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It has been suggested that lava tubes at Hadriacus Mons could provide a location for a human habitat that would screen out harmful radiation.

https://en.wikipedia.org/wiki/Hadriacus_Mons

My idea for a colony is that it was initially built inside the lava tube (which I gather is huge - 190m wide, 160m tall (100m below surface). This could hold say a 50-story structure of some kind. Once in place, you could extend structures through the surface with radiation protection so you could have windows and a view outside.

Space isn't a problem, but I'm thinking materials are. Assume this is in the future and we have advanced ships and a presence on Mars for many decades - beyond exploration and into settling.

Question: What's the best method to build a city colony structure in the lava tube?

Would it make the most sense to build a "skyscraper" inside with access to the surface? Or would there be some better way to build in this huge open space? Alternately you could begin tunneling in to the rock itself within the tube and build inside the Mars rock itself.

Apparently you might be able to make "mooncrete" (https://en.wikipedia.org/wiki/Lunarcrete) - could you make a sort of "marscrete?"

NOTE: Think long term, big city, permanent settlement - we are past the exploration stage.

EDIT: People are still thinking of the exploration/astronaut stage -- think more about this as a full fledged functioning colony 100 years later. As I said in my note - big city. We are beyond worrying about potatoes for food and oxygen. We have the technology to reliably put oxygen safely in the whole structure. We can ship food and materials in from Earth or other colonies. That's the background. Now we want the best structure with that in mind inside the lava tube.

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  • $\begingroup$ Ok, I took out some extraneous info and simplified my ask. Mainly want to understand building a structure in the tube vs. digging into Mars itself. $\endgroup$
    – MajorTom
    Apr 8, 2022 at 19:48
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    $\begingroup$ Looks good, I'm not certain what H. Mons is made of, or even if we know. Could be you might need to take an answer and use what fits best your story if there are no definitive answers regarding the ease of digging etc.. $\endgroup$
    – Escaped dental patient.
    Apr 8, 2022 at 19:54
  • $\begingroup$ +1 intriguing idea.. In the Wiki-topic there are two references.. for the record I paste them, Letzter, Rafi (2020-05-11). "These lava tubes could be the safest place for explorers to live on Mars". livescience.com. Retrieved 2020-05-11. Paris, Antonio; Davies, Evan; Tognetti, Laurence; Zahniser, Carly (2020-04-27). "Prospective Lava Tubes at Hellas Planitia". Journal of the Washington Academy of Sciences. arXiv:2004.13156. $\endgroup$
    – Goodies
    Apr 8, 2022 at 22:21
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    $\begingroup$ @MajorTom In response to your edit, it is unclear what worldbuilding problem you are trying to solve. Or what problem the colonists are trying to solve. I say "here is an efficient way to build the city" you say "we are advanced enough, we don't need to worry about efficiency". In that case what do you mean by "best" way to build it? $\endgroup$
    – Daron
    Apr 9, 2022 at 20:11
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    $\begingroup$ @MajorTom more like a few city blocks, depending on usable length. And why use it? It's hundreds of meters underground, it's location was determined by ancient volcanism, not the locations of transport infrastructure, mineral resources, or other useful land surface, and preparing for habitation and any future expansion will require burrowing through the surrounding rock which may or may not be well suited for tunneling. You don't have to excavate a surface city either, just cover it with regolith for shielding, and you can do that anywhere on the planet. $\endgroup$
    – Christopher James Huff
    Apr 10, 2022 at 17:38

6 Answers 6

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3D printing….

Building on the experience learned from building moon habitats that used 3D printing a lot has been learned that can be transferred to Mars. Of course neither the moon or mars have a lot of free water, so 3D printing of concrete like materials was more difficult than on Earth. On the moon the scaling up of solar sintering turned out to be important. On Mars since less sunlight was available, fusion furnaces were used to sinter the crushed and processed mars rock instead but many of the control systems and robotics and software to plan out the city were based on what was learned on the moon.

Edit: Here is is a link showing some 3D printed concrete structures presently being done (on earth). 3D concrete printing These types of techniques could be automated and used to smooth out the lava tubes, help provide more smooth sealable air tight surfaces, as well as build structures in the tubes.

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  • $\begingroup$ Are these 3D printed moon habitats real or imaginary? $\endgroup$
    – Daron
    Apr 9, 2022 at 13:13
  • $\begingroup$ Water won't be a problem in this imagined future. Maybe we're just shipping in massive ice blocks from somewhere else in the galaxy via huge cruiser ships. This is the future and interstellar travel is not a problem. $\endgroup$
    – MajorTom
    Apr 9, 2022 at 14:12
  • $\begingroup$ @Daron The moon habitats are imagined, but NASA and others are seriously considering using 3D printing one possible route. Presently, on earth 3D printing of concrete really is a thing. all3dp.com/1/3d-concrete-printing-guide and may be especially useful for some types of low cost housing. $\endgroup$
    – UVphoton
    Apr 9, 2022 at 14:25
  • $\begingroup$ @MajorTom if water is available, then it is a lot easier! $\endgroup$
    – UVphoton
    Apr 9, 2022 at 14:33
  • $\begingroup$ @UVphoton Hmm. . . It looks like it would be low cost in the sense that you need to hire fewer humans to work on the building site. But you still need someone to put the girders into the concrete. $\endgroup$
    – Daron
    Apr 9, 2022 at 15:15
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Start building in the middle of the tube. That means you can transport materials from both directions rather than just one. Build the heavy structures here in the middle. Like nuclear reactors and water purifiers and oxygen makers.

Build the potato farms on either side of the tube. They need sunlight after all. People also require sunlight to not go bonkers insane. So build homes on either end of the tube near the farms. (Edit: That means the yummy potato oxygen can be pumped into the homes) Make sure to leave a long throughfare between the two sides of the tube. You will need to expand the homes deeper into the tube as population increases.

Don't burrow into the tube wall. There is no need for this. The tube is already burrowed into the mountainside. Why burrow further. It needs the same amount of materials, since you still need to build walls inside the walls to run electrical wires and heating tubes behind.

A single large building is a bad idea. You want each home to have a separate oxygen supply. That means even if one home starts to leak space air you can just run next door.

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Gonflable!

inflatable house

AKA inflatable building. You need to blow pressurized atmosphere anyway because we like that. Let the atmosphere you blow in there serve a structural role too. Down in the tube all you need is to keep the atmosphere from blowing away and a strong inflatable shell will do fine. It is cheap. It will conform to the tube walls. It is easy to make it modular for expansion or rearrangements. It is easy to patch from the inside.

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  • $\begingroup$ I don't think this would work for a city. Maybe I wasn't clear enough on that (I will adjust question). Maybe early days you do something like this. But for a permanent, long term settlement not sure this works. Also, the tube walls are huge - like I said you could fit a building in there. $\endgroup$
    – MajorTom
    Apr 8, 2022 at 21:04
  • $\begingroup$ @MajorTom - you are going to need balloons or something like them anyway to retain atmosphere. Maybe the balloon is all you need. If you are worried people will wear out the balloon material with their dirty boots you could have rugs. $\endgroup$
    – Willk
    Apr 8, 2022 at 21:31
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My idea is a rotating donut-shaped base living area that would constantly be spinning to passively give astronauts their share of exercise while working. The donut would be on thick steel poles that extend to the sky about 10m. The donut will also be made out of steel.

Although Mars dust can be a big problem for it can be detrimental to the lungs and is electrostatic, in order to enter, their will be a series of airlocks. The first is where they will 'dock' their spacesuit after work outside, which will most likely be covered in dust. After docking, they will slide out into a room, and then go into the main hub.

Food will be a problem to, so an area for aquaponics would be set up to provide astronauts with a nutritious variety of foods.

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  • $\begingroup$ Why does the donut spin? $\endgroup$
    – Daron
    Apr 9, 2022 at 13:14
  • $\begingroup$ The donut spins to passively help the astronauts exercise. $\endgroup$
    – TempzApex
    Apr 10, 2022 at 5:45
  • $\begingroup$ How does spinning help with exercise? $\endgroup$
    – Daron
    Apr 10, 2022 at 12:13
  • $\begingroup$ @Daron presumably, the purpose of the spinning donut is to provide gravity close to Earth normal. The inside surface would be a section of a cone, so that centrifugal force and Mars's gravity combine to produce 1g of force for someone standing on the surface. Whether this is needed or not depends on the long-term physiological effects of living in reduced (but not zero) gravity, which are currently unknown. $\endgroup$
    – N. Virgo
    Apr 11, 2022 at 2:31
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I assume that since you want to build a city the first phase of the colonisation is already advanced. Thousand of small living modules sent from Earth where used as bases to build many glasshouses to grow food, now Mars is dotted by many villages. Those villages used Martian perchlorates as a source of oxygen and energy, but now to build a city they need a lot more energy, from Earth they'll send a mini nuclear reactor. It will be used to process Mars ores and build some more.

Once you have abundant energy you have a lot of different choices. Since aluminium and magnesium are abundant on Mars surface, the easiest way is to use them in alloy to make prefabricated building parts. It will be easy to transport them to the building site thanks to the low gravity. So the prefab parts will be big chunks.

The building inside will have thick layer of a silicone type that is denser than the one used now. Over it instead of plaster there will be a layer of tiles. On the outside they are not necessary until they will have enough resources to seal the tubes and change the atmosphere inside. Bare metal will rot very slowly in Mars atmosphere.

The city will be a single huge lattice structure, with sealed pipes used for walkways, service tunnels and shuttle tracks.

BTW The prefabricated parts will be bolted not welded together. Building a city with a scarce workforce in a difficult environment is expensive. If a marsquake cracked the tunnel, creating the risk of a landslide and forcing people to abandon the area, rebuilding everything from scratch would be difficult. A city on Mars must be a structure that could be dismantled and reassembled somewhere else.

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This concept is covered in the Mars Trilogy by Kim Stanley Robinson. In the novel, the lava tubes are sealed off in 1km sections, pumped up to a breathable atmosphere and 'terraformed' with soil (very hard to make) and water. As you correctly surmise, this produces a very large amount of living space (the lava tubes are 100's of km long) which is shielded from cosmic rays and (not incidentally) well hidden.

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  • $\begingroup$ A bit risky. A quake or an eruption and the place can become a trap. $\endgroup$
    – FluidCode
    Apr 10, 2022 at 20:16

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