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So, we've reached The Moon/Mars. Our band of intrepid Colonists/Lunatics will almost certainly start by working out of prefabricated facilities (ship, habitat etc) but they will eventually run out of space.

Trivially they will want enclosed space for fields of potatoes, industrial facilities or a few spare rooms so they can have 10 minutes of private peace and quiet. Thing is, how do you build such a room?

The issue is keeping it airtight. Ignoring the issues of an airlock, the simple problem of making a room seems incredibly hard. A metal room would require the full purification of iron or metal alloys that can be welded (?) into something that doesn't leak like a sieve.

Our fiction is full of geodesic domes, transparent glass and other incredible complex structures. I'm having problems imagining the construction of a simple box room on the surface. Let alone pipe in air, power and water, and pump out air and waste water. Or an airlock built in situ.

So - how do we do this?

Edit: Additional constraints, based on comments.

  • Near future tech. Assume anything we can make or nearly make now.
  • Local resources where possible.
  • Local labour, 2-3 people with some mechanical assistance
  • Limited production space. You've got the ship they came in, a few dozen cubic meters of space. You don't have a large airtight hanger you can build smaller things in and wheel out into position

Hard science appreciated but not tagged. Happy to take soft suggestions.

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  • $\begingroup$ Are you talking about construction using ONLY locally acquired raw materials here? $\endgroup$ – Morris The Cat Aug 13 at 16:31
  • $\begingroup$ You might as well ask "how do we build a building noawadays"? There is just too many steps involved. This wouldn't be answerable with anything shorter than a whole engineering encyclopedia. $\endgroup$ – Renan Aug 13 at 16:31
  • $\begingroup$ Local materials, yes. "How do we build nowadays" is a much easier question. The sticky bit is strictly the airtight bit. It's simply not a constraint we have on Earth. $\endgroup$ – user2702772 Aug 13 at 16:33
  • $\begingroup$ Submariners would strongly disagree that we don't have the constraint of building controlled airtight structures here on earth... But your question seems overly broad and unfocused, and is probably best broken down into more manageable chunks or scaled back to more specific 'starting conditions'. [At least something like 'if we've established X, what would Y look like' gives a little more to go on.] $\endgroup$ – TheLuckless Aug 13 at 16:49
  • $\begingroup$ Submarines are still built on the surface, in an environment where we have air to work with. Similar question would be "How could we build a sub under water?" $\endgroup$ – user2702772 Aug 13 at 17:01
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Laser Syntered Regolith

First the dust and rock on the surface of the Moon would need to be passed through sieves, to enable the grade of material suitable for printing to be fed to the printer head.

The process itself would be very much done as a 3D printer does it now, but being heated by lasers instead of a small scale heater element:

building up products layer by layer in a semi-molten state until they set into stabilize in solid form.

This produces a porous but mechanically stable material in any shape that you can conceive of. The final step of making it airtight would be achieved by increasing the temperature in a process known as Selective laser melting.

There are companies - Regolight being one, among probably several which are developing 3D printing techniques for the express purpose of building habitats on the Moon/Mars. (No affiliation to the author of this answer).

Although presumably someone could go to the trouble of building separate life support systems for each cabin section, perhaps a centralised oxygen production facility would be more appropriate, both from water found on the Moon, and by the plants in the horticultural/hydroponics areas. A system like a Central ducted air system, could be used to distribute fresh air and control temperature. This would be in a fern like structure branching out from the central areas to living quarters. This has the advantage that it can grow outward indefinitely as demand dictates. A "stale air" return ducting system would be build along-side it.

Emergency respiration systems/spacesuits would always be available, with emergency bulkheads to close in case of a breach and perhaps hatches on the roof of every room to allow rescue.

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  • $\begingroup$ I was going to go slightly simpler, lower weight and lower tech, Solar rather than Laser, but this was pretty much my answer too. $\endgroup$ – Ash Aug 13 at 17:20
  • $\begingroup$ @Ash Maybe your way is the one to go until the colony's established and has "unlimited" power to play with lasers big enough for the job. $\endgroup$ – 011358 smell Aug 13 at 17:22
  • $\begingroup$ Can this solution be set up completely on the surface or do you need internal spaces to work from? If the latter my answer may still be worthwhile. $\endgroup$ – Ash Aug 13 at 17:24
  • $\begingroup$ @Ash Genuinely not sure at the moment, it's still in the development phase. It strikes me that large structures would cool down slower in near vacuum and so contain fewer internal stresses liable to form faults. I'd like to hear your answer. $\endgroup$ – 011358 smell Aug 13 at 17:28
  • $\begingroup$ Power wise, solar wins. A few lenses are cheap, weight wise... and this example from Earth looks reasonable. dezeen.com/2011/06/28/the-solar-sinter-by-markus-kayser Only 40% of the solar energy, so bigger lenses, but doable. And can entirely be done on the surface. Possibly remotely even. $\endgroup$ – user2702772 Aug 13 at 17:29
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Providing a comprehensive answer to "how do you build a base on mars" is a bit beyond the scope of a simple answer here, so I'll focus on the core of your question: what can you use to make an airtight chamber on mars?

Turns out that bit, at least, is pretty easy: marscrete! You need to obtain sulphur (which mars seems to have reasonable amounts of), heat it up to its melting point (a mere 388K), stir in a generous quantity of regolith, chuck into a mould (or conceivably spray onto a surface) and allow to cool. You could probably 3d print things with it if you liked. A thick enough layer of a decent concrete can certainly be airtight, so you can construct external buildings or line excavations as you like.

(Also, don't assuming that getting metal is going to be that difficult. The problem has already been considered and there are various options available.)

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  • $\begingroup$ Looks good for later development, but isn't room one. Maybe room 5 though, $\endgroup$ – user2702772 Aug 14 at 5:30
  • $\begingroup$ @user2702772 uh, what does that even mean? I can't quite see how sulphur concrete is less reasonable than laser sintered concrete... if nothing else, it already exists in the real world. $\endgroup$ – Starfish Prime Aug 14 at 6:31
  • $\begingroup$ So, laser/solar sintering, both of which have been proved in principle on Earth, would allow a crew to roll out of the ship and start building it on day 1. Sulphur concrete will require the extraction of sulphur, melting, combining with regolith and then deploying. Fairly straightforwards, but it would be a longer and more complex operation than just "point the solar death ray at the regolith". Your approach has merit, and would almost certainly be deployed - but I can't see it being The First Room built. $\endgroup$ – user2702772 Aug 14 at 14:31
  • $\begingroup$ @user2702772 the research paper I linked was written with the intent of doing exactly that. Remember that extraction and refinement of raw materials can be done in advance of any human presence. Your solar death ray is limited by weather and time of day, and the speed at which it can be operated, can't trivially be used to line underground structures and has limitations when used with some kinds of reinforcing or pretensioning, etc etc. Not that I'm particularly interested in defending the paper here (or attacking the alternatives), but, y'know, things to bear in mind. $\endgroup$ – Starfish Prime Aug 14 at 14:36
  • $\begingroup$ You're missing the volume problem. Using concrete requires you to mix batches; for a 3mx3mx3m room with 5cm walls, that's about 2.7m3 of concrete that needs to be mixed and layed ASAP. If you're going it in multiple loads you have a seal issue at the borders between pourings. This is fine, when you have the work space to produce a large batch. But harder on day one. $\endgroup$ – user2702772 Aug 15 at 7:29
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The rooms are built in vacuum, and then filled with atmosphere, after a leak test.

The mechanical engineering of keeping vacuum and atmosphere separate is well developed today. Many of our manufacturing processes require high vacuum conditions to ultra-high vacuum conditions similar to the moon.

Assuming your building materials are being fabricated on the moon, you would want them to be corrosive resistant -- not from a vacuum but from the human space inside. Pure iron would rust because of atmospheric water. Better to go with forms of stainless steel that are strong and flexible and resist corrosion. In a vacuum, they can be easily welded to make gas-tight joints. Wall Penetrations used to route piping and electrical power and signals might be shipped up from the earth in early days since they are typically precision ceramic stainless steel constructs that are too difficult to reliably fabricate on the moon until the larger industry is developed. These fittings are welded into holes machined in the wall and provide very durable and reliably interconnects.

Some joints might use CF gaskets. These are useful connecting lengths of pipe together.

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For extra safety, I would imagine the insides of the habitats would be coated with a goo that would harden when exposed to vacuum. This would prevent minor leaks from becoming dangerous by flowing into cracks and punctures, and then sealing the damage.

Similar ideas could be used to seal the ground beneath habitats so some of the walls of the structure could be excavated and sealed moon stone.

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Here are a few ways that could be used:

  1. Some kind of automated refinery robot is sent beforehand, to extract useful stuff and process it into all kinds of things, for example water and rocket fuel. Once this is done, you can start to manufacture all kinds of building materials from the collected stuff. Water, by itself or as pykrete could even be used as such, since we are talking about very cold places. Existing proposals typically extend a preformed inflatable "bubble" out of one end of a landed cylinder (the other end has the airlock), and then use local material to reinforce it. Pure water ice could even let some light in through the ceiling, without compromising on radiation/micrometeorite protection.

  2. Loose dirt is processed somehow so that it hardens into molded shapes, like concrete. Lunar dust has not been abraded by erosion, which means that it naturally has jagged edges, like the kind of sand preferred in construction on Earth. Based on one trial of microwave sintering an actual sample of moondust brought back by the Apollo program, a "lunar lawnmower" has even been proposed, which would run over the ground and harden the dust in place into lunarcrete. Without some further trials, it is hard to say if this method would actually scale.

  3. Use local geological formations as part of buildings. For example, natural caves or mine shafts could be appropriated as walls and floors, requiring less structure to be built from scratch. This option is also dependent on surveying the local conditions: without a thorough understanding of the existing natural walls, you could end up with unsafe structure, or a habitat with harmful substances slowly seeping in from the ground (e.g. Radon gas).

Everything that is not built around an inflatable bubble needs some insulation and sealing layers, applied on the inside and possibly outside as well, before first pressurization. A large cave might need to be "washed" with a gas mixture multiple times, to find leaks and structural problems, and also to filter out the loose dust remaining indoors.

Airlocks could be a problem; making an advanced spaceship component from scratch locally is not a simple matter. Imported airlocks could also have their seals wear quickly from the ever-present jagged dust. One creative proposal I have seen that could avoid these problems is the "liquid airlock", but because of the height requirement (60 m for water) it looks mainly suitable for a large cave-type habitat.

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