Caves as Initial Footholds on Mars

tahanson43206 · 2022-12-15 08:03:04

For Steve Stewart, Calliban, kbd512 and all working on the Caves topic ...

My Hacienda is set up as a framework for organizing businesses to blend together to support a viable, first tier civilization on Mars (or off Earth generally).

The plotmaster is a list of specializations around which entrepreneurs can build long term businesses.

http://newmars.com/forums/viewtopic.php … 75#p154875

If the plotmaster needs to be updated to reflect the inventive work going on in this topic, please let me (or SpaceNut) know what specializations need to be added.

Thanks again to Moderator RobertDyck, who set up the topic back in the day.

(th)

Calliban · 2022-12-27 18:28:51

Switzerland has 374,000 bunkers! Building bunkers is a long standing Swiss tradition.
https://m.youtube.com/watch?v=9bPIaHg11mI

If there is to be a Martian civilisation, it will take this to an entirely new level. Practically all living space will be underground. On Mars, underground structure will be about maintaining air pressure, protection from radiation and retaining heat. We also need the excavated rock to build roads, railways and landing pads.

SpaceNut · 2022-12-27 18:36:08

The main thing is dual use of resource brought to mars are the same ones we need to mine mars for resources to be able to expand human shelters and colony size not only short term but for its future expansion as well.

Calliban · 2022-12-28 11:10:36

A woman builds herself an underground house. This clearly took her a while.
https://m.youtube.com/watch?v=ILiIzqsfSbo

On Mars, we could create habitable spaces this way, if we dig down more than 2m and install an airlock.

Last edited by Calliban (2022-12-28 11:12:36)

Void · 2022-12-28 12:16:29

I agree. If you have the right soil/rock conditions and the water table is not high, lots of space might be created, perhaps economically.

Done

SpaceNut · 2022-12-28 16:26:51

I have seen many of these videos on Youtube to show how to build with next to nothing, but the size is tailored to ability and materials as well as time to make it so that you are protected. Mars only allows the start if you have the correct tools to do the work.

Void · 2022-12-28 19:18:54

Well, I show this "Tool" often. https://www.space.com/esa-oxygen-from-l … ation.html

You are correct, the start is its own set of troubles, and the continuation probably becomes easier.

The above tool can extract Oxygen from regolith. In the case of the Moon that is about 40% to 45% of the materials. So, now you get rid of that amount as Oxygen which you can expel from the habitat or use to a better purpose.

Quote:

In the lunar environment, the technique will split lunar regolith, which is known to consist of up to 45% oxygen, into metal alloys and pure oxygen. The moon dirt in this process is used as a cathode, the electrode through which an electric current enters the electrolytic cell, releasing oxygen in the process.

I am not so sure just how good these "Metal Alloys" are, but I would imagine some part is usable. 3D printing should make it possible to make higher quality tools with lower quality alloys.

If we find volcanic pyroclastic sediments on Mars properly cemented, then this sort of action is possible: https://en.wikipedia.org/wiki/Derinkuyu … round_city

So, if you could carve a cubic foot, (Of if you are ambitious), you put that into the machine and have it process. Sending the Oxygen to another purpose then you get to keep 40% of the space, (Sort of), and you can figure out what to do with the rest of it to make useful items. Too bad there is so much waste Oxygen. What to do?

I would imagine humans on Earth would conduct experiments on what could be produced from the 60% solids, including "Alloys".

Some chances exist for volcanic ash deposits in the Cerberus Fossae area: https://www.inverse.com/science/volcano … 0on%20Mars.

And just maybe geothermal heat, if not electricity. Even heat would be of use.

Done.

Last edited by Void (2022-12-28 19:43:44)

tahanson43206 · 2022-12-28 19:40:41

For Calliban re #54

Thanks for showing this video....

The amount of labor is impressive, since the entire project was completed with hand tools!

There is a similar cave project out on the Internet, showing a gent with power tools excavating an apartment in a sandstone cliff.

Even with the power tools, I got the impression the project took a long time, but on the other hand, when it was/is finished it has the look and feel of an apartment anywhere.

I think the examples of spacious underground facilities that Steve Stewart showed us are (perhaps) more attractive for the Mars venture.

In any case, the use of open fire that is possible on Earth seems unlikely (to me at least) on Mars.

(th)

SpaceNut · 2022-12-28 19:44:04

There are such caverns and tunnels that could hold populations of 20,000 or so in Turkey that data several thousands of years ago used for a variety of cultures to hide.

Steve Stewart · 2023-01-01 13:59:56

Calliban,
Thanks for your comments. I agree with everything you said. Actually the population of the Kansas City metro area is about 2 million. About two-thirds of Kansas City is in the neighboring State Missouri. As Kansas City grew it merged with many surrounding towns. Kansas City has a few other underground facilities. I'm not sure, but I think SubTroplis is the largest. I'll have to do some checking.

You mentioned using electric power (batteries) for mining equipment and that it would take time for the batteries to recharge. Electric machinery has been used in the Kansas salt mine (Strataca) since the 1920's. I think the equipment on Mars could be made to have batteries replaced whenever they need recharged. A set of batteries could be recharged while another set is being used, so there isn't any down time for the equipment. I agree the equipment should be running as much as possible. The equipment would need to be designed in such a way that the batteries could be easily removed and installed.

In 1948 Preston Tucker built a "car of the future" called the "Tucker". The car was innovative with many new features. One of the ideas that Preston Tucker proposed was to have a rear engine car in which the engine could be removed in a few minutes. The idea was that if someone needed engine work done on their car, they could take it to a local dealer and the dealer would swap out their engine with a loaner engine. The customer could then drive their car with a loaner engine while their engine remains in the shop being repaired.

There's are a lot of interesting stories about the Tucker. A movie was made about Tucker in 1988. For anyone interested in automotive history here's a link to the movie trailer.

Tucker: The Man And His Dream Trailer 1988

Wikipedia article "Tucker 48"

I agree Mars could use lime-like substance for road construction, eventually railroad construction and landing pads. My personnel opinion is that there should be several Martian bases spread out, rather than one huge base. All the resources a base needs will not be located in one place.

I think we all agree that a mine should be multipurpose. That is, something valuable could be mined, and the empty space left behind could be used for a habitat. I agree that sections could be sealed off and that mining can continue while more and more sections are built and sealed off. As you mentioned, a large area (2 square miles) could be mined in a relatively short time (30-40 Earth years). According to Wikipedia, Strataca is 980 acres, which is 1.5 square miles. In addition to mining salts and lime-like rock used for construction, there are other things that could be mined on Mars, such as metals like copper.
Here's what Dr. Zubrin has to say:

The Case for Mars
By Robert Zubrin
Chapter 7 Building the Base on Mars
Section: Copper
(Page 221 in my book)
Commercially, the most important sources of copper ore on Earth are copper sulfide. As we have seen, sulfur is much more common on Mars than on Earth, and it is probable that copper ore deposits are available on Mars in the form of copper sulfide deposits formed at the base of lava flows. Once found, copper or can easily be reduced by smelting or leaching, as has been practiced on Earth since ancient times.
The example of copper drives home the fact that, in general, the only way of accessing geochemically rare elements is by mining local concentrations of high-grade mineral ore. However, you will find ores only where complex hydrologic and volcanic processes have occurred that can concentrate these elements into local ore deposits, and, within our solar system, only Earth and Mars have experienced such processes. Because these processes have occurred on Mars, we should be able to find concentrated ore of nearly every metal, rare or common, necessary to build a modern civilization.

There are other ways of mining in addition to using tunnel boring machines, or drilling and blasting. Below is a segment from the PBS TV show "This Old House" that shows cutting marble with cables. I think the same technique could be used on Mars if a hard substance needed to be mined.

The Old House
How Marble is Extracted

Here are some screen shots from the video above.

Calliban · 2023-01-01 19:52:56

That marble mine is a thing of great beauty. It is a shame that we are unlikely to find it on Mars in any abundance. We know that there are magnesium carbonate deposits. But no techtonics needed to create metamorphic rock. The sand stone tested by Perseverance so far, appears to be extremely soft and crumbly. Sampling has been difficult, because samples crumble during drilling. If all Mars sandstone is like that, it will have few uses as structural material.

The saws in the video are diamond chain saws. Initially, the saw blades will be imported from Earth along with the saws themselves. In the long run, Mars has been pelted with so many carbonaceous asteroids, it should contain concentrations of micro diamonds within the regolith.

Last edited by Calliban (2023-01-01 19:54:27)

Mars_B4_Moon · 2023-04-28 04:47:15

How exploring Hawaiian caves helps NASA search for life on Mars

https://phys.org/news/2023-04-exploring … -life.html

Steve Stewart · 2023-04-29 10:37:49

When building an underground habitat on Mars it would be helpful to use a reflective barrier on the interior that reflects both light and heat. Below is an example of a radiant heat barrier that can be used in an attic, walls, or crawl space of a home. The foil liner reflects infrared rays (heat). When used on a home on Earth, it reflects heat back inside the house in the winter.

There are 3 ways in which heat can be transferred: Conduction, convection, and radiation. Conduction is when a substance conducts heat. Convection is heat transfer via the movement of air. The third method is by radiance.

When the interior of a house is warm in the winter, all of the contents in the house radiate heat in the form of infrared rays. Unless the house has a radiant barrier, the heat will go through the insulated walls/ceiling in the form of infrared rays. In the summer, when the house needs to be cooled, heat from the outside will come inside via infrared rays, increasing cooling costs. Hence the need for a radiant barrier like the one shown above. On Mars, habitats will need to be heated year round. Unless they have a radiant barrier in addition to insulation, they will lose radiant heat.

Radiant Barriers - US Department of Energy

Radiant Barriers by LP TechShield

On Earth, houses are often insulated with fiberglass. The insulation slows down the conduction of heat. Glass by itself is not a good insulator. However a fine glass fiber, with air between the fibers slows down the conduction of heat. This is because heat has a difficult time transferring across boundaries. When fiberglass insulation is used in a building, a single fiber of glass will conduct heat rather well. Heat is then transferred to the air surrounding the fiber. This creates a "glass-to-air" boundary. Boundaries like this create resistance to the flow of heat.

After a sliver of air between fibers transfers heat from one fiber to another, the heat must cross another (glass-to-air) boundary. Then from air-to-glass again, then glass-to-air, then air-to-glass, and so on. Each transfer of heat from one substance to another is a boundary. The more strands of glass fiber that are separated by air, the more boundaries. More boundaries means more resistance to the conduction of heat.

I remember about 15-20 years ago when fiberglass insulation for a 4" wall was always R11. About 12 years ago I noticed it was R13. The higher R number (better insulation) was achieved by insulation manufacturers making insulation with smaller glass fibers, which creates more boundaries.

In order to get the most from fiberglass insulation, it's important that the insulation remain loose and "fluffed up". If the insulation is compressed, it destroys the boundaries which diminish its insulation properties.

I've known people who thought they could put 6" insulation into a 4" wall (wall built from 2x4's). They saw the higher R rating for 6" insulation and thought they could cram it into their 4" wall. I explained to them that if they squeezed 6" of insulation into a 4" wall it would squeeze out much of the air, eliminating many of the boundaries, which is how insulation works. If they shoved 6" of insulation into a 4" wall they would end up with very little resistance to the conduction of heat.

Fiberglass insulation not only reduces the conduction of heat, it also limits the movement of air (convection). However it does not reduce heat transfer from radiation. This is why there are products on the market like the one shown above, to reduce radiant heat loss. On Mars, coating the inside of a habitat with some type of foil, like the one shown above, would reduce radiant heat loss. The foil would also reflect light, which would make more efficient use of light, particularly in growing areas for plants.

Efficient use of light in a Martian habitat

Farmers are well aware that one form of waste is the waste of light. When growing crops, the idea is for as much sunlight as possible to shine on plants to produce crops. Any sunlight reaching the ground it is waste. In a Martian habitat, any light reaching a wall, ceiling, or floor, and is absorbed is waste.

This is why crop spacing is so important. If crops are spaced too far apart (too few seeds planted per acre), sunlight goes between the plants, reaches the ground, is absorbed and wasted. If crops are planted closer together (more seeds per acre), less, or no light is wasted. It only makes sense that if a farmer plants 5% more seeds he'll end up with 5% more plants, resulting in 5% more crops, and 5% more profit. This is only true to a point, until all the sunlight is used.

Most field corn has 1 or 2 ears of corn per stalk. When corn is spaced farther apart, more stalks will have 2 ears. Even though each stalk has more ears, the farmer will end up with less corn due to having fewer plants.

If corn is spaced too close together, many stalks will end up with 1 small ear, due to not enough light. Even though they have more plants, they'll end up with less corn because the stalks only have 1 ear and they are smaller. In this case farmers are buying more seed and are ending up with less corn. Here in Kansas, most farmers I know plant about 28,000 seeds per acre for corn. Planters have adjustments on them to adjust the number of seeds planted per acre.

Of course there are many other variables in addition to crop spacing, such as weather (temperature), soil condition, amount of rainfall, etc. More plants require more water and consume more nutrients from the soil.

On Earth and on Mars, seed spacing is important for all plants, not just corn. On Mars, plants will need to be spaced properly for maximum production. Seed spacing on Mars will be dependent on the amount of light available, along with the other factors just mentioned.

Farmers use seed flow monitors on their tractors to count the number of seeds being planted per acre in real time. Below are a couple of seed flow monitors manufactured by Sensor-1, a former employer of mine.

Below is a seed flow monitor by DICKEY-John. This type of seed flow monitor was first produced in the 1960's. Below that is a John Deere monitor, also manufactured by DICKEY-John. Each light represents one tube (one row) on the planter. The DICKEY-John monitor shown has 12 lights. It is made for a 12-row planter. The John Deere monitor shown has 8 lights and is for an 8-row planter.

When seeds fall through a tube on the planter it makes the corresponding light flash. A light that is not flashing means that a row is not planting (a tube on the planter is clogged, or something else is wrong). Without a seed flow monitor a farmer could end up planting a field of crops with one row missing.

All of the monitors shown have an alarm that sounds whenever a light isn't flashing (a row isn't planting). It's much like a smoke detector alarm. The DICKY-John monitor shown has an alarm in the bottom left corner. The John Deere monitor shown also has an alarm near the bottom left, and also has a red light (below the John Deere logo) that comes on when a row isn't planting.

How Far Apart Should You Plant Your Vegetables?

5 Reasons Why Proper Plant Spacing Is the Best Thing You Can Do for Your Garden

Proper Plant Spacing and Why it Matters

Why You’re Missing Out When You Don’t Monitor Every Run on the Drill!

If habitats on Mars were to use a radiant barrier like the one that was shown above, it would not only help insulate the habitat, it would also reduce the amount of light wasted. This is true in both living areas and areas used for growing plants, and is true in habitats above and below the surface. If a radiant barrier were not used, an underground habitat that was light in color (such as the one shown above in post#60) would help reflect more light, which would waste less light than an underground habitat that was dark in color.

SpaceNut · 2023-04-29 11:08:01

Thank you for the post as it has given me some thoughts as to what also can be done for my home.

tahanson43206 · 2023-04-29 11:09:10

For Steve Steward re #63

SearchTerm:Radiant heating reflector
SearchTerm:Barrier radiant heating
SearchTerm:Crop spacing with examples of farm equipment
SearchTerm:Spacing seeds and of rows for optimum growing success agriculture

(th)

Steve Stewart · 2023-04-30 05:13:30

Tahanson #65
Thanks for the search terms. I never think to use them.

SpaceNut #64
I think IR (infrared) barriers do work. The first time I bought a house it had infrared barriers and my utility bills were always low, and I don't think my furnace was all that efficient.

The link I mentioned (Radiant Barriers - US Department of Energy) in post#63 pointed out that a radiant barrier in the attic would make the attic cooler in both the summer and winter. In the summer that is desirable, but in the winter it would be a bit of a disadvantage because it would reflect heat (infrared rays) from the sun and would keep the attic cooler. I don't think that's much of a disadvantage as long as the attic is well insulated.

Heat flow is always proportional to temperature difference. That is, the greater the temperature difference between two objects, the greater the heat flow from the warmer object to the cooler object. This is true regardless of the type of heat flow (conduction, convection, or infrared) and regardless of the amount of insulation between the two objects. In the winter, more heat will be transferred from the living area to the attic when there is a larger temperature difference between the two (A cooler attic will receive more heat from the living area than a warm attic). Good insulation will reduce the amount of heat loss, but it still will be more with a larger temperature difference than with a smaller temperature difference. Again, I think the loss is minimal as long as the attic is well insulated.

SpaceNut · 2023-04-30 10:11:59

The ability to use low tech on mars to build underground will be important to reduce energy requirements.

Mars_B4_Moon · 2023-09-27 13:30:41

Chinese Astronauts May Build a Base Inside a Lunar Lava Tube

https://www.universetoday.com/163371/ch … lava-tube/

Caves were some of humanity’s first shelters. Who knows what our distant ancestors were thinking as they sought refuge there, huddling and cooking meat over a fire, maybe drawing animals on the walls. Caves protected our ancient ancestors from the elements, and from predators and rivals, back when sticks, stones, furs and fire were our only technologies.
So there’s a poetic parallel between early humans and us. We’re visiting the Moon again, and lunar caves could shelter us the way caves sheltered our ancestors on Earth.

Steve Stewart · 2023-09-29 00:34:32

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Steve Stewart · 2023-09-30 00:13:49

Content moved

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Void · 2023-09-30 14:35:58

Steve Stewart, I have reviewed, #69 a bit. Just now I do not do anything that is likely to raise my blood pressure so my focus is not good, it is seldom good. I had a very minor stroke a few days ago, so that is why I am not willing to drill too hard and too deep. I do not seem to have permanent damage, I feel as though I am as I was, but I was told the my body had been challenged so, I am taking everything slow and changing my habits and getting medications for my condition.

About #69:

My current interest has been Lava Tubes, and also sintering objects from regolith. It seems to me that a Lava Tube might do for the Main Shaft, unpressurized. I do like that you then can make side shafts, each with different potential environments and uses. At least that is what I think i read.

I may suggest things, that you have already worked with but I am thinking microwave drilling might be suitable for making your side shafts.

https://spectrum.ieee.org/altarock-ener … rmal-wells
Quote:

AltaRock Energy is leading an effort to melt and vaporize rocks with millimeter waves. Instead of grinding away with mechanical drills, scientists use a gyrotron—a specialized high-frequency microwave-beam generator—to open holes in slabs of hard rock. The goal is to penetrate rock at faster speeds, to greater depths, and at a lower cost than conventional drills do.

Quote:

In trials, millimeter waves have bored holes through granite, basalt, sandstone, and limestone.

So, this looks good for low gravity rocky worlds like the Moon and Mars, probably Mercury, likely Vesta the asteroid.

I am hoping that the process would vitrify the linings of the tubes to seal cracks and also to seal sandstone on Mars.

And I think that drilling living space will be much easier than drilling for Geothermal.

From #70, I see that you are doing the main shaft vertical? Lava Tubes of course will be more horizontal, but so what we could go vertical from a lava tube. Actually, if the Moon has veins of lava that have more Carbon and Water that would be a double win. Things I have read indicate that as the Moon cooled, volatiles would be pushed from the crystalizing material into the remaining less viscous lava.

So, we might want to locate the latest lava and see if it has much. The Moon should not be uniform there could be veins of volatiles. With drilling also, it might be possible to intercept a deep crack and intercept gasses coming out of the Moon such as Argon.

Quote from the previous link:

“Today we have an access problem," says Carlos Araque, CEO of Quaise, an affiliate of AltaRock. “The promise is that, if we could drill 10 to 20 km deep, we'd basically have access to an infinite source of energy."

So, I presume we may drill much deeper on these rocky worlds, including Mars. If so, then the living spaces can be enormous.

Plese let me know what things I have missed in your intentions.

Done.

Last edited by Void (2023-09-30 15:01:35)

Void · 2023-09-30 16:05:38

For Mars, we might suppose to reach liquid aquifers. If not, that then perhaps vapor aquifers which may lie above liquid aquifers. Speculation of course. If liquid aquifers do exist quite deeply, then it may be that the water being salty and cold, may not boil, especially if there is a greater air pressure.

So, down there, three phases of water may exist. And so, a water laden atmosphere may exist. So, perhaps one could drill for vapor. Just a speculation.

Your notions may facilitate a base to do that.

Done.

Last edited by Void (2023-09-30 16:08:37)

Void · 2023-09-30 19:04:56

This makes me wonder about all the rocky worlds including Vesta.
https://spectrum.ieee.org/altarock-ener … rmal-wells
Quote:

AltaRock Energy Melts Rock With Millimeter Waves for Geothermal Wells The Seattle-based company received an ARPA-E grant to test and scale its technologyMARIA GALLUCCI19 FEB 20203 MIN READ

Quote:

“Today we have an access problem," says Carlos Araque, CEO of Quaise, an affiliate of AltaRock. “The promise is that, if we could drill 10 to 20 km deep, we'd basically have access to an infinite source of energy."

Last edited by Void (2023-09-30 19:12:56)

Steve Stewart · 2023-09-30 19:06:16

Gosh Void, I'm so sorry to hear about you "minor" stroke. I hope you get better. I tell everyone to do whatever the doctor says. I had surgery recently and I did whatever the doctor told me. Everything turned out okay. Hopefully everything works out for you too, I wish you the best.

I've seen some of your posts about lava tubes, I know it's a subject that comes up in various articles, documentaries, news clips, etc. No doubt you have looked into lava tubes more than I. Those are good links about ways of drilling too. Thanks for the info.

I've tried to keep post #69 and #70 more general, not specific to one application only. It's more of a general concept. I know this thread is about "Caves as a foothold" but the basic concepts of #69 and #70 could be applied to above or below ground.

You asked about the "Main shaft being vertical?". Actually it's not specified. The "Main shaft" could be deep underground with an elevator going to it, like the salt mine in Hutchison Kansas. Or the "Main shaft" could be shallow underground, and it could be a road with a gradual incline to the surface. Or it could even be an above ground. Possibly a "Quasi-hut" (Quonset hut) type structures built out of rock above ground. In that case, I would think the inside would look similar to the pictures you posted in #57. If a "Quonset hut" type structures were built on the surface and covered with regolith they would be similar to tunnels built underground. They would be protected from radiation and large temperature swings.

One of the things I'm trying to show with the frost line (Figure 70.1 and 70.2), is that it's easier to heat each segment, if there is a heated segment on each side. I think it was Calliban that pointed this out at one time, that a building has 6 sides. (Floor, ceiling, and 4 sides: North, South, East, West). If the segments are located next to each other, then the sides of the middle segments do not lose any heat (or lose very little heat). Segments in the middle only need heat on 4 sides, not all 6 sides. Having segments bunched up together allows there to be more area that requires less heat.

One of the advantages of lava tubes is that material doesn't have to be removed to create an open space. That's a big advantage that conserves a lot of energy, equipment, and time, etc. A disadvantage that I see with lava tubes is that their geometry is probably less than ideal. There probably are not segments off of a main shaft that are bunched up, but separated, so that they are easier to heat.

Even if lava tubes are less efficient to heat, the fact material doesn't have to be removed, should be more than enough to offset the extra energy required to heat them.

Several smaller habitats could be built in a large lava tube. The lava tube would still provide protection for the habitats. That would be another option. I think what I have proposed here, in #69 and #70, is compatible with all of these options.

Steve Stewart · 2023-09-30 19:15:13

Maybe I should explain the geometry of a habitat a little bit.

As an example, imagine a room that is square with four 10' sides. The area inside the square room is 100' square feet. (10' x 10' = 100' square feet).

Now imagine a rectangular room that is 4' wide and 25' long. It also is 100' square feet inside.
(4' x 25' = 100' square feet).

Notice that the rectangular room has much more wall space than the square room. The circumference of the square room is 40' (4 walls x 10' each)

The rectangular room has two 25' long walls, for a sum of 50', and two 4' walls for a sum of 8'. The total circumference for the rectangular room is 58'.

When we look at the area of the walls in both rooms, we realize that it takes more heat to heat the rectangular room, than it does the square room. This is because every square foot of wall space will lose a little bit of heat. The more wall area there is, the more heat is lost. It turns out the a square room has the most area inside, with the least amount of area of the walls. (Hope that makes sense)

The trick is to make the room inside as big as possible, while keeping the surface area of the room as small as possible. When the ratio of the room inside, to the surface area, is as high as possible, then that geometry requires the least amount of heat. (Might need to stop and think about that one).

In Kansas there are a lot of old farm houses that are two stories tall and look like big boxes. They are about as tall as they are wide, and they are as wide as they are long. People from out of State often ask why Kansas has so many "big box houses"?

The reason is that a big box has the most area inside, for the least amount of surface area on the outside. Keeping the outside surface area to a minimum means less heat loss in the winter, and less material (studs, siding, paint, etc) to build the structure, for the most amount of space inside.

When looking at two dimensions, the shape that has the most area inside, and the smallest circumference, is a circle.

In three dimensions, the shape that has the most volume inside, and the smallest surface area, is a sphere.
Hope that makes sense.

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