solely on the ground area enclosed.
Also, if I'm right, we won't have as much trouble preventing the damned thing blowing away like a party balloon!!
Any thoughts?

RobS · 2002-01-30 16:02:06

You may be right about the pressure calculation. If you are, think of my calculation as a way of figuring a maximum force we must deal with in planning a dome.

I should add that my information about available sunlight needs some correcting. While the Earth receives slightly more than twice as much sunlight per square meter as Mars, our hazy atmosphere absorbs some and our clouds reflect a lot. As a result, crops are generally relying on a total incoming sunlight not much greater than available on the surface of Mars. I have seen a figure in a space colonies book I have lying around somewhere and can post it in a few days. As a result, the use of some mirrors to reflect even more sunlight into a dome could allow some multiple levels of plant life. Maybe one could get 50% more surface area that the flat surface might suggest. That could be very helpful.

Somewhere I mentioned that biosphere 2 (you must go see it if you haven't; quite interesting) allocated 280 square meters per person for agriculture. Thus a 100 meter dome, if it has a 10 meter wide skirt for burying and thus 80 meters in diameter of open space, would have about 5,000 square meters of area and that would be able to feed about 18 people. One thing we might learn from settling Mars is what the earth's carrying capacity is.

-- RobS

Bill White · 2002-01-30 19:55:09

Anyone interested in using mirrors and light tubes to greatly increase the sunlight within a dome or other settlement should look at the following website:

www.solartube.com

Mirrors and other collection devices can be spread outside the dome and the light piped in with devices such as those sold by solartube.com.

But, given the reality of dust storms, a 50% reduction in sunlight (due to Mars be further from the sun) and further % reductions depending on the number and transparency of dome fabric layers, I believe a reliable and exceptionally efficient source of artificial light will remain necessary. For that requirement I suggest looking at the following website:

www.sulfurlamp.com/tech.htm

The artificial light, of course, will need a powerful source of energy (especially during dust storms) which points plainly at nuclear reactors - for better or worse.

Shaun Barrett · 2002-07-13 02:42:52

I've been thinking again lately about the problems of building domes on Mars. More specifically, I've been chewing over the problem of pouring concrete and getting it to set properly under Martian conditions.
In this forum and in "We need a brainstorming session ... !", we discussed using pressurised tents in which we could do concreting. But how to anchor such a tent and move it along as the building took shape was causing us problems.
I've come to the conclusion that the only shape of tent that won't require anchoring (except against the wind), is a cylindrical tent. And I propose laying the dome foundations inside a kevlar reinforced transparent plastic cylinder which can be increased in length section by section, by the simple expedient of laser 'welding' a fresh length of cylinder onto the end of the last one.
Let's imagine that we've reached the stage of wanting to build a large dome and that the infrastructure to do this has been developed. I suggest we build a "dome" with a base in the shape of a regular hexagon, 500 metres on a side. The curve of the transparent dome material can be decided separately, but the higher the centre of the dome, the more air-shielding we get against radiation.
Let's assume I'm correct in my earlier premise that the upward pressure on the dome is determined by the air pressure and the ground area enclosed, and only these parameters. And let's assume we want an atmosphere of 500 millibars. Now we can do a little arithmetic.
Without boring you with too much detail, I've calculated the ground area of our hexagon will be 650,000 square metres. 500 millibars of air pressure translates to 5.17 tonnes of upward pressure per square metre of ground enclosed. We therefore have to counteract a total "lift" of 3,360,500 tonnes!
Assuming we want an entirely uncluttered airspace inside the dome, all of this upward force must be opposed by the perimeter foundations alone. The perimeter is 3000 metres long, which means each metre of it has to weigh 1120 tonnes. This is a lot but it's not a fundamental impediment to the plan.
On Earth, we can rely on the average concrete mix to weigh 2.242 tonnes per cubic metre, more of course if it has steel reinforcing in it. I'm going to assume we can get Martian steel-reinforced concrete to weigh 1 tonne per cubic metre, which means that for every metre of perimeter, we'll need at least 1120 cubic metres of concrete (regocrete if you prefer, since we'll be making it out of Martian regolith! ).
Here's where the tranparent cylinders come in! First we dig a half-cylindrical trench with a diameter of 54 metres and a length (arbitrarily) 100 metres long. Next we place our 54- metre-diameter-100-metre-long transparent kevlar-reinforced plastic cylinder with large airlock at each end, into the trench. Inflate the cylinder with standard Martian air (30% oxygen, 70% nitrogen) at 500 millibars, or whatever is most practical. The lower half of the cylinder should be a neat fit in the trench, touching the ground in most places, while the upper half of the cylinder protrudes above ground level. The air in the cylinder will be warmed by the sun during the day but may need artificial heating at night.
Colonists can then assemble a reinforcing framework of steel bars in the lower half of the cylinder, with a continuous rail-like portion of the steel protruding above ground level. Next, the colonists, working in shirtsleeves inside the tube, can mix and pour concrete to gradually fill the lower half of the cylinder until only the steel "rail" remains visible. You now have a half-cylinder of reinforced concrete a hundred metres long, 54 metres across, flush with the ground, and with a steel rail along the centre-line of the cylinder, protruding out of the concrete. A simple calculation reveals that this construction, by serendipitous good fortune, happens to weigh 1145 tonnes for every metre of its length! (I cheated ... I did the sums first!! )
The next stage involves extending the trench and 'welding' another 100 metre tube of plastic onto the end of the first one, with a large airlock at its free end. This tube is then inflated and the airlock between it and the first tube can be cut away from inside. We now have a 200 metre long pressurised environment in which to continue the reinforced concrete foundations.
Eventually, you will have a hexagonal foundation 3000 metres long, weighing 3,435,000 tonnes, flush with the ground, and with a convenient steel rail running along the middle of it, to which the transparent dome can be firmly attached. Once you are satisfied that the concrete is truly set, the half of the transparent cylinder protruding above ground can be sheared off at ground level.
This method of foundation construction allows for a worker-friendly environment and an environment in which concrete can be poured and set with relative ease. In addition, the dome itself will go almost all the way down to ground level, giving the inhabitants that all-important feeling that they are living "out in the open" on the surface of the planet. Most of the posts I've read on this subject seem to agree that psychologically this is extremely important.
People have suggested driving piles into the ground to help secure the foundations. But this assumes the ground will retain its structural cohesion. With terraforming bringing about warming of the regolith, the piles may become less reliable as the permafrost softens. Using massive foundations, as in my plan, relies solely on weight and is therefore not susceptible to changes in the consistency of the ground.
I have assumed we can produce steel out in the open on Mars since the vapour-pressure of molten steel is extremely low. I have also assumed we can manufacture plastics and kevlar by some form of extrusion process without too much trouble. If we can't, we might as well forget the whole thing and stay home!!
Any thoughts?

Byron · 2002-07-13 06:57:51

Wow...all I can say is that you've put in some major "gray matter" processing time into this... .

On first reading, your "proposal" sounds like a grand idea for building a practical, large-scale dome..one that seems to have a very good chance at working...however...(sorry, you know there has to be a "but" or "however" in there somewhere!), my main concern with this is the sheer mass of the concrete that would have to poured into place and allowed to set...100 X 54 meter blocks is a lot of concrete. This huge volume of concrete would literally take years to set, and it would have to be built like the Hoover Dam in the U.S...block by block, so the concrete can set up in pieces. I'm not saying this is an impossible thing to do..only that it will take a very long time. (Meanwhile you have the new settlers huddled in their temp tents, tin cans or whatever, anxiously awaiting the day they can move into their "real" home..lol.)

You mentioned that the use of piles driven into the ground could pose a risk in case of warming by terraforming...but I think only the top 50 meters or so of the regolith will be affected (at least in the first couple of hundred years or so)....the piles would be driven much deeper than that...up to 500 meters in, perhaps? What I would propose is a plan similar to yours, but about one-third to half the volume of concrete to be used, with the remaining weight to be offset by piles made of steel placed into bore holes drilled at a 45-degree angle in towards the center to create a "claw-grabber" effect. Construction time could be reduced and costs would be lowered...as concrete work is a very labor-intensive excercise. (You have to mine the raw materials for producing cement in the first place, you have to mix it all with a great deal of costly water, forms have to be constantly constructed and taken apart for the pouring process..the list of tasks goes on and on for concrete work...lol.)

But that's just my opinion...what do the rest of you think?

B

Shaun Barrett · 2002-07-13 19:39:01

Thanks, Byron, for your response to my plan. You've raised some interesting and very pertinent criticisms. It has, in fact, been percolating through the recesses of my mind that I have conjured up an awful lot of concrete in my proposal!! (My wife has actually on occasions drawn parallels between my mind and concrete ... in terms of density, I think! )
I do in fact prefer your option of sinking foundations deep into the regolith, if that can be shown to be a safe and practical alternative to sheer mass in the foundations. But we don't know enough about Mars to be sure of the structural integrity of the crust at this stage. It might be much like loose gravel from the "gardening" effect of impact events over the eons, and may be unsuitable for the type of anchoring you suggest. And the permafrost layer may be shallow in places if there is more areothermal heat emanating from inside the planet than we think. (This happens to be a pet theory of mine ... that Mars is more volcanically alive than many people surmise.)
I understand your objection that colonists can't be expected to live in 'temp tents' and 'tin cans' while they wait for nearly 7 million cubic metres of concrete to set! The murder and suicide rates would go up for sure!
But the scenario I outlined would be taking place well after the 'tin can' phase of settlement. Much more comfortable quarters would be commonplace by this time. I was referring to the stage when the new Martians are ready to start some major projects .... like the establishment of a small city. A major dome would allow for this from a practical viewpoint, while constituting a demonstration (possibly directed at Earth) that the colony had come of age and could achieve impressive feats of construction. Even if it took 2 or 3 Martian years to complete, it would be worth it for 65 hectares (about 160 acres) of open usable space.
I seem to remember from past posts that at least one of our fellow contributors to New Mars is involved in the construction industry. Perhaps my wife is right about the concrete in my head because I can't recall exactly who that person is! If they are reading this, could they please give us some input on the question of getting large volumes of concrete to set? For instance, how many cubic metres at a time can be poured and how long would we have to wait before pouring the next batch? From this we could work out how long it would take to finish each 100 metre section of my proposed hexagon. By the way, how good is this quick-setting concrete I've heard about?
Thanks again, Byron! It's great to get different points of view on these things. However hard you try to iron out any creases in a hypothesis, you invariably miss a few .... and a fresh angle from somebody else always adds new insights to the problem.
Can anyone else help?

Phobos · 2002-07-14 21:16:03

I seem to remember from past posts that at least one of our fellow contributors to New Mars is involved in the construction industry. Perhaps my wife is right about the concrete in my head because I can't recall exactly who that person is! If they are reading this, could they please give us some input on the question of getting large volumes of concrete to set? For instance, how many cubic metres at a time can be poured and how long would we have to wait before pouring the next batch? From this we could work out how long it would take to finish each 100 metre section of my proposed hexagon. By the way, how good is this quick-setting concrete I've heard about?

Actually concrete will setup fairly quick regardless of how much you pour. 7,000,000 cubic yards of concrete will setup just as quickly as 10 cubic yards of concrete. If you make the slab a reasonable thickness, say two or three meters at most (which is very thick!)), you will have no problem with it curing to full strength in the typical 28 days provided you keep the temperature constant. And you'll have to be careful about pouring the concrete in sections as cold joints will develop and wreck the structural integrity of the foundation. Anyways, your going to need some massive pumps, mixers, and finishing machines for a concrete job of that scale. Mars will definately be on its way to being a civilization in its own right once such a big project can be realistically contemplated.

The only thing I worry about is the concrete that is poured into the massive footings. I'm not sure how well you could regulate the temperature of concrete that is underground on Mars, particularly if you go very deep, which you probably would. I might point out to that not all concrete is equal. There are different mixes of varying strengths for different types of jobs. If you used a very high strength mix, say 6000psi, and properly reinforce it, that thing won't be going nowhere unless it grows legs and wants to.

As for how long it would take to pour all that concrete, the most I've seen a contractor pour in one day was about 5000 cubic meters of concrete. Since those concrete trucks you see on the road with the rotating drums can only haul between 10-15 cubic meters of concrete, that 5k meter job took upwards of about 300-500 truck loads. And that was with five or six pump trucks pumping about ten trucks at a time. So pouring 7 million cubic meters, it's gonna be a bastard!

Byron · 2002-07-15 06:53:41

In response to my previous post concerning the huge volume of concrete in Shaun's "proposal," I've found a snippet about the construction of Hoover Dam, built in the mid 1930's, and at 2,600,000 cubic meters, it has more mass than the mighty Pyramid at Giza, and yet it took less than 5 years to build...an amazing feat for that era...

--Quoted from the U.S. Department of the Interior Website--

"As the dam began to rise to fill the canyon, it grew it fits and starts. Rather than being a single block of concrete, the dam was built as a series of individual columns. Trapezoidal in shape, the columns rose in five foot lifts. The reason that the dam was built in this fashion was to allow the tremendous heat produced by the curing concrete to dissipate. Bureau of Reclamation engineers calculated that if the dam were built in a single continuous pour, the concrete would have gotten so hot that it would have taken 125 years for the concrete to cool to ambient temperatures. The resulting stresses would have caused the dam to crack and crumble away.
It was not enough to place small quantities of concrete in individual columns. Each form also contained cooling coils of 1" thin-walled steel pipe. When the concrete was first poured, river water was circulated through these pipes. Once the concrete had received a first initial cooling, chilled water from a refrigeration plant on the lower cofferdam was circulated through the coils to finish the cooling. As each block was cooled, the pipes of the cooling coils were cut off and pressure grouted at 300 psi by pnuematic grout guns.
To prevent the hairline fissures between the blocks from weakening the dam, the upstream and downstream faces of each block were formed with vertical interlocking grooves; the faces turned toward the canyon walls with horizontal vertical grooves. When the concrete had cooled, grout was forced into these joints, bonding the entire structure into a monolithic whole.

Hoover Dam was the first man-made structure to exceed the masonry mass of the Great Pyramid of Giza. The dam contains enough concrete to pave a strip 16 feet wide and 8 inches thick from San Francisco to New York City. More than 5 million barrels of Portland cement and 4.5 million cu. yds of aggregate went into the dam. If all of the materials used in the dam were loaded onto a single train, as the engine entered the switch yards in Boulder City, the caboose would just be leaving Kansas City, MO. If the heat produced by the curing concrete could have been concentrated in a baking oven, it would have been sufficient to bake 500,000 loaves of bread per day for three years." End quote --

Hope this gives you a better idea of what is involved in massive projects involving the use of concrete...but if a project of this scale could be accomplished in the
1930's, there's no reason to doubt it couldn't be done on Mars in the future...

B

Shaun Barrett · 2002-07-15 22:38:42

Absolutely fascinating reading, Byron!! Those Hoover Dam statistics certainly put my dome foundations in perspective, don't they?!
And Thankyou, Phobos, for those practical observations and interesting facts .... particularly the part about the 5000 cubic metres of concrete being poured in one day.
My initial impression is that the Hoover Dam was probably a significantly more complex construction than my dome foundations, but then we have the added difficulty of having to work in a much more hostile environment (though I've read that 1930s America was a hostile environment in its own way! ). For a start, we don't need to build up. We're simply pouring concrete into a "hole in the ground". In addition, if our steel reinforcing is well constructed, watertight junctions between batches of concrete won't be necessary. All we're doing is creating coherent mass.
Is there any difference between 1930s concrete and the stuff we use today? The reason I ask is that Phobos told of that 5000 cu.m of concrete in a day, but didn't mention anything about huge heat build-up during the setting process. In any event it may not matter to us because if there's one thing we've got plenty of on Mars, its refrigeration!! I'm sure we could come up with a way to utilise heat from the curing concrete to offset the extreme cold of the regolith we're pouring the stuff into. (Plumbing ideas anyone? )
It's encouraging to read that the 2,600,000 cubic metre Hoover Dam took less than 5 years to complete. It may prove possible, in view of its lesser complexity, to complete the nearly 7 million cubic metre dome foundation in a similar time-frame. If the half-cylindrical ditch work, the plastic tube placement, and the steel reinforcing framework are largely completed first, it then becomes possible to start pouring concrete at many different points around the hexagonal perimeter. If two metre deep layers of concrete are poured and then left for a month to set, the work team can move on to another area, and then another. If many teams are carefully "choreographed" to work to a plan, good progress could be made. I realise this would require duplication of expensive equipment, but in principle it should work. If time is not the most important factor, then by all means minimise your equipment and do things at a slower pace.
It may be advisable in the earlier years of colonisation to "cut your teeth" on smaller projects to test the principles of dome construction. I've recalculated the figures for a hexagonal "dome" only 50 metres on a side. A dome this size will only enclose an area of 6500 square metres (just over 1.5 acres) but needs only 5675 tonnes of reinforced concrete per side of the hexagon. i.e 34,050 tonnes of foundations in total. A much more manageable thing all together! But then your dome height won't be any more than 100 metres, which means not much air shielding against radiation.
Anyway, what I've tried to show is that major concrete construction in a near-vacuum on Mars is at least feasible. Most of us seem to prefer the idea of living under a dome rather than under the ground. Bigger domes mean more air shielding which means safer "outdoor" shirt-sleeve living, which to me is the next best thing to living on a fully terraformed Mars. If some form of construction is desirable and enough people want it, I have great faith that a human engineer will find a way to provide it ... regardless of the difficulties involved!!

Phobos · 2002-07-18 20:30:42

Yeah, you have to be careful that concrete doesn't get to hot, but generally that shouldn't be a problem with a foundation since it's thickness won't really be anything on the
scale of the Hoover Dam.

I wonder about the equipment that will be used. I'm thinking the project could be finished extremely fast once you mine all
the material for the concrete. Since it's very likely you won't actually have to drive the wet concrete around, you could set up very massive stationary mixers with pumps and hoses
attached to booms that would deliver the concrete right to where you want it. Once one section is done, the empty mixers could probably be towed to another portion of the slab, the hoses and pumps laid out, and the construction restarted. If you had multiple shifts working around the clock
to pour the slab and assuming your big mixers could get you 30,000 cubic meters of concrete daily (which I don't think will be a problem since you wont have to transport it wet like we do on Earth) you could pour your 7 million cubic meters in under a year provided your very efficient.

Shaun Barrett · 2002-07-19 18:45:32

If it's found that large domes are really the best way to colonise Mars, a colony would probably devote a great deal of time and resources to their construction.
Once the large concreting machines are available, and efficient large-scale mining of the regolith for materials is established, it may become common for enormous domes to be erected in surprisingly short time-frames. As Phobos points out, a 1 kilometre diameter dome might be finished in less than one Earth year!
Imagine the progress we could make!

Phobos · 2002-07-19 20:14:45

I think domes are the best way of making Mars colonizable on a big scale short of terraforming. It would be nice having all of that running room and not having to wear a spacesuit. In addition to pouring the foundation though, I imagine you would want to have all of the structures you plan to build on top of the foundation already designed before you pour so items like underground electrical and plumbing conduits would match up nicely with the buildings. I don't think you'd want a bunch of electrical lines just hanging in the air or laying on top of the concrete foundation. It would probably be best to bury them in the concrete itself.

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