Optimal size for domes and other structures

[darthgently]

See Megapower section near bottom.  Apparently NASA wants something like this but doesn’t seem as fleshed out as Kilopower

https://www.nextbigfuture.com/2018/01/kilopower-megapower-reactors-would-revolutionize-energy-safety-and-space-and-military-applications.html

Grok Megapower dump:

Spoiler

NASA, along with the Department of Energy (DOE) and various industry partners, has been exploring advanced nuclear technology for space exploration, including the "Megapower" reactor concept. Here's a concise overview based on available information:

- **Megapower Concept**: The Megapower reactors are small, safe, reliable, powerful, portable, and self-sustaining nuclear reactors designed for use in remote or harsh environments. These concepts leverage lessons from NASA's Kilopower project, which was focused on smaller reactors for space applications. The Megapower reactor is intended to produce around two megawatts of electric power, which is significantly more than the Kilopower units.

- **Applications**: The primary applications for Megapower reactors include:
  - **Space Exploration**: Powering human outposts on the Moon and Mars, with the capability to operate independently of solar conditions. 
  - **Terrestrial Use**: For remote locations on Earth, like military bases or disaster relief scenarios where traditional power supply chains are inadequate or unavailable.

- **Design and Safety**: 
  - Megapower uses an innovative approach with heat pipes for cooling, similar to Kilopower, which allows for self-regulation and passive safety features. This design ensures that the reactor can adjust its power output automatically based on demand without human intervention, enhancing safety and reliability.
  - The reactor's core is made from solid uranium, encapsulated in materials like steel to form a sub-critical core, which is then surrounded by neutron-reflecting materials to sustain the nuclear reaction safely.

- **Development and Partnerships**: 
  - Los Alamos National Laboratory (LANL) has been instrumental in the development of both Kilopower and the subsequent Megapower concepts, working in partnership with NASA and DOE.
  - These projects are part of broader initiatives to develop nuclear systems for space, which also include nuclear thermal propulsion for faster space travel.

- **Current Status and Future Plans**: 
  - As of the information available, Megapower is in the conceptual and design phase, with ongoing research to mature the technology. Specific timelines for deployment were not detailed in the sources, but the focus has been on developing designs that could be implemented in the coming years for both space and terrestrial applications.

NASA's efforts with nuclear reactors, including Megapower, aim to provide a stable, high-power energy solution for future deep space missions and long-term human presence beyond Earth, addressing the challenges of power generation in environments where solar power is not consistently available.

 

[Nuke]

kilopower could barely power a modest plasma thruster array.  for spacecraft its not so much the power output as the power output to weight ratio. for a base reactor you can just throw mass at the problem. you also have a problem with getting rid of waste heat, otherwise you could run a power plant much like we run on earth. finding a cold sink on the surface of mars should be a lot easier than finding one in space. not sure what a fan and radiator can do at low pressure, but ground source may be an option, especially if you can tap into an underground ocean for coolant. if you are at the poles you could use the waste heat to extract co2 and water, but you have to keep production going while running your reactor. you might end up with a lot of surplus with no option but to vent it into the atmosphere (making new tankage for storage is bound to consume a lot of power).

[farmerben]

Even if sintering regolith works, it is probably way more efficient to create bricks than to glaze your way into a tunnel.  A 2 part vinyl epoxy spray would make brick walls airtight.

[darthgently]

42 minutes ago, farmerben said:

Even if sintering regolith works, it is probably way more efficient to create bricks than to glaze your way into a tunnel.  A 2 part vinyl epoxy spray would make brick walls airtight.

Alas, carbon is rare on the moon.  Epoxies are mostly carbon based and don’t deal with wide temperature fluctuations well.  But I’d be concerned about the temperature fluctuations in the glass also!

[Nuke]

inflatable liners might be the way to go. light, easy to ship, easy to install, no complex handling procedures that you will have to do in space suits. you could inject an epoxy or some such between the liner and the structure (or cave/lavatube) to bond it to the walls and fill in gaps. the ports would be pre-installed into the liner (think those valves you find on inflatable pool toys).

Edited January 1 by Nuke

[farmerben]

18 hours ago, darthgently said:

Alas, carbon is rare on the moon.  Epoxies are mostly carbon based and don’t deal with wide temperature fluctuations well.  But I’d be concerned about the temperature fluctuations in the glass also!

It would be worth shipping epoxy from Earth because you only need a thin layer to seal the pores of rock.  You are using it as the inner liner of your underground structure so temperature fluctuations are minimal.  It's better than inflatables because you can adapt to any geometry and at a fraction of the weight.  The airlock doors would need to be more robust than either of those.

Edited January 1 by farmerben

[darthgently]

7 hours ago, Nuke said:

inflatable liners might be the way to go. light, easy to ship, easy to install, no complex handling procedures that you will have to do in space suits. you could inject an epoxy or some such between the liner and the structure (or cave/lavatube) to bond it to the walls and fill in gaps. the ports would be pre-installed into the liner (think those valves you find on inflatable pool toys).

As amazing as plastics, epoxies, and related composites are, on the moon I really think that the scarcity of raw materials on the moon for these things are going to economically force us to optimize solutions like  glassification and concrete made from regolith.  There is carbon on the moon from meteor strikes but it is far below the concentration on earth

[Pthigrivi]

Took a stab at a cut and cover ceiling system. The idea here is to mass produce these somewhat complex concrete light-well trusses and straddle concrete coffers between them. The whole thing is then buried in reprocessed regolith to mediate temperature and radiation. The light-wells have a double glazing system with a temp and pressure controllable chamber in between both acting as an insulative buffer and allowing for either the exterior or interior glazing assemblies to be replaced without depressurizing the interior space. You just pressurize the intermediate chamber temporarily and then refill it with 6mb of argon. The interior surface of the well would be coated with a reflective liner and then the color could be corrected to the light values you'd expect from a skylight on earth with LEDs. The martian day is actually really close to the length of a day on earth so this could be synched to roughly mimic the sensation of earth daylight. Best would be to orient each of these facing the equator so they act as south or north facing light scoops. 

One question Im still struggling with is how to maintain comfortable humidity levels without the whole colony becoming stuffy and musty smelling. I've heard the ISS kind of reeks and it would take a hell of a filtration system to prevent that. Access to fresh air supply is something we really take for granted. Every surface also has to be really cleanable. Martian soil is pretty toxic because of high concentrations of perchlorates and metals and as thorough as people can be decontaminating while entering and exiting airlocks dust will inevitably get inside and cling to surfaces. Not to mention the more typical human house dust of skin, hair, and bacteria. 

Edited January 2 by Pthigrivi

[AckSed]

43 minutes ago, Pthigrivi said:

One question Im still struggling with is how to maintain comfortable humidity levels without the whole colony becoming stuffy and musty smelling. I've heard the ISS kind of reeks and it would take a hell of a filtration system to prevent that. Access to fresh air supply is something we really take for granted. Every surface also has to be really cleanable. Martian soil is pretty toxic because of high concentrations of perchlorates and metals and as thorough as people can be decontaminating while entering and exiting airlocks dust will inevitably get inside and cling to surfaces. Not to mention the more typical human house dust of skin, hair, and bacteria. 

There are some initiatives to make a bioregenerative, fully-closed life-support system: ESA has been refining a bacteriological-technological system, MELiSSA, for years while NASA founded CUBES in 2017 to study genetically-modified microorganisms as part of the LSS, with an eye towards food, therapeutic pharmaceuticals and bioplastics, with oxygen as a side-product.

The atmosphere, and the potential dust and soil and mould problems seem to be shoved to the side with, "We're working the food and waste problem! Hell with it, the ISS system is Good Enough, use that."

Personally, I think a partial open-loop system that recovers water, nitrogen and heat, bubbles the waste atmosphere through a supercritical water reactor to sterilise before venting, and takes in oxygen from the regolith electrolysis and/or CO2 electrolysis would also be Good Enough. Perhaps something like activated carbon could be produced from the left-over carbon, as it's used in an extruded form to filter noxious odours and chlorine.

Edited January 2 by AckSed

[farmerben]

I'm skeptical about lunar concrete.  It's water intensive and I don't know how that will work in a vacuum.

[Pthigrivi]

2 hours ago, farmerben said:

I'm skeptical about lunar concrete.  It's water intensive and I don't know how that will work in a vacuum.

Definitely. Im gonna try to stick to mars to reduce the variables but 100% water and cement production are huge hurdles. Concrete is great because it has huge compression strength and most of the aggregate mass can be easily produced locally. This is why I'd stick to pre-cast components that can be formed, poured, and cured in climate controlled workspaces. That way all of the water that evaporates during the curing process can be recovered and reused. They should be essentially dry before being installed. 

Thinking more about it though I've got a worse problem. I honestly think the skylights just aren't worth the rigmarole. Better to bury everything and use artificial skylights. Another thing is that on mars the regolith is all going to be at -60c and without a ton of insulation all of the interior surfaces are going to become cold moisture collectors. The funny thing is the air is so thin it's actually a great insulator but that's tough when you're buried under 2-3m of regolith. You kind of want your envelope to be cleanable interior > radiant heat panel > vapor barrier > insulation > air gap > concrete > regolith. Hard to do with minimal thermal bridging. 

There are some advantages though. Mars has a little over a 1/3 the gravity so I think that means you need about 1/3 the structure to support the same weight? 

Edited January 3 by Pthigrivi

[darthgently]

5 hours ago, Pthigrivi said:

m still struggling with is how to maintain comfortable humidity levels without the whole colony becoming stuffy and musty

Too true.  This is one reason why I’ve always thought that the long term solution is getting cheap cubic footage.  If you have enough room you can have entire biomes with a full cycles for water, air, food etc.  using AI to regulate homeostasis.  I imagine starting at the ISS level with a fully synthetic “biome” that we use now to a degree but slowly introduce scalable real biome modules that better mimic the systems we take for granted here.  Fungi, trees, soil, everything that complements our biology.  Big green habs.

[Pthigrivi]

Okay one more before bed. Ive done my best to (guesstimatedly) optimize building material for usable, climate controlled and radiation shielded space. I think the greenhouses don't need to be radiation shielded and could be on an automated conveyor system that reduces the amount of time human maintenance crew need to be exposed to high GCRs. It takes about 1 acre of cropland to feed 1 person, but let's say we can be REALLY efficient, packing mobile hydroponics 4 racks high, supplementing with LEDs for 24 hour growth, maybe, maybe, we can get greenhouse square footage down to 2500-3000sf/person. You're almost certainly going to need more area for crop growth than all habitable interior space combined, but if most hab spaces are 2 stories deep it might shake out. If we bury all of our habs and then build an endless greenhouse on top it just serves as an extra layer of thermal and radiation absorption. For the max hab module size I thought about the maximum volume any common social space would require. Since mars has very low gravity I think regular exercise will be really important to bone and muscle health, so I took the width of a basketball court with room for bleachers either side and then multiplied the record vertical jump (4'+) times 3, and added 8' for the tallest likely person on mars to make sure folks wouldn't bang their heads on the ceiling. 20' is convenient because its about 2 regular stories for non-athletic hab space. I think this is a plausible, relatively efficient urban crossection of a mars colony that has the ability to manufacture large quantities of concrete, steel, aluminum, rock-wool insulation, and plastics. Most of this space would be served by simulated LED skylights, but as in previous versions could be punctuated by elevated, cleverly shielded parks or boulevards that offer natural light and views of the horizon. 

Edited January 3 by Pthigrivi

[farmerben]

7 hours ago, Pthigrivi said:

Since mars has very low gravity I think regular exercise will be really important to bone and muscle health, so I took the width of a basketball court with room for bleachers either side and then multiplied the record vertical jump (4'+) times 3, and added 8' for the tallest likely person on mars to make sure folks wouldn't bang their heads on the ceiling. 20' is convenient because its about 2 regular stories for non-athletic hab space

In 1/3g you can jump 9 times higher.  In 1/6g you can jump 36 times higher.

[farmerben]

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

Quote

Lunar lava tubes may potentially serve as enclosures for human habitats.^[5][8][21] Tunnels larger than 300 metres (980 ft) in diameter may exist, lying under 40 metres (130 ft) or more of basalt, with a stable temperature of −20 °C (−4 °F)

You can start where lava tubes already exist.  Very interesting wiki page.  Some of the natural skylights are as small as 5m, quite easy to dome over.   The large 900m skylights would be quite difficult to dome over but not impossible.  

Edited January 3 by farmerben

[Pthigrivi]

7 hours ago, farmerben said:

In 1/3g you can jump 9 times higher.  In 1/6g you can jump 36 times higher.

Wait are you sure? Google says closer to 2.6x times as high?

[farmerben]

2 hours ago, Pthigrivi said:

Wait are you sure? Google says closer to 2.6x times as high?

Wait.  You're right the figures I quoted are for rockets where you convert most of the mass into propellant.  Jumping 6 times higher on the moon is correct.

[Pthigrivi]

Alright look I honestly think its best to bury almost everything. Clever enough with hydroponic conveyors but its just so many points of failure and the thermal insulation is going to block almost all of the sunlight anyway. It's, heavy, we're putting crops at the bottom and feeding it with LEDs run on nuclear. I keep coming up with about a 100-120' span, mainly because thats about as big a component I can justify precasting indoors and hauling to the site in one piece. Im liking this idea of a series of gantries on rails that deliver everything from the point of manufacture to the point of assembly. I think that will give the kind of efficient, precise assembly needed to keep the process moving quickly. 

[tater]

Someone needs to get cracking on gigawatt reactors for space applications.

[darthgently]

Was reading about zircon crystals on moon indicating it could be as old as the earth so asked grok what this might imply about fissionable materials and carbon at deeper layers of the moon:

Spoiler

Recent research has suggested that the Moon might be significantly older than previously thought, potentially as old as the Earth itself. Here's an overview of this evidence and its implications:

**Age of the Moon:**
- **Zircon Crystals:** New studies have found zircon crystals in lunar samples that indicate the Moon could be about 4.51 billion years old. This age aligns closely with the Earth's estimated age, challenging the theory that the Moon formed later from a giant impact event involving a Mars-sized body called Theia. This evidence suggests that both Earth and the Moon might have formed together, possibly as a binary system.[](https://www.nationalgeographic.com/science/article/moon-even-older-than-we-thought-lunar-formation)[](https://x.com/ExploreCosmos_/status/1869841677411553776)

**Implications for Fissionable Materials and Carbon:**

- **Fissionable Materials:**
  - **Nuclear Fission Hypothesis:** The fission hypothesis for the Moon's formation, although less popular than the giant impact theory, posits that the Moon could have formed from a nuclear explosion due to high concentrations of fissionable materials like uranium and thorium in the early Earth's core. If the Moon is indeed as old as Earth, this could imply that the materials from which the Moon formed were already present in significant quantities, potentially supporting a scenario where such materials were naturally concentrated through processes like differentiation or even natural nuclear fission reactors in the Moon's interior.[](https://www.sciencedirect.com/science/article/abs/pii/001910357890012X)
  - **Nuclear Power Exploration:** The presence of fissionable materials deep within the Moon could be relevant for future lunar missions, especially those considering nuclear power sources like Kilopower, which might use such materials for sustainable energy on the Moon.[](https://en.wikipedia.org/wiki/Lunar_resources)

- **Carbon:**
  - **Carbon Presence:** The Moon has traditionally been considered very poor in carbon compared to Earth. However, if the Moon is as old as Earth, it might imply that carbon was part of the early material from which the Moon formed. This could suggest that carbon might be found in deeper layers of the Moon, perhaps from an ancient magma ocean or from impacts that brought carbon-rich materials to the Moon. The presence of carbon in deeper layers could also influence our understanding of the Moon's geological evolution, including potential volcanic processes.[](https://en.wikipedia.org/wiki/Geology_of_the_Moon)
  - **Implications for Lunar Resources:** If carbon is indeed present in deeper layers, this could have implications for future lunar exploration and resource utilization, as carbon is crucial for various industrial processes, including the production of solar cells or as a component in life support systems.[](https://en.wikipedia.org/wiki/Lunar_resources)

In summary, if the Moon is as old as Earth, it suggests that the materials forming the Moon, including fissionable materials and carbon, were part of the solar system's early composition. This could lead to a reevaluation of the Moon's geological history, its resource potential, and the mechanisms by which it was formed. However, these implications are speculative and would require further exploration and sampling to confirm.

 

[tater]

BTW, @Pthigrivi, these designs (and underlying observations about concerns/requirements/etc) are extremely interesting stuff.

[Entropian]

On 12/20/2024 at 8:24 AM, farmerben said:

it should be possible to seal the air in with a very thin layer of vinyl

Very late to the party here, but vinyl won't work.  Most polymers have a very high porousness to air, and thus undergo an effect called "outgassing."  Air inside the chamber will slowly move through the vinyl into the rock fractures over time, but the more surface area you have, the faster it'll be.  Incidentally, this is one of the primary reasons that the highest-vacuum joints entirely avoid polymers; instead, they cut annealed copper to form a joint that doesn't outgas, unlike polymer O-ring seals.  If you're interested, you can look into "Conflat" and "KF" vacuum joints.

[StrandedonEarth]

4 hours ago, Entropian said:

Most polymers have a very high porousness to air, and thus undergo an effect called "outgassing."

What if they used butyl rubber, which is used for the airtight liner in tires?

[farmerben]

4 hours ago, Entropian said:

Very late to the party here, but vinyl won't work.  Most polymers have a very high porousness to air, and thus undergo an effect called "outgassing."  Air inside the chamber will slowly move through the vinyl into the rock fractures over time, but the more surface area you have, the faster it'll be.  Incidentally, this is one of the primary reasons that the highest-vacuum joints entirely avoid polymers; instead, they cut annealed copper to form a joint that doesn't outgas, unlike polymer O-ring seals.  If you're interested, you can look into "Conflat" and "KF" vacuum joints.

I'm afraid you will require a small maintenance replacement air program no matter what.  If you lose half your air to airlocks and active operations, and half your air to painted rocks that enclose a huge amount of space it would be worth it.  The air flow rate through solid basalt is not very great to begin with.  

I mentioned vinyl because I'm optimistic you could mix it in two parts and apply it via spray gun in a vacuum.  Polyethylene and Polyester are used more in food containers, i just don't know if they could be sprayed on.  Once you've got a chamber 99% sealed, you could probably simply pressurize it and use any water and air based paints similarly to how they are used on Earth.

Edited January 4 by farmerben

[Nuke]

i think a lavatube base would want reinforcement beyond simple pressure holding layers. because we have very little data about lunar cave collapse statistics. without weathering, i figure it would be better than earth, but the possibility of waking up crushed by a giant boulder is nonzero.

 

morlock problems i know.

Edited January 4 by Nuke