Optimal size for domes and other structures

[Pthigrivi]

Okay so playing the game properly I think I’ve come up with a number. This is based on the assumption that we are established on Mars and have the basic capacity to produce: water, oxygen, methane, concrete, aluminum, steel, titanium, and small amounts of plastics. Let's call it 50 years from now. Even with these capabilities we're still largely reliant on earth for pre-fab habitation modules simply because the manufacturing base for everything from chipsets to motors, fittings, precision seals, etc just isn't available without millions of people. This is a concept for a Martian city block capable of housing thousands of people. Because many people will be exposed to radiation while at work we're going to mitigate their exposure as much as possible while at home. Basically the plan is to stripmine the surface to a depth of 6m, process the regolith into anything useful, and then dump the rest on top of the hab modules. That means most of what you see in these sketches is underground and serviced by the kind of artificial skylights shown further up the thread. The only thing above ground are the domed parks. These are built around a central elevator shaft with 12 pizza slices around it which are sized to fit 2 at a time in a Starship Block 3 payload bay. The dome itself is 30m in diameter, and there’s a dome for about every 500 people. I think we can imagine once assembled you have a relatively shielded (about the exposure you have on an airplane) park space with plants, views of the horizon (but not much more) and diffused reflected natural light coming from louvered skylights in the ceiling. These are communal spaces for picnics, small concerts, and family gatherings.  

One of the surprise considerations as I did the math on transit, public, semi-public, family, and personal space was the consideration of fire-egress. This is a very real thing on earth and HUGE consideration on a planet where you can't simply run outside. Every module is designed with a basic 3m airlock so sections can be sealed off from one another and every space has at least two directions of egress, including stairways capable of bringing people to emergency airlocks on the surface if need be. WIP as follows:

Edited Friday at 02:10 AM by Pthigrivi

[darthgently]

1 hour ago, Pthigrivi said:

simply because the manufacturing base for everything from chipsets to motors, fittings, precision seals, etc just isn't available without millions of people.

[Pthigrivi]

14 minutes ago, darthgently said:

Oh for sure, but I think folks underestimate the unfathomable complexity of the modern economy. Just try to imagine the labor and coordination necessary to design, produce, process, manufacture, test, market and transport a refrigerator, a computer, or the ingredients of a decent meal on earth, let alone from toxic frozen regolith. Ive seen some pretty compelling arguments that the minimum self sustaining population at modern quality of life is 300 million. Even with AI and robots you’re going to need tens of millions of people.

Edited Friday at 03:27 AM by Pthigrivi

[tater]

There's also 3D printing as a possibility, possibly buried as well (same concept you propose with stripping away to some depth, then burying with the tailing left over after useful stuff extracted).

I'd like to see concepts that are a more modern take on this building in Milano:

Obviously this has glass on top, but you could have piped in direct sunlight via heliostats, with the glass being opaque so it seems like bright sunlight through thin clouds. I'd probably have loads of greenery as well.

[farmerben]

If you can dig into solid rock, it should be possible to seal the air in with a very thin layer of vinyl which you can mix and spray on with very simple equipment, similar to the way they build fiberglass boats.  This will work even on jagged and fissured surfaces left by tunneling with dynamite.    You can bolt your nice outer wall to the jagged rock and then fill the gaps with epoxy and fiberglass.  

Edited Friday at 04:30 PM by farmerben

[tater]

41 minutes ago, farmerben said:

If you can dig into solid rock, it should be possible to seal the air in with a very thin layer of vinyl which you can mix and spray on with very simple equipment, similar to the way they build fiberglass boats.  This will work even on jagged and fissured surfaces left by tunneling with dynamite.    You can bolt your nice outer wall to the jagged rock and then fill the gaps with epoxy and fiberglass.  

I was involved with a civil engineering in space conference a long time ago, and for a few years there were papers by some of the Los Alamos guys for their "Subselene" nuclear tunneler. Imagine something akin to Boring company (might as well think about THAT as an option as well), but instead of the usual drilling, the front of the machine is heated to the point it melts the regolith it is moving through, minimizing tunnel "mucking" (crushed rock removal) by having the resultant melted regolith seep into the tunnel walls, leaving them glassed. Liners would then be added in case of any gaps.

[darthgently]

32 minutes ago, tater said:

I was involved with a civil engineering in space conference a long time ago, and for a few years there were papers by some of the Los Alamos guys for their "Subselene" nuclear tunneler. Imagine something akin to Boring company (might as well think about THAT as an option as well), but instead of the usual drilling, the front of the machine is heated to the point it melts the regolith it is moving through, minimizing tunnel "mucking" (crushed rock removal) by having the resultant melted regolith seep into the tunnel walls, leaving them glassed. Liners would then be added in case of any gaps.

The trick would be what materials are the business end made of to withstand those temps without becoming one with the resultant glass.  Maybe some kind of gas pressure gap that holds hell at bay until it cools enough or similar

[tater]

5 hours ago, darthgently said:

The trick would be what materials are the business end made of to withstand those temps without becoming one with the resultant glass.  Maybe some kind of gas pressure gap that holds hell at bay until it cools enough or similar

The LANL guys actually built one and tested it at one of the tech areas. They filled a small structure with regolith simulant, and bored into it. Dunno if I have images, maybe the web does.

Not the subselene but could be some of the same guys, actually, and certainly informed the idea (this is a LANL image below, but for terrestrial applications, early 1970s):

https://articles.adsabs.harvard.edu/pdf/1985lbsa.conf..465R

They show the possibility of using smaller penetrators with overlapping edges to make a structure that would then have to be mucked out as well.

This was literally worked on for a few decades (the PDF linked above has the image I remember—but it used the smaller penetrator concept).

Edited Friday at 11:09 PM by tater

[darthgently]

3 hours ago, tater said:

The LANL guys actually built one and tested it at one of the tech areas. They filled a small structure with regolith simulant, and bored into it. Dunno if I have images, maybe the web does.

Not the subselene but could be some of the same guys, actually, and certainly informed the idea:

https://articles.adsabs.harvard.edu/pdf/1985lbsa.conf..465R

They show the possibility of using smaller penetrators with overlapping edges to make a structure that would then have to be mucked out as well.

This was literally worked on for a few decades (the PDF linked above has the image I remember—but it used the smaller penetrator concept).

This is very cool.  Thanks for putting this up.

 It is fundamentally an artificial lava tube.  The building of the arch from the arc of adjacent parallel melts makes for a very large range of sizes that could be fabricated 

Edited Friday at 11:19 PM by darthgently

[AckSed]

6 hours ago, darthgently said:

The trick would be what materials are the business end made of to withstand those temps without becoming one with the resultant glass.  Maybe some kind of gas pressure gap that holds hell at bay until it cools enough or similar.

Found the paper: https://digital.library.unt.edu/ark:/67531/metadc1070838/

[magnemoe]

19 hours ago, tater said:

There's also 3D printing as a possibility, possibly buried as well (same concept you propose with stripping away to some depth, then burying with the tailing left over after useful stuff extracted).

I'd like to see concepts that are a more modern take on this building in Milano:

Obviously this has glass on top, but you could have piped in direct sunlight via heliostats, with the glass being opaque so it seems like bright sunlight through thin clouds. I'd probably have loads of greenery as well.

My university in Norway had something like this less fancy but more advanced I say as it was closed,  it was an group of office blocks, they build in the area between them. Now they had an nice common area and the heating bill went down quite a bit too. Strip malls has some issues over regular malls in Norway during winter. 

Also some places glass over back yards in city blocks.

[Pthigrivi]

42 minutes ago, magnemoe said:

My university in Norway had something like this less fancy but more advanced I say as it was closed,  it was an group of office blocks, they build in the area between them. Now they had an nice common area and the heating bill went down quite a bit too. Strip malls has some issues over regular malls in Norway during winter. 

Also some places glass over back yards in city blocks.

I guess my feeling as an architect is that I can accomplish that exact sensation using artificial skylights manufactured and delivered from Earth much, much more efficiently than I could given in-situ constraints. What is it that’s unique about having visual access to the real environment? It’s a sense of being placed in a geography, its having perceptual access to real light, which is going to be very different on the moon or mars and honestly probably displeasing. Mars gets 43% of the daylight we experience. Light on the moon will be alternately blinding and utterly absent due to the lack of atmospheric diffusion. To feel normal you’re going to need to augment that artificially anyway. I think having real access is still important because it grounds you in a new environment but its not something you need all day. Views of the surrounding landscape for those that don’t work outside will be culturally important but not actually that helpful to our in-born need for earth-like light and vegetation. 
 

Im thinking of doing another test assuming we’re more like 100 years in the future and can produce most anything on the surface. 

Edited yesterday at 01:14 AM by Pthigrivi

[tater]

38 minutes ago, Pthigrivi said:

I guess my feeling as an architect is that I can accomplish that exact sensation using artificial skylights manufactured and delivered from Earth much, much more efficiently than I could given in-situ constraints.

I'm not certain this is correct. You have to remember that 43.7% of the insolation also means more PVs required to capture any desired amount of energy. So for every X square meters of artificial skylight, how many meters of PVs do you also need? My guess is that it is probably close to a PV outside for the same area of panel inside (assuming panels are fixed, not on heliostats). Assuming glass mfg is available early that mass doesn't need to come from Earth, then the math is if heliostats and diffusers can do the job at a lower mass cost than PVs and panel LEDs. I have zero gut intuition about which comes out ahead mass wise—assuming efficiency is mass/cost efficiency. That said, construction with the panel lights has to be far, far easier.

 

35 minutes ago, Pthigrivi said:

Views of the surrounding landscape for those that don’t work outside will be culturally important but not actually that helpful to our in-born need for earth-like light and vegetation. 
 

Very much this. I think seeing outside—and not just dirt, as Mars will tend to lack foreground interest short of interesting rock outcrops. Some long distance view I think is important. Of course I have long distance views of the mountain behind me, and far farther to the west, so maybe I have a warped requirement for sightlines.

[darthgently]

With the seasonal dust storms and the very high power requirements for life support and manufacturing ISRU, base expansion, compute, lighting, screens, etc. I think nuclear power will be an obvious necessity.

If PVs and batteries can eventually be manufactured locally then solar could augment but being that far from the sun and the increased energy demands of harboring terrestrial life on an unforgiving world I don’t see any way around nuclear.  Maybe geothermal eventually, especially if a huge attempt is made to tap that water 20km below the surface.  Might a well tap the heat also, right?

[Pthigrivi]

2 hours ago, tater said:

I'm not certain this is correct. You have to remember that 43.7% of the insolation also means more PVs required to capture any desired amount of energy. So for every X square meters of artificial skylight, how many meters of PVs do you also need? My guess is that it is probably close to a PV outside for the same area of panel inside (assuming panels are fixed, not on heliostats). Assuming glass mfg is available early that mass doesn't need to come from Earth, then the math is if heliostats and diffusers can do the job at a lower mass cost than PVs and panel LEDs. I have zero gut intuition about which comes out ahead mass wise—assuming efficiency is mass/cost efficiency. That said, construction with the panel lights has to be far, far easier.

I was tempted to wave this off suggesting modular nuke reactors or on the the basis of PV install simplicity but Ive been brewing on a simple GCR filter skylight geometry taking advantage of reflected light… slightly curved Vs and As… maybe even precast with reflective mylar coatings? They’d be structural and would have a decent span, especially under reduced gravity. Maybe precast and pretensioned? Its reminding me of Louis Kahn’s Kimble Art Museum in Houston. 
 

14 minutes ago, darthgently said:

With the seasonal dust storms and the very high power requirements for life support and manufacturing ISRU, base expansion, compute, lighting, screens, etc. I think nuclear power will be an obvious necessity.

If PVs and batteries can eventually be manufactured locally then solar could augment but being that far from the sun and the increased energy demands of harboring terrestrial life on an unforgiving world I don’t see any way around nuclear.  Maybe geothermal eventually, especially if a huge attempt is made to tap that water 20km below the surface.  Might a well tap the heat also, right?

Ninjad. The energy density of nuclear fuel is so attractive. Im sure its part of the mix. I feel like Mars and the moon are too geologically dead to provide geothermal? Unless you just mean thermal batteries? The latter is a great idea on the Moon where the day/night temperature cycle is so extreme. 

Edited yesterday at 04:29 AM by Pthigrivi

[tater]

49 minutes ago, darthgently said:

With the seasonal dust storms and the very high power requirements for life support and manufacturing ISRU, base expansion, compute, lighting, screens, etc. I think nuclear power will be an obvious necessity.

If PVs and batteries can eventually be manufactured locally then solar could augment but being that far from the sun and the increased energy demands of harboring terrestrial life on an unforgiving world I don’t see any way around nuclear.  Maybe geothermal eventually, especially if a huge attempt is made to tap that water 20km below the surface.  Might a well tap the heat also, right?

Yeah, I actually agree, but all the talk seems to be PVs because they are less controlled than nukes. I spent a lot of time with the space nuclear power people, though, and it make lots of sense. Put a reactor in a smallish crater, run power to facilities. With sufficient nuclear, then yeah, power is not a problem—though scaling nuclear for space applications is nontrivial given the mostly radiative cooling they're forced into.

[darthgently]

It occurs to me that if there is to be a substantial Optimus bot workforce that will be a big electrical load on its own

Does Mars have accessible fission material?  Launching reactors with no fuel could be a lot less regulated

Grok says “nope” to ISRU of Martian fissionables:

Spoiler

Mars does not have known significant deposits of fissionable materials like uranium or thorium that could be easily harvested for energy production. Here's a breakdown based on available information:

- **Fissionable Materials on Mars**: There is no direct evidence from the web results suggesting that Mars has substantial amounts of uranium or thorium readily accessible for energy production. While Mars has been explored by various missions, none have confirmed the presence of these materials in quantities that would make mining them viable for energy purposes.

- **Challenges and Alternatives**:
  - **Extraction and Refinement**: Even if such materials were present, the process of extracting and refining them on Mars would be extremely challenging, as noted in the discussion on "Generating Energy on Mars: ISRU Part 3". The energy and technological requirements for processing these materials on Mars would be prohibitive for early settlements.
  - **Alternative Energy Sources**: 
    - **Solar Energy**: Mars receives less sunlight than Earth, but solar power has been used by numerous Mars missions. However, dust storms can severely affect efficiency.
    - **Nuclear Power**: While nuclear power could be more reliable, current plans involve bringing nuclear material from Earth, like plutonium for RTGs (Radioisotope Thermoelectric Generators) used in rovers, due to the lack of known Martian sources.
    - **Geothermal Energy**: There's potential for geothermal energy, especially around areas like Gale Crater or other volcanic regions, but this would require deep drilling which is still speculative.

- **Future Prospects**: 
  - If Mars does have fissionable materials, they might be buried deep or in forms not easily detectable by current exploration methods. Future missions might uncover more about Mars' subsurface composition, potentially revealing if there are economically viable deposits.

- **Current Use**: For now, Mars exploration relies on energy brought from Earth or generated through solar means. The use of fissionable materials for energy on Mars would require significant technological development and infrastructure, which is not currently in place or planned.

In summary, while Mars might theoretically have some fissionable materials, there's no current confirmation or practical plan for their use in energy production due to the complexities involved in their extraction and refinement. The focus remains on solar and nuclear power systems brought from Earth for Martian energy needs.

 

[Pthigrivi]

8 minutes ago, darthgently said:

It occurs to me that if there is to be a substantial Optimus bot workforce that will be a big electrical load on its own

Does Mars have accessible fission material?  Launching reactors with no fuel could be a lot less regulated

I should do some more reading but remember hearing there’s more Thorium than Uranium which is interesting. 

[darthgently]

Given the success of Ingenuity that many thought was pointless, maybe wind might be something.  But I doubt it.  They’d likely grind themselves to scrap on the dust and would be high maintenance sweethearts for sure

Edited yesterday at 05:24 AM by darthgently

[tater]

I think Shotwell's husband is actually a nuke-E.

[farmerben]

It is affordable and safe enough to ship HEU from Earth to Mars.   What is less affordable is producing batteries on Earth and shipping all that mass to Mars.  I have no idea how the Martians will make batteries, but that seems like something way down the list of industries they will be capable of.  

[AckSed]

10 hours ago, Pthigrivi said:

The energy density of nuclear fuel is so attractive. I'm sure it's part of the mix. I feel like Mars and the moon are too geologically dead to provide geothermal? Unless you just mean thermal batteries? The latter is a great idea on the Moon where the day/night temperature cycle is so extreme.

Geothermal might work - in the right place. The Cerberus Fossae has all the signs of an active magma plume the size of the United States underneath it: https://www.sciencedaily.com/releases/2022/12/221205121545.htm

Quote

"We used to think that InSight landed in one of the most geologically boring regions on Mars -- a nice flat surface that should be roughly representative of the planet's lowlands," Broquet added. "Instead, our study demonstrates that InSight landed right on top of an active plume head."

Even if you don't use it to generate power, boring down to tap it for hab heating and factory process heat is viable, as there are companies that make heatpumps for these applications.

Ground-source heatpumps: https://www.kensaheatpumps.com/is-a-ground-source-heat-pump-right-for-you/

Overview of steam-generating heatpumps of various types: https://www.sciencedirect.com/science/article/pii/S0196890423012281

----

Regarding ISRU batteries, there are battery chemistries of differing complexities and capabilities.

The most basic would probably be nickel-iron, as popularised by Edison. Good: very tough and long-lasting, easy to make. Bad: lose charge faster than other chemistries, uses water and sulphuric acid as electrolyte.

Lead-acid is similar, but slightly better. Lead-mining on Mars is probably a no-go, though.

Molten sodium-sulphur or NAS batteries are a small fraction of grid-storage batteries on Earth, and an early electric car used them as well, because they are simple to make and use readily-available materials: steel, aluminia, elemental sulphur, sodium metal. The show-stopper is that you have to keep them hot with insulation and integrated heating elements. Not so bad on Earth, more difficult on Mars but not impossible. Personally I'd use vacuum-insulation panels or, failing that, basalt-fibre mats. Other molten-salt or low-melting metal chemistries are possible: https://en.wikipedia.org/wiki/Molten-salt_battery

---Past this point we move out of possible workshop or small factory bootstrap construction and into needing to import factory equipment.---

Lithium-iron phosphate (LFP) is the current champion of grid storage, and the elements can be obtained on Mars. It's probably even easier to make the synthetic graphite from the readily-available CO2. The electrolyte and the water used is a problem, though.

Sodium-ion batteries are a much newer thing, but already attracting attention for the availability of the base materials and the possibility of solid electrolytes. Lower energy density, though we don't particularly care if it's being used for stationary storage.

[darthgently]

Please forgive this slight diversion that is so nearly on topic wrt to nuclear sakety.  Just skip if diversion unwanted.

Spoiler

 

 

[farmerben]

The kilopower reactor generates 10 kW of power with a HEU core the size of a toilet paper tube.  That's only 13 horsepower.  

That's lawnmower scale.  Not big enough for serious digging in my opinion.  I'd say you want at least 30 hp to move 1000 lbs of material at a time even with the lower gravity.   However you have discontinuous demand for power in a digging machine, so with batteries it balances out.  At this point we don't have great battery powered tractors on Earth.

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

Edited 16 hours ago by farmerben

[tater]

A Mars colony needs megawatt or gigawatt reactors.