Caves as Initial Footholds on Mars

Calliban · 2022-12-10 18:10:37

Void, the sedimentary layer between the two basalt layers may be a good option. The excavated cavern would have a strong basalt ceiling.

Another possibility is Mount Sharp in Gale Crater.
https://en.m.wikipedia.org/wiki/Mount_Sharp

This is a sedimentary rock deposit as tall as Everest. The sand in the crater is up to 3% water by weight. This provides a valuable water source for agriculture. Time will tell.

So far as cutting sandstone is concerned, a pneumatic drill will produce irregular blocks. Some of these could be cut into more precise shapes for other uses.

Last edited by Calliban (2022-12-10 18:12:56)

Void · 2022-12-10 20:02:45

Good stuff for sure. Just Mt. Sharp, the scale of it. And then look at the layers displayed by Valles Marinaris.
https://mars.nasa.gov/resources/3874/valles-marineris/
Some volcanic deposits are also suitable for carving:
https://www.guidedistanbultours.com/the … l%20around.
https://en.wikipedia.org/wiki/Derinkuyu … round_city
I believe that that is in volcanic ash layers.

I have considered swimming pool sized domes on the surface, with swimming pools in them.
Even a sink trap type deal where if the dome leaked, people could swim down to the bottom, and then down the drain into a trap to lead into a cave. Possibly 1/3 bar pressure pure Oxygen in the swimming area, and 2/3 bar in the caves, O2, N2 mix. Not sure how healthy that would be.

As for the bends, maybe going up could be handled properly. You would not need to hesitate to go down. I think I recall that Robert Dyck had a notion of a similar transition where bends might not happen.

When not in use as a swimming and rest area, the pool might grow duck weed. Perhaps some method to push it into a bundle for a bit while it is a swimming pool?

Anyway, might be an OK way to clean up, provided no disease vectors took hold. Might help with mental health. Perhaps trees or bushes planted around the perimeter.

Something to work on.

Done.

Last edited by Void (2022-12-10 20:15:25)

Steve Stewart · 2022-12-11 14:06:58

Thanks everyone for your links and comments. The pictures and videos remind me of the salt mine in Hutchinson Kansas (called "Strataca"). Strataca is a salt mine that is still in operation today, as well as a museum that is open to the public. I last visited Strataca about a year before the pandemic. I'd like to share some of my personnel pictures I took while visiting the salt mine. Its address is 3650 E Ave G, Hutchinson, KS 67501. The above ground entrance can be seen on Google street view.

The above ground building has a lobby with a map of the salt mine. It shows dates of when sections were mined. Tunnels in the mine are 50 feet wide (15.2 meters) and 10 feet tall (3 meters). They run North-South and East-West. "Pillars" are 40 feet square (12.2 meters square) and are seen as small squares on this map. Salt is being mined using the room and pillar method. The mine is located 650 feet (about 200 meters) below the surface.

Steve Stewart · 2022-12-11 14:08:27

There is not any reinforcement holding up the ceiling. The salt has enough plasticity to hold itself up. The ceiling is slowly sinking at a rate of 1" per 1,000 years.

On Mars, I don't think an underground facility would have a problem with cave-ins, rather I think the problem would be with "blow outs". A Mars facility could be made air tight with a layer of rubber applied to the walls, ceiling, and floor. I picture the rubber looking something like roofing felt. (Sometime in the future I'll post my proposal on how to make rubber on Mars. I'm still working on it).

When pressurized, the rubber would be pressed tight against the walls and ceiling. A layer of aluminum foil could be put on top of the rubber so as to reflect light. The aluminum foil would not only make more efficient use of light, but would also help insulate the facility by reflecting inferred rays. Airlocks could be used between different sections of the facility. Part of the facility could be in operation while more mining is done to expand the facility.

Steve Stewart · 2022-12-11 14:10:05

The floor is coated with a special type on concrete made from salt, called "Salt-crete". Salt is used as the aggregate, in place of sand and gravel. This greatly reduced the amount of weight that had to be transferred into the mine to create a concrete floor.

I find it interesting that the salt-crete does not have any cracking, even though there aren't any control joints. I couldn't even find miniature cracks when I inspected it closer. Apparently the constant temperature and humidity of the mine prevents the salt-crete from cracking. I didn't think to ask if any rebar or mesh was used. Abandoned tracks that once hauled salt can be seen here.

Steve Stewart · 2022-12-11 14:11:06

Strataca has a saying "Everything that goes in the mine stays in the mine", as stated on this display. Because of the costs of hauling trash to the surface, trash is left in the mine.

The mine is at a constant temperature of 68F (20C) and low humidity year round, without any heating, cooling, or humidity control. Anything kept in the mine is persevered. The mine contains trash, such as Campbell Soup cans from the 1920's and 1930's, which are perfectly persevered.

Trash left in the mine includes human waste.

Steve Stewart · 2022-12-11 14:12:10

Because of the constant temperature and humidity of the mine, many Hollywood artifacts are stored here. The original copy of the movie "Wizard of OZ" is stored here, as is Dorthy's dress used in the film. Medical records are stored here too. Our tour guide told us that if you have ever seen a doctor in the State of Kansas, more than likely your name is in this mine.

Steve Stewart · 2022-12-11 14:13:37

All equipment used in the mine must first be disassembled and lowered into the mine. Brand new equipment must be disassembled into pieces small enough to fit on the elevator. Once in the mine, the equipment is then reassembled. When the equipment is worn out, it is not hauled to the surface to be discarded. Instead it is left in the mine indefinitely.

"Everything that goes in the mine stays in the mine"

That's me on the right.

Steve Stewart · 2022-12-11 14:14:52

This is a "chain saw" that was used in the mine, it's called an "under-cutter". It was used to under-cut the very bottom of a wall before the wall was drilled and blasted. It makes me wonder if a similar mine could be made on Mars. Using the room and pillar method, 50 foot wide tunnels could be made on Mars with overlapping bores from a small diameter tunnel boring machine. Perhaps a chain saw like this one could be used to flatten out the floor and ceiling.

The mine is still in operation today. Blasting is still done even though a small portion of the mine is opened to the public and artifacts are stored in the mine.

Steve Stewart · 2022-12-11 14:16:20

This is a tunnel that is blocked off to control air movement through the mine. Rather than hauling something from the surface to block off areas, left over boxes that carried explosives are filled with salt and then used to build a wall.

Steve Stewart · 2022-12-11 14:17:32

Hutchinson Kansas is not only home to the salt mine Strataca, it's also home to the space museum "Cosmosphere". The Cosmosphere has Gus Grissom's capsule the "Liberty Bell 7" on display. The Liberty Bell 7 sank in July 1961 and was recovered from the Atlantic Ocean in 1999. The Cosmosphere also has this replica of the Mars rovers Spirit and Opportunity.
If anyone is passing through Hutchinson Kansas my advice is to visit both the salt mine and the Cosmosphere. Both could be done in one day but I'd recommend an overnight visit.

Links for more information:

Strataca: The underground salt museum

Cosmosphere Space Museum

The Sinking of Liberty Bell 7: Gus Grissom’s Near-Fatal Mission

Things to do in Hutchinson Kansas

Both Strataca and the Cosmosphere Space Museum have Facebook pages.

kbd512 · 2022-12-11 15:28:23

Steve,

If you had a grinder to smooth out the walls / ceilings / floors of the excavated caverns, then a very thin tape of fiber-reinforced plastic could hold air pressure. This implies smooth flowing transitions, though (no square or rectangular chambers). Lay unidirectional fiber tapes along the interior of the cavern and you have a very strong air-tight seal (the epoxy resin could be cured using UV light or heat and pressure). A locally made Basalt fiber could serve as a substitute for Carbon Fiber. Modern airliner fuselages / pressure vessels and wing boxes from Boeing and Airbus are made using unidirectional CFRP tapes wound over a mold. In this case, the cavern walls serve as the outer mold line for the layup.

Void · 2022-12-12 14:02:04

That seems like valuable input kdb512.

------

There is apparently at least one salt dome on Mars: http://martinhovland.weebly.com/mars.ht … sists%20of

Quote:

At the foot of the giant Hebes Mensa salt dome on
Mars, there is a feature called the "Oil Spill" (Adams
et al., 2009). But, ccording to Adams et al., it consists of
liquid brines that have been coloured black by dark dust particles.
However, - this is not be true.

Image Quote: http://martinhovland.weebly.com/uploads … 256672.jpg
I see no value in arguing the case for or against oil on Mars at this time. But we may know a place to check, and that place appears to have a salt dome.

Having notions of where there may have been seas on Mars, gives a notion of where else salt domes might possibly exist.
https://www.bing.com/images/search?q=se … HoverTitle
Image Quote: https://th.bing.com/th/id/R.48c6dcee931 … ImgRaw&r=0
That is a very good Mars map.

In the North and Hellas, for the most part I suppose. But the Mariner Rift Valley may have been part of a northern sea, which may be why there appears to be a salt dome there.

Just possibly the recently discovered volcanic possibilities for Mars, may include salt domes.
https://en.wikipedia.org/wiki/Elysium_( … -7.5%C2%B0.

Quote:

Elysium, located in the Elysium and Cebrenia quadrangles,[1] is the second largest volcanic region on Mars, after Tharsis[2].[note 1] The region includes the volcanoes (from north to south) Hecates Tholus, Elysium Mons and Albor Tholus.[3] The province is centered roughly on Elysium Mons at 24.7°N 150°E. Elysium Planitia is a broad plain to the south of Elysium, centered at 3.0°N 154.7°E.[4] Another large volcano, Apollinaris Mons, lies south of Elysium Planitia and is not part of the province. Besides having large volcanoes, Elysium has several areas with long trenches, called fossa or fossae (plural) on Mars. They include the Cerberus Fossae, Elysium Fossae, Galaxias Fossae, Hephaestus Fossae, Hyblaeus Fossae, Stygis Fossae and Zephyrus Fossae.

Perhaps lava tubes and sedimentary rock layers as well in the region.

Done.

I like to understand where stuff is: https://www.bing.com/search?q=Cerberus+ … 5425faf582
Image Quote: https://www.dlr.de/content/en/images/20 … normal&v=4

So, an ancient sea floor, and possibly new volcanism.

Geothermal perhaps.

Done.

Last edited by Void (2022-12-12 14:22:36)

Steve Stewart · 2022-12-12 17:11:00

Kbd512,
Thanks for sharing your ideas. I'm curious, what do you do for a living? What is your area of expertise?

Steve Stewart · 2022-12-12 17:12:33

Void,
Thanks for commenting. I have never heard of the "Oil Spill". Those are good images too. Thanks for sharing. I'll read into it more when I get a chance.

I've been reading some of your comments on your thread "Worlds, and World Engine type terraform stuff" as well as some of your other posts. You're quite the creative thinker and creative writer. Have you ever thought about self publishing a book?

Below is a YouTube video for a "Espresso Book Machine". There are several ways of self publishing. I'm just now starting to learn about it. I don't know that "Espresso" is the best way to self publish, but at least the video shows how self publishing works. Even if you only sell one book as a "vanity copy" it's perfectly acceptable. You're only out your time in writing the book. Something I think you and a few others on this forum should think about. Give it some serious thought.

https://www.youtube.com/watch?v=qJUla8xJ5BM

Void · 2022-12-12 20:07:47

Steve Stewart, thanks for the consideration:

Void,
Thanks for commenting. I have never heard of the "Oil Spill". Those are good images too. Thanks for sharing. I'll read into it more when I get a chance.
I've been reading some of your comments on your thread "Worlds, and World Engine type terraform stuff" as well as some of your other posts. You're quite the creative thinker and creative writer. Have you ever thought about self publishing a book?
Below is a YouTube video for a "Espresso Book Machine". There are several ways of self publishing. I'm just now starting to learn about it. I don't know that "Espresso" is the best way to self publish, but at least the video shows how self publishing works. Even if you only sell one book as a "vanity copy" it's perfectly acceptable. You're only out your time in writing the book. Something I think you and a few others on this forum should think about. Give it some serious thought.
https://www.youtube.com/watch?v=qJUla8xJ5BM

I have a relative who does religious books, perhaps that person can also consul me, if I decide to make an effort.

I will copy this text to a place I can reference, as I don't want to loose it.

Done

Last edited by Void (2022-12-12 20:08:22)

Calliban · 2022-12-13 09:22:46

Some very interesting material on the Kansas salt mine Steve.

Regarding the need for a lining on the cavern walls; if the concern is to seal small cracks that could leak air then some sort of polymer paint might be the easiest option. Ideally, we want something that can be sprayed onto walls with minimal labour cost.

We can use the thin wall pressure vessel equation to estimate the tensile strength needed for a polymer coating. Assume a 1mm layer thickness and a 1mm crack width. Assume a 50KPa pressure difference.

Minimal tensile strength = PR/2t
TS = 50,000 x 0.001 / 2 x 0.001 = 25KPa.

Pure polyethlene has a yield strength of about 20MPa. This tells us that it should be easy to develop a coating that has sufficient strength to seal small leaks. The salt itself may be a sufficient coating if applied as an aqueous preparation. Deep excavations should offer a natural protection from this problem, as the rock is under several MPa of compressive stress. This should prevent crack growth under internal pressure and would tend to naturally close cracks. A bigger danger would appear to be cave-ins. This is a standard structural engineering problem that isn't unique to Martian conditions. Discontinuities in the rock structure could pose a risk.

Any mined out salt would be useful on Mars as a means of gathering water. Salt is hygroscopic. Salt exposed to Martian air will gradually absorb water vapour, which can then be removed by heating.

Last edited by Calliban (2022-12-13 10:04:08)

Void · 2022-12-13 11:48:20

Calliban,

This suggests that salt domes are fairly impermeable.

https://www.howardfenstermanminerals.co … rmeability.

Quote:

Underground Storage and Waste Disposal
When the salt, sulfur and hydrocarbons are extracted, this leaves large holes which can be used for underground storage. Some of the mines which are developed into salt domes are sealed and can be used for the storage of oil and gas. In the US and Russia, salt domes also serve as state reservoirs of helium gas. This is because salt is the only type of rock that has very low permeability. As a result, it can hold the tiny atoms of helium gas.
Since salt has low levels of permeability, it also restricts the flow of any type of liquid into the soil. These properties make salt domes very effective for the disposal of hazardous radioactive waste.

I wonder if a combination of a plaster of salts, and your proposed coating would help for lava tubes and for caves carved in sedimentary rock.
Perhaps squirting salt into the cracks as the first preparation?

I wonder about vacuum grease as well: https://en.wikipedia.org/wiki/Vacuum_grease

I wonder if various types of a combination of vacuum grease and salts might give some results, and then be covered with the film you proposed, or a tape like kdb512 proposed?

Maybe the crack filler, then the tape, and then perhaps the film.

Done.

Last edited by Void (2022-12-13 11:58:57)

kbd512 · 2022-12-13 13:41:25

Steve,

I work on forecasting tools. I primarily implement Oracle-based supply chain management software as a consultant for large corporations that make industrial (steel, oil and gas) or consumer products (raw foodstuffs and processed food products, beverages- soda / tea / coffee / fruit juices / alcohol, pharmaceuticals and biomedical devices, appliances, electronics, basically all the stuff people buy / consume in mass quantities). I do a lot of pl/sql programming and data analysis, I use various other general purpose programming languages for writing software (mostly related to supply chain management, obviously, and sometimes a few "fun" projects here and there). I've worked on forecasting tools since about 2007. It pays the bills and their forecasting problems are all different enough to hold my interest, so that's what I do. Supply chain management is over-glorified bean counting in some ways, but not really finance. Those gosh darned beans won't count themselves, though, so that's where I come in .

So, nothing to do with engineering, unfortunately . However, I find structures and energy very interesting. I'm an enthusiastic amateur at best. If I discover through basic analysis that any particular idea is technically unworkable or impractical then I will abandon that idea and move on to the next idea. Trying to force round pegs into square holes isn't appealing to me. I would assume "real engineers" do the same thing, as I assume their goal is to get a job done reasonably safely and with minimal cost / fuss so they can move on to the next task.

I proposed a fiber-tape based solution because with the correct kinds of fibers, an exceptionally strong and durable sealing layer can be had. Maybe Kevlar or Twaron are better fiber choices, though. Twaron has low creep, a modest and slightly negative CTE, low thermal conductivity, nowhere near as sensitive to strain rate as E-glass / S-glass / CFRP. That last bit may not be all that important for a structure which hopefully has very little dynamic loading, but it's nice to have anyway. Maybe someone will drop something heavy on it or ram something into a wall by accident. All types of glass / graphite / basalt fibers have brittle failure modes, so those are sub-optimal even though they may be perfectly adequate in many cases, maybe for upper walls and overheads where impacts are unlikely to occur. No matter how good their tensile strength or strength-to-weight is, Kevlar or Twaron in tension, which it will be from internal air pressure, is similar in tensile strength to Carbon Fiber but without GF / CF brittle failures. It's a lot harder to snap Aramid / para-Aramid fibers, and it could function as a "tattletale" to warn engineers of impending failures.

With routine inspections, sections of rock / salt that crack / pulverize and yield slightly can be cut out and replaced with spot-reinforcement cement / concrete mix loaded with 1% to 2% chopped CNT fiber (cheapest and easiest to produce). This CNT filler is now used commercially in certain rail yards and airport runways or taxiways because regular or even steel-reinforced concrete has been cracking within 6 months of initial usage due to the crushing weight of airliner or rail traffic. Maybe it's bad material or bad design or simply loose topsoil that gets washed out with heavy rain, but materials technology has a pretty good solution for our less-than-ideal real world. They've been able to go 2 years or more in these busy rail yards that wouldn't last 6 months before regular concrete had to be replaced. That's a remarkable strength and fatigue life improvement for a product that costs less than rebar-reinforced concrete which also failed. No word yet on using this stuff in building foundations or bridge sections, so I guess those still mandate the use of rebar-reinforcement and/or a pre-stressed design. That, or it's not proven well enough yet.

The basalt fiber idea was suggested because that precursor material is readily available on Mars. The basalt and Sulfur are all over the place on the surface. Basalt's primary advantage is not transporting it from Earth to Mars. However, there are better synthetic fiber reinforcement options available if we either bring along our own Acme petrochemical refinery starter set or import the fiber from Earth, and possibly only make the plastic on Mars using locally-synthesized Methane. Methane from fracking is now used to produce much of the plastic made in America, rather than the crude oil-derived plastics which are more common in the rest of the world.

If you have Oxygen / Hydrogen / Nitrogen (very hard to come by on Mars) / Carbon and Sulfuric acid, then you can make Aramid and para-Aramid fibers as well. That means protective clothing for working near hot materials or electrical equipment, fiber-tape reinforcement, very strong and abrasion resistant (Mars also has fine abrasive dust, just not as bad as the moon due to weathering processes) ropes and chafing guards for cave / canyon / mountain exploration, cargo straps and netting, inflatable fabric surface structures (with Vectran / LCP to protect them from UV, which Aramids are very sensitive to), tow cables to pull out stuck vehicles, "soft tackle" for securing / stowing cargo and equipment aboard ships (the ability to suspend NASA's cargo transfer bags for radiation protection using food and water contained therein), sailcloth hammocks for sleeping, parachutes, thread to sew up punctured space suits, and probably other stuff I haven't thought of. Point is, fiber and plastics are "must have" multi-purpose materials. Iron sourced for steel making, while present in very large quantities on the surface of Mars, also requires very energy-intensive refining to transform, so it will probably be used sparingly, mostly for hand tools / machines / motor vehicles / communications towers. If you're outside on the surface, then you also get a nice "scattergun effect" of secondary particle radiation showers from GCR (relativistic ions) impacts on metallic equipment. You probably don't want too much of that.

It's just some food for thought. I'm sure someone out there has this all figured out.

Calliban · 2022-12-13 15:24:38

The room and pillar method appears to be most suitable where the rocks excavated are soft, i.e salt, coal, gypsum or sedimentry rock.
https://en.m.wikipedia.org/wiki/Room_and_pillar_mining

One thing that is particularly appealing about this method on Mars is that it allows air dams to be established between pillars. This obviates the need to transport rocky tailings through airlocks, as some parts of the mine can be pressurised, whilst mining access tunnels can be kept at Mars ambient. We build the base by excavating segments, say 100m aside, off of a main access tunnel. As each segment is completed, it can be sealed off of the main access tunnel by an air dam made from heaped tailings. Segments will be separated from each other by several metres of solid stone. Once a new segment is finished, dammed off and pressurised, the stone wall separating it from other segments can be tunnelled through.

The danger of blowouts would appear to me to be quite small. If we are digging through sandstone, say, at a depth of 100m on Mars, the static rock pressure will be about 10bar. Our internal habitat pressure, at 0.5bar, is substantially smaller than the rock pressure. This negates any problems of pressurised crack growth, because the caverns are always under positive pressure from the weight of the rock above. We are only cancelling out 5% of that pressure by pressurising the cabin. Things get a little more dicey if we are using loose tailings as part of gravity stabilised air dams. But still not a big risk if our civil engineers are able to correctly assess friction between the tailing particles. The Aswan dam is a gravity stabilised soil dam and is still good after more than 50 years of operations.

Last edited by Calliban (2022-12-13 15:35:23)

Steve Stewart · 2022-12-13 20:44:16

Void comment #41

Yes, do consider it. It does take a lot of effort. I have more links about self publishing if you or anyone else reading this is interested. Just message me about it on this forum. (It does pay to have friends!)

Calliban comment #42

I was thinking an underground facility would need to be sealed, but maybe that's not be the case. If the facility is deep enough, it would be hard for air to push through all that rock and make it to the surface. It might even be self sealing. If the surrounding material contained ice, I would think the ice near the walls/ceilings would melt and air pressure would push moisture deeper into the rock and then freeze, causing a seal. I'm not sure how that would work.

If a liner were needed, I would think it would need to be flexible, so if there are any shifts in the surrounding material, the liner could flex and bend with it.

I agree we need to keep labor cost (amount of time) to a minimum. I've wondered what the cost of labor would be on Mars. If we assume a crew of 6 were sent to Mars for a 4 Earth-year stay then returned to Earth, what would be the cost per hour of labor?

If we assumed the crew averaged a 50 hour work week, and multiply that by the number of Earth-weeks spent on Mars, multiplied by a crew of 6, we would know the total number of labor hours. Divide the cost of the round trip by the number of labor hours and we'd have a cost per hour.

I've not done the math, but I'd take a wild guess it'd be on the order of 1 million (US) dollars an hour. Increasing the stay to 6 Earth-years should decrease the cost per hour, but then more supplies would need to be sent. It would be interesting to see the math on that.

I agree any salt mined would be of use on Mars. Actually there are several things that could be mined on Mars that would be of value. Mining anything of value would leave a void behind that could be used for a habitat later. Such is the case with the salt mine in Kansas.

There's another place in Kansas City that used to be a limestone mine. It has been repurposed as "the worlds largest underground storage facility". There's an article in Wikipedia called "SubTropolis" about it. Do an Internet image search on "SubTropolis caves" and you'll see what I mean. They have semi's driving through there. I'll do some digging and post information about it later. A local PBS TV program did a story about it a few years ago. I bought the DVD of the story. I might be able to post some images from the DVD.

Kbd512 comment #44

Thanks for the information. I've done some data programming myself when I was right out of college. I used "Dbase III" and "Dbase IV", and later "Clipper" which was a compiler. We'll talk more about that later when I have time. Sounds interesting.

I need to run. I got in late tonight and I need to get up early in the morning. I work a lot of hours. So if I don't respond for a few days it's because I've gotten busy. I'm not ignoring anyone.

Wikipedia article SubTropolis

tahanson43206 · 2022-12-14 07:19:36

For Steve Steward re #46

Thanks for the reminder of Clipper! I haven't thought about it since (ca) 2000, when I was part of a team converting a DOS / Clipper application to Windows / SQL.

It was actually fairly sturdy (as I recall) ... my client had several hundred customer installations around the country.

***
Your estimate of time required to prepare an underground habitat seemed (as I read it anyway) to depend upon traditional concepts of who would do what.

While understandable, I suspect that by the time actual work is done on Mars, newer technology will further amplify the capability of humans, just as computers have magnified the power of individual humans today.

Knowing you have limited time, here is a link to a topic that may offer insights for future planning: http://newmars.com/forums/viewtopic.php?id=9678

I am hoping that topic will lead to business opportunities here on Earth. There are billions of people who could earn a living doing Teleoperation right now, with a bit of clever thinking by people alive today.

(th)

Calliban · 2022-12-14 09:27:21

Underground mining equipment.
https://fuchenglhd.com/blog/types-of-un … quipments/

Some of these pieces of equipment are battery-electric. Others are diesel powered. The obvious problem with BEV is that recharging time eats into productivity. Ideally, we want to run the operation 24/7. For Mars, we could modify standard diesel powered equipment to run on dimethyl ether, which can be manufactured from methanol. We also need a buffer gas, which is most conveniently provided by carbon dioxide stored as liquid. DME has a boiling point of -25°C, so can be stored as liquid under light pressure at Martian temperatures. An important advantage of this tripropellant combination is that DME and CO2 can be injected as liquids and oxygen as cold gas. This reduces the compression power requirements of the engine, improving efficiency.

The Kansas city mine is inspiring. The total floor area of the mine amounts to about two square miles. That is a sufficiently large space for a city of 100,000 people. One thing that I find interesting about this idea is that very little refined building material is needed. Most of the walls needed can be provided by excavated rock. Any additional internal construction needed can make use of cut stone blocks, bonded by clay mortar produced by wetting surface regolith. The same mortar can be used as plaster. Some people have used adobe to make furniture and built in cupboards as well.

https://www.pinterest.com.mx/pin/9007267983926868/
https://photos.hgtv.com/photo/wooden-be … style-home

As the pressurised sections of the mine will be entirely enclosed, the water used in the adobe can be entirely recovered as it dries. The surface can then be sealed by painting it with linseed, hemp or other oxygenated oil. As this polymerises, it produces an impermeable surface almost as hard as concrete. Polished earthen floors can be produced in this way as well.

Last edited by Calliban (2022-12-14 10:02:24)

Steve Stewart · 2022-12-14 17:14:02

I found the video on "SubTropolis".
The underground storage and business complex in the Kansas City metro area.
A local show called Sunflower Journeys did a story on SubTropolis a few years ago.
You can see the story at the link below.

3113:Underground and Underwater

Calliban · 2022-12-14 23:37:41

Steve Stewart wrote:

I found the video on "SubTropolis".
The underground storage and business complex in the Kansas City metro area.
A local show called Sunflower Journeys did a story on SubTropolis a few years ago.
You can see the story at the link below.
3113:Underground and Underwater

Steve, the video is interesting. It tells us something about the history of the mine. Excavation started in the 1940s. Most of the mined limestone was used for road construction. Excavation ceased when construction was completed. From this we can infer that it took 30-40 years to mine out the 2 square miles of open space within the mine. Musk wants to create a 1 million population city of Mars by 2050. An underground quarry is a viable option, requiring little construction material per unit of habitable volume. Mined out areas can be sealed off of access tunnels and pressurised as the mining proceeds. So depleted areas of the mine can be steadily converted into habitation without disrupting continued operations. It should even be possible to construct a city over multiple levels, essentially hollowing out a mountain.

I think road construction is going to be a big industry on Mars because driving over loose, dry regolith will kick up a lot of dust, which will severely degrade moving parts on vehicles. The lower gravity also complicates traction, which makes a hard road surface more valuable. Railways require solid embankments that spread point loads into the ground without subsidance. We are going to need hundreds of thousands of miles of roads and railways on Mars as we access resources all over the planet and ship them by train and truck to industrial areas close to population centres.

Another early use of any mined stone is the construction of landing pads. Because of the high temperature and extreme shearing forces imposed by rocket exhaust during propulsive landing, the pads must be constructed from strong materials. In the past, the blast from rocket exhaust has torn up large lumps of concrete from landing pads and hurled them hundreds of metres. A base constructed from large stones, topped off with fibre reinforced concrete would appear to fit this requirement. It provides a base with high compressive strength, with a tough, tensile surface that can be replaced between uses as it ablates.

Looking at the scale of construction needed to industrialise Mars, I think there will be bottomless demand for mined stone on the planet for centuries to come. Those stone mines will provide a useful secondary function as economical places to live. Mount Sharp is a sandstone deposit as large as Everest. However, it is not particularly well situated as a first generation mining site, because the product would need to traverse the walls of Gale Crater. Ideally, our mine would be in a relatively flat area, allowing stone to be shipped out by rail.

In an ealier post, Void drew our attention to a subsurface seismic analysis carried out by the insight lander.
https://www.space.com/mars-subsurface-m … wind-sound

Sedimentary rock is arranged in a layer, 30-70m beneath the surface, sandwiched between two two layers of basalt. This looks ideal. If we excavate a layer 40-50m beneath the surface, then rock pressure will be ~3bar at the roof of the mine. When pressurised to 0.5bar, effective downward pressure will be reduced to 2.5 bar, or 5 bar compressive stress within the columns, assuming a 50% volume excavation. This should actually reduce the liklihood of cave in, by reducing the downward stress acting on columns. This suggests that digging deeper does not necessarily coincide with improved safety for a pressurised mine.

Another reason for digging close to the surface would be transport economics. On Mars, fuel must be manufactured. Roadways kick up dust. For both reasons, it would be ideal to be able to remove rock and mine tailings from the mine using a railway. There are pulley mechanisms that can be used to pull rail trucks up steep gradients. But these systems have always been cumbersome. To pull laden rail trucks using a rail mounted locomotive requires progressively more power as gradient increases.
https://www.trains.com/trn/train-basics … nd-curves/

The reduced gravity of Mars should partially compensate with this, but also complicates traction. The problem is that the lower the gradient and deeper the mine, the longer the access tunnels need to be. To reach a depth of 50m at 1% gradient, would mean digging a 5km long access tunnel. Exploiting natural topography will clearly have a strong impact on the cost of establishing such a mine. This suggests that before starting any mining operation on Mars, a lot of work will be needed to identify the right location. We need rock of the right quality, that we can access through short tunnels at a shallow gradient. Ideally, we would be digging into a exposed cliff. Surrounding topography should also be relatively flat, to allow stone to be shipped out by rail. Nearby access to liquid water and geothermal heat for heat and power, constrain the choice further.

Last edited by Calliban (2022-12-15 01:05:50)

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