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No one has figured out safeguards against solar radiation. NASA does not permit any astronauts to live on the International Space Station for more than a year and the ISS is shielded by Earth’s Van Allen Belts which our moon does not have. Whoever lives on the moon will be exposed to elevated levels of radiation and develop irreversible cancer or radiation poisoning as a result until the fundamental problem is solved.

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To be specific: the exposure during a day of lunar living would be equivalent to ~2.6 days on the ISS, or ~200 days on Earth's surface[1]. And that's the normal dose, before we even begin to worry about solar events.

[1]: https://www.science.org/doi/10.1126/sciadv.aaz1334

> To be specific: the exposure during a day of lunar living would be equivalent to ~2.6 days on the ISS, or ~200 days on Earth's surface

If we do nothing to shield occupants.

Yep, shielding will be critical. The paper linked above has this interesting note:

> Settlements on the Moon will provide additional shielding because they will be buried beneath layers of lunar regolith. While this would decrease the dose rate from charged particles, the absolute contribution from neutrons is expected to increase for shielding constructed from in situ resources, as borne out by measurements with the Apollo 17 Lunar Neutron Probe Experiment. These showed that the flux of thermal and epithermal neutrons increases significantly up to a depth of approximately 150 g/cm2 (31).

So plans to shield lunar occupants using the moon's own materials will need to compensate for the ionizing radiation that those materials are already emitting, separately from cosmic/solar radiation.

> So plans to shield lunar occupants using the moon's own materials will need to compensate for the ionizing radiation that those materials are already emitting, separately from cosmic/solar radiation.

It's not really that they're emitting them "separately" -- they're radioactive (with mostly short half lives) largely because of solar bombardment. Thin shielding can paradoxically make things worse by converting high energy protons into more, lower energy neutrons.

If your shielding is thick, the inner layers will rapidly become less radioactive (the important half lives are less than 30 days). The outer layers will keep getting hit by solar protons and creating more unstable elements.

Another major concern in the long term: radon gas. One had better have an inner hull and never rely upon sintered regolith to hold atmosphere.

>~200 days on Earth's surface

Where? there is a big difference between Miami, Colorado, Guarapari, and finally Ramsar

Here's the calculation based on the NRCP's 2009 estimates for the US[1]: the average US inhabitant is exposed to 3.11 mSv/year, or 3110 uSv/year. That's an average of 8.52 uSv/day, compared to 1369 uSv/day on the Lunar surface.

For the US, that's a factor of ~155x, not the ~200x that I saw in popular media, so I'm not sure where they got the latter from. But "over 150 times the daily exposure of the average American" isn't fantastic.

Edit: https://en.wikipedia.org/wiki/Background_radiation#Backgroun... has other numbers for "background only" exposure in various parts of the world. The US seems to be among the higher areas for latent exposure, so it's probably safe to say that the 155x number is on the lower side of things.

[1]: https://www.cdc.gov/nceh/radiation/cosmic.html

so we are talking ~5x Ramsar https://pubmed.ncbi.nlm.nih.gov/11769138/ where people live normal lives

n=35 for that particular study[1], which notes that results are preliminary and doesn't include any prescriptive language like "normal lives."

The theory they advance is the people of Ramsar are demonstrating an adaptive response to large amounts of background radiation. But there's no evidence (or even theorization) that said adaptive response extends to fully mature adults.

[1]: https://sci-hub.se/10.1097/00004032-200201000-00011

The ISS doesn't have a moon to bury itself inside.

You only have to go 2.5 meters down to provide the same level of protection as being on the surface of the earth.

Sounds good… do we still get to have skylights?

edit: I’m genuinely curious if it’s possible to allow sunlight while blocking harmful radiation, our atmosphere does it, can a thick window do the job?

If you want to live above ground and have other niceties then there's a great planet that's really close to the moon.

Yes, but if all humans are on that one, then if there's a catastrophic problem there: Houston, we have a problem.

Not one that’s likely to be solved by spreading to the moon. Personally I have much the same attitude about the eradication of the human race as I do about dying: it’s going to happen eventually, best to make out time here as good as possible rather than trying to extend it indefinitely at all costs. And giving up the earth seems like a huge cost to me.

Water blocks radiation, too. Keep the water supply in clear tanks above the base in spots.

You can put in a skylight if you really want to, but a lunar day is 708 hours long.

Simulated skylights are probably possible, but you may have to go a bit deeper to create the space for an effective simulation.

Mirrors, or even artificial sky lights are a thing.

Probably by delivering sunlight through a fiber.

Lunar lava tubes.

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

I envision that and them some sort of inflatable shell insterted into it to make a quick habitat... maybe some sort of hardener is activated upon inflation or filled in between outer layers...

Yeah, lunar real estate will be one of the first things - Location. Location. Location.

That’s why you build in a lava tube, a permanently shadowed crater (bonus: ice!), or cover the base in regolith.

3d printed buildings. I'm not even kidding. I've been soft-offered a job to write software for this that might get deployed to space. I am seriously thinking about taking the job and using it to get into the astronaut program. It would be pretty badass to be the first person to build a permanent structure off the planet

DO IT! That sounds so cool!

Also is it possible to maintain muscle mass in space for over a year? What happens when you lose the bone density. Or could this been circumvented with a couple of hours of squats every day and other exercises using bands as resistance

Muscle loss isn't too bad. The real killer is bone loss. You lose 1% of your bone mass per month in space. NASA still hasn't figured out how to fix it. Valeri Polyakov spent 437 days on Mir in 1995. Nobody has come close to that record since then, and nobody will until the problem is fixed.

And no one knows how much gravity you need to fix this. That's one reason a moon base would be beneficial.

Does 16% gravity let you do exercises that let you keep most bone density? Is it pretty much the same as microgravity? Or is it somewhere between-- just slightly less bad than orbit.

I have some hope that 16% + an aggressive exercise program could be OK.

As someone currently learning how to lift weights, I would love to be the guinea pig of a lunar exercise program.

At 16% gravity I should be able to deadlift over 1500 lbs and bench 1000 lbs!

I bet having 6 times as much inertia for the weight makes things strange.

In all seriousness, it's going to be mostly resistance exercises. But we can probably do better resistance exercises with gravity to help posture and alignment.

The Moon at least has 0.16g, which is a lot better than 0g.

The powerlifter in me hopes mooners will just be deadlifting 1000+ kilos for reps to stay in ship.

Interesting - I wonder if it would feel different, with conservation of momentum being a bigger portion of the effort than gravity vs. on Earth.

What I mean is it would be something between lifting 100kg and pushing a car in neutral and stopping it.

I suppose the force curve might resemble that of reverse band lift?

Wonder if it's a matter of slapping on some bands to make it feel "earthy" or need mechanism like vacuum tubes they use in the ISS gym (Advanced Resistive Exercise Device). From what I read, it simulates the 1G lifting pretty close.

Spin the spacecraft. Done.

It works in principle, but it's a very big engineering task, and an enormous expense to boot. To avoid noticeably different acceleration between head and foot,* it's going to have to be substantially larger than any spacecraft we've ever built, and the biggest spacecraft we've ever built cost over $100bn. It's also going to have to withstand stresses larger than anything we've done before.

There's no reason to doubt we could do it, but it's a very big step from where we are now.

* And if we don't do that, then we stray into the realm of untested biological issues. We have no idea if people can live safely and comfortably like that.

Spinning a spacecraff is mostly hard because of the mass constraints, building a banked circular track on the moon should be much easier.

It is literally two things connected by a rope. A tether-based spun spacecraft is trivial from an engineering perspective, and can have as large a radius as you need to avoid differential “gravity” effects.

Off the top of my head:

- What material are you making the rope out of? What data do we have of that material's behaviour under tension in a vacuum?

- How is the craft connected to the rope? Is it a fixed bond or is there freedom to move? What are the tradeoffs?

- What happens when one of the two ends is accelerated? How do you reestablish a stable rotation?

- How do you manoeuvre it? Can you?

- What happens in the event of a catastrophic failure of the rope? What safeguards need to be in place?

And this is all on top of the fact that we're discussing two things connected by a rope under conditions that rope has never been tested in, doing something that's never been done. Space exploration isn't in the habit of trusting that our untested models are reliable, especially where human life is involved.

It is unknown if it will be that easy. For obvious reasons, there have been no long-term studies in partial gravity. If 0.05g stops bone loss, great. If a full 1.0g and nothing less is required, then that's going to be a really onerous design constraint.

I wonder if this unknown may, in the end, turn out to be a great reason to motivate space exploration. A full G is the norm on Earth. Micro-G in orbital stations have known long-term negative effects on health. What if fractional-G actually has beneficial effects, like say, increasing average human lifespan a lot. The human circulatory system tends to fail early, causing a disproportional amount of deaths due to strokes or heart failure. It's far-fetched speculation on my part, but is not hard to imagine operating in a fractional-G environment could decrease wear and tear here, acting as a sort of medical treatment. In the end, people would have a great motivation for leaving Earth. Just dodging death, the ultimate enemy of all living things.

If a full 1.0g is required, that also makes it a much more difficult challenge on the moon. Spinning a module of a space station in zero g is one thing... trying to get a portion of a moon lab at 0.16g to 1.0g is a different challenge.

The advantage I see on the moon is that you have local mass to use. Yoy can build a large, banked circular track underground ground and then add cars as you expand.

Uh, if human habitation on the Moon requires living inside a centrifuge, then there won't be a human colony.

It depends on how much gravity is needed for how much time to stave off the long term effects of zero gravity. If we're lucky, then just sleeping at a higher G may be enough and you just need the bunks built in a centrifugal train.

I’m always leery of solutions to complex problems that take the tone of “all you’ve got to do is…”

“There is a solution to every problem: simple, quick, and wrong.”

Lava tubes could help a lot.

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