Homesteads are primarily sub-surface

The Lunar surface is hazardous and challenging. It’s one of the reasons why we don’t have lots of robots on Luna doing all kinds of cool things (mining, building habitats, exploring, etc.). It’s very difficult to design and build machines that can operate for long under those conditions. The same goes for structures.

Lunar surface hazards

Here’s the short list of Lunar surface hazards. It’s not comprehensive. I wrote a small post on Lunar Surface Mining Challenges (lunarhomestead.com/2018/08/01/lunar-surface-mining-challenges/) but it all applies to any surface activity. I’m also making Lunar Frontier Challenges (which will include all the surface hazards) the second book of this series. Check out the LH website for a lot more information.

  • Lunar dust – This isn’t just any dust. First, it’s super small; the average size is 70 µm [90]. The human eye can’t even see things below 40 µm [91]. Some of it is so small that it can get deep into your lungs and enter your blood stream. This can cause all kinds of chronic, and fatal, diseases. The dust also gets into all moving parts (joints, gears, axles, etc.) and quickly destroys them. See, the dust isn’t just small. It’s also extremely jagged and sharp. It acts like an excellent abrasive. Finally, the dust is very clingy and gets everywhere (it killed an Apollo 11 seismometer by overheating it). Keeping it off machines and out of habitable areas is going to be a huge challenge.
  • Radiation – I talked about radiation a bit already. Anything on the Lunar surface is constantly exposed to high levels of radiation. During nightspan Galactic Cosmic Radiation (GCR) (high energy particles originating from outside the Solar system) is coming in from all angles not blocked by Luna itself. During dayspan, Homesteaders have to deal with GCR and Solar radiation (especially coronal mass ejections). Enough radiation can destroy both equipment and people.
  • Vacuum – Obviously, we must have some kind of pressure hull (or suit) to survive in a vacuum. Actually, Luna does have a very thin atmosphere but it’s close enough to vacuum to ignore it. We have to make sure nothing compromises the integrity of our hull (see impactor below). Vacuum is also hard on machines as well and it takes a lot of engineering to make them work on the Lunar surface.
  • Impactors – The Lunar surface is defined by meteoroid impacts. Just look at all the craters. The big hits don’t happen all that often. However, smaller impacts occur more often. The odds of a habitat being hit by something big and fast enough to puncture it are pretty low. But it’s not zero.
  • Temperature extremes – Temperatures can swing between 123º C (during dayspan) and -233º C (nightspan) [92]. And they can last for a long time because dayspan and nightspan last 14 days each. This isn’t good for unprotected electronics, machinery, and structures. Not only does the temperature cause damage but the cycling from hot to cold to hot can induce failure as well.

Current paradigm

The conventional approach to protect humans and equipment is to bury the habitats under meters of regolith. You can see drawings of this in most of the literature and plans. It sounds simple at first glance. Put the structure into position and bulldoze the surrounding regolith over it. Voilà, instant shield. Unfortunately, there are several substantial problems with this technique.

Dust, dust, dust! Seriously, Lunar regolith dust is no joke. We still don’t fully understand all its properties and risks. We also don’t have fully developed and effective mitigation tech. Sure, there’s lots of ideas and drawings but few working examples. What do you think is going to happen when we start pushing regolith around with bulldozers? It’s going to kick up a lot of dust, of course! It’s easy to imagine a huge cloud of dangerous dust engulfing the habitat and mining site. Even worse, there are designs that use a supersized snow blower to move the regolith. I can’t imagine a more effective way to cover everything in dangerous Lunar dust. And this dust cloud isn’t going away quickly since Luna has effectively no atmosphere and a mild gravity. Honestly, we don’t really know what will happen when we start conducting large scale regolith moving operations.

There are numerous other problems with covering the habitat with regolith. Here’s just a couple. One, Lunar regolith dumped in a 10-meter pile will naturally come to a 40-degree angle [93]. This isn’t very high when we factor in the height of the habitat and the needed thickness of the regolith shielding. Some sources claim 4 meters of regolith is enough [94]. I’d want more if I was a Homesteader.

Let’s say our habitat is 6 meters in diameter. Add in 4 meters of regolith and you’re set, right? Nope. Now you have to figure out the geometry of the shielding because we need to have 4 meters of regolith covering every square centimeter of the habitat. Thin spots are a hazard to the crew. Now you have to play around with adding awnings, making the pile higher and wider, or adding in a regolith containment system. All of this adds a lot more material, equipment, effort, and time.

Two, mechanical compaction with equipment can’t replicate the density of in-situ Lunar regolith [95]. Higher density means greater radiation and impact protection. Even if we wanted to complicate things further by adding equipment to compact the regolith shield once it’s in place; it still wouldn’t be as good as just leaving it alone and tunneling underneath it.

Third, you’re putting a highly abrasive substance that’s known to get into everything directly on the habitat hull. In my mind, that’s just asking for trouble (especially if the habitat is inflatable). Plus, how is the crew supposed to do maintenance or repairs to the hull with loose regolith on top of it? A few plans call for using sandbagged instead of loose regolith. But now you have to either import or manufacture bags. And then you have to fill them, seal them, and place them over the habitat in specific spots. That’s even more materials, equipment, effort, and time. Plus, you either need specialized (and expensive) robots or humans out there on the surface placing the sandbags (because it’s not as simple as spraying regolith). We’ve already touched on how hazardous Lunar surface operations are.

What about lava tubes? Lunar lava tubes are all the rage these days even though their existence is still theoretical. We’ve seen images of holes that look like they could be “skylights” into lava tubes but that’s it.  The thought is that lava tubes will provide a natural shelter where we can build bases and settlements. Sounds great but we still have to actually find and explore one first.

Other designs have us constructing a dome over a crater, filling it with breathing gas, and then building a city inside. Some of them even have two domes with water in between so natural light can get through. These designs sure do look inspirational even if they aren’t realistic. The amount of science and engineering research we would have to do before attempting this is staggering. The Lunar industrial base needed to support such an effort would have to be both wide and deep. Maybe a mature Lunar civilization would attempt to make a crater habitable but that’s so far into the future that it’s all speculation at this point.

Lunar Homestead paradigm

Lunar Homestead mitigates or eliminates those hazards by building almost everything under the regolith. The goal is to disturb the regolith (and its dangerous dust) as little as possible. The project I’m currently working on is SPORE (Shielded Pressurized Oxygen Resource Extraction). SPORE combines resource extraction (aka mining) with habitable space construction by skipping the regolith and going directly to the mega-regolith.

  • Shielded – The Pathfinders will dig a vertical shaft through the regolith to a depth of at least 10 meters. That should get them under the large majority of the dangerous small particles (particle size is thought to increase with depth). Then they will create the Homestead under that layer of regolith. The Homestead will automatically be protected from radiation, thermal extremes, and small impactors. The mega-regolith they excavate should consist of very little of the dangerous dust (although we really don’t know for sure). Even the vacuum might be less of an issue with enough regolith and mega-regolith overhead. I plan on running a few experiments on that. See the website for more information.
  • Pressurized Oxygen – Designing equipment to operate in vacuum is difficult and expensive. And obviously, humans have to wear protection if they want to get stuff done. So, the solution is to partially pressurize the work environment and be done with the vacuum altogether. Basalt refining operations is going to generate a lot of oxygen, probably more than the Homestead can use or store. Pressurizing the work environment with pure oxygen eliminates a bunch of challenges without adding too many. The fire risk can be eliminated by keeping the pressure low and eliminating fuel sources.
  • Resource Extraction – SPORE is primarily a mining technique. However, the side benefit is that space is created as material is extracted. Homesteaders can then build a pressure hull in that space. Fill that hull with breathing gas and you have a habitable space. Sure, it needs more bells and whistles to become a Homestead but it’s the crucial first step.

In the next section I’ll talk about why we’re going to put as much as possible into the Homestead’s habitable space instead of leaving most of it on the surface. Here’s a hint: the surface is dangerous and difficult.

One final thought about building settlements underground. Surface transportation suffers from all of the above problems but worse. Why worse? Because surface vehicles will be more vulnerable (less protection, moving parts, etc.) to breakdown and travelers won’t have to be very far from home for a breakdown to be fatal. Lunar surface travel is a high-risk activity. Apollo got away with flimsy open rovers through guts, luck, and very short stays.

The logical solution is to connect Homesteads, towns, bases, and outposts with underground roads. Simply build SPORE pressure hulls in the direction you want to go. Avoid dust, radiation, and lots of surface obstacles. Sure, it will take longer and involve a lot more work. The result will be a lot more lasting however. It wouldn’t even have to stay pressurized.

Ultimately, I envision a vast network of underground settlements linked by underground roads. One of my favorite fiction settings is the Deep Roads from the Dragon Age video game; linking Dwarven thaigs (settlements) and mines together. Or Khazad-dûm for those familiar with the Lord of the Rings franchise. The surface is dangerous. Underground is where the true action lies.

Resources

93) Lunar Source book (pg. 523)

94) https://space.nss.org/settlement/nasa/spaceresvol4/human.html

95) Lunar Sourcebook (pg. 521)

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