I've got a lunar colony that was set up to be self-sustaining before a collapse of life on Earth. The colony has survived on its own for several thousand years through a period of technological regression. But now they've recovered to roughly their original technology levels, and realize that they've been slowly losing something which will soon threaten their ongoing survival. What could a colony on the lunar surface slowly lose that would ultimately prove fatal?

Some notes on their technology:

• The colony is a shielded crater about 12km across.


• They have advanced, but not magical, 3D printing technology.


• They have large solar collectors for power, but no fusion.

Some thinking so far:

• The obvious answer is oxygen, but lunar regolith is 40% oxygen so that's easy to replace.


• My understanding is that lighter elements are more likely to escape even tightly-sealed systems via atomic diffusion or simpler processes like opening and closing airlocks. So a slow loss of hydrogen (rare in lunar regolith) seems likely, especially if there's a mechanism via which it would become unbonded from water.


• Humans need a lot of trace elements to survive (zinc, magnesium, iodine, etc). Is there some process via which a key one of these would be slowly lost, no matter how carefully things are recycled? (i.e. soil is tilled to recover, air is scrubbed, etc.)


• I know certain substances exposed to space for long periods of time will degrade or chemically alter (space weathering), possibly in ways that wouldn't be easy to reverse. For instance, the flags planted on the moon are supposedly bleached of color because of ~50 years exposure to UV rays. What substances are most susceptible to this kind of degradation? I have a notion that some of these processes might cause, say, atoms to bind together into molecules that can't easily be separated back into constituent elements, but haven't found good sources with more detail. But if so, the parts of the colony exposed to vacuum/space (solar wind/flares, cosmic rays, micrometeor bombardment etc.) might be a weak point.

Materials exposed to vacuum for extended periods often become brittle and/or literally lose mass over time.

Outgassing, cold-welding, decomposition of alloys back to their constituent materials, coronal arcing due to ionization from exposure to ionizing radiation, acceleration of outgassing and decomposition again due to ionizing radiation exposure are all concerns both for metallic elements, barriers and bearings, and outgassing particularly for all plastic, polymer or latex components (seals etc) induce changes in surface interface chemistry and surface finish, and over sufficient time these would impact significant portions of the volume of a material.

Further, scratches and dings in vacuum-exposed surfaces can lead to rapidly-propagating fissures and cracks, due to thermal expansion / contraction.

Bearings will cold-weld, and even failing that, lubricants which survive well in vacuum-whetted conditions are both rare and exotic, and many of the ones which are found to work cannot take direct insolation as they will themselves offgas and change composition. Think airlocks, manipulator arms or waldoes, locking / docking clamps, wheels, rovers, et al.

All these issues can of course be dealt with individually, but en masse it means that absent new metallic components along all vacuum-exposed surfaces, they will be in serious trouble. I don't know if your thousands of years is even feasible... NASA has been studying these material science issues since the 1960's, as you can imagine, and they've a lot to say about it.

Two other issues are sublimation of solid materials as temperature climbs during insolation, and corrosion, which can be very strange and unexpected when surfaces are impacted by ATOX (see ESA paper below) - all of which support my basic contention:

Material thermal stress / embrittlement / volume & mass loss / corrosion on all vacuum exposed surface materials are the single greatest threat / risk to a longstanding Moon colony, and absent re-supply / repair would constitute a rapidly self-reinforcing series of chain-reactions leading to catastrophic enclosure failures.

1961 JPL Paper on Vacuum Exposed Materials
1969 NASA Paper on Vacuum Exposed Materials
European Space Agency Paper on Corrosion in Vacuum at LEO

Hope that helps some.

Volatiles like hydrogen, carbon, nitrogen, and noble gases. These elements are necessary for life and useful for industrial processes, while being difficult to replenish. Hydrogen, carbon, and even nitrogen can be used as rocket propellant which will consume these elements without any chance of recycling. They are also liable to loss through slow leakage. It is difficult to replenish these elements because they exist at parts per million concentrations in lunar regolith. This means many tons of regolith must be processed to obtain small quantities. However, we do know that permanently shadowed craters at the lunar poles at least contain water ice. It's quite possible they can contain other volatiles too. These volatiles are probably much easier to extract than the volatiles adsorped into lunar regolith. But it's quite possible that with 1000 years of continued exploitation that these deposits could run dry. It's been estimated that the Moon's north pole could have 600 million metric tons of water ice. While this seems like a lot of water, consider that we produced about 380 million metric tons of plastic in 2018. It's quite possible that with heavy extraction, these deposits could be depleted much faster than 1000 years.

A non-obvious loss area would be Genetic diversity. After several thousand years of carefully controlled plant growth, and several thousand years of inbreeding, unless care was taken to maintain genetic diversity in plants and animals (including humans), a single mutated bacteria could take out a key component of the self sustaining ecosystem.

Immunity to Disease

Your lunar citizens live in a perfect environment! They have all the food they need, they have recycling that, frankly, removes most bacteria from their lives. Atmosphere is constantly recycled, which includes scrubbing. Water, too, is recycled, scrubbed and clean for use.

In fact, the colony has been disease-free for, well... forever.

And that is a massive risk. Disease has this nasty habit of hanging around. Stuck in some quiet, little corner of life or living until somebody moves the proverbial old stack of books in the attic out of the way and boom! you're sick.

And then everybody's sick

It isn't like everybody needs to start dying. Oh, they could. Diseases like polio, measles, etc., really aren't gone. We've simply enhanced human immunity through vaccination such that they can't get a foothold on the population anymore. If one of them peeked into the clean and controlled world of your lunar colony, it could wipe out the colony overnight.

But it really doesn't need to be that dramatic. Maybe it's just a newly mutated form of the flu. And suddenly people are having trouble getting out of bed, which means they're not maintaining and operating the closed, controlled environment. Repairs and adjustments aren't being made. And things begin to slip.

The funny thing is that doctors would be trying to fix the problem. At first it would be, "oh, this is an historical curiosity! When's the last time this happened? Here's two aspirin, you'll be all right!" Until one of them notices the problem. "Uh, Frank? You might want to take a look at this...." And then the medical community realizes the ugly truth, "uh, how are we going to stop this?"

Right up until Louise, who has an absolute genius for maintaining the ventilation systems, can't make it to work.

And then a fuse buried deep in the ventilation system blows....

And with his last breath, Louise's apprentice, who'd been buried in technical manuals and user guides for a week, says... "I think I fou...."

It's not about what gets out, but what gets in. To survive that long, mankind will make many many trips out into the Lunar landscape to gather and process lunar regolith so that they can replace lost air and water supplies. However, regolith is extremely hazardous to human life. It's highly abrasive, nearly impossible to filter, and it builds up in the lungs causing Silicosis. Each time a lunar rover goes out to get more of the stuff, a little bit more of this fine dust comes in on the vehicle's chassis. Slowly it's concentrations build up in the air of the colony increasing the cases of respiratory ailments and early death until eventually, it kills so fast that no one can survive long enough to procreate.

Genetic Diversity

With the relatively small breeding population, over tens or hundreds of generations minor genetic defects could be interbred into major genetic defects. It's up to the author to determine what kinds of defects are being introduced. Based on those choices, the colony may be in danger of dying out from a single bad virus or defect induced infertility that forces birthrates too low to sustain the colony.

The will to live

Survival on a lunar colony is a lot harder than here on planet earth. You are tired at the end-of-day, and the time to have and raise kids is just a little more than you can take. Population decreases until there is just not enough left for the colony to be viable/

Something we didn't know we needed, because we always had it.

The people who built this colony were not fools. They would know plants need boron and humans need sodium. There would be provisions to tap lunar water and generate building materials and oxygen from regolith. Carbon is precious and would be carefully conserved. There will not be holes in the recycling scheme.

Likewise genetic diversity. The builders know about inbreeding. They know that charged particles hitting the moon can cause mutations. There would be giant sperm and egg banks for diversity and molecular genetic remediations.

But what about something humans have always had and so never missed. Something that keeps humans going, but is slowly dying. And when it is gone, we will slowly die as well. I mean Gaia - the Earth.

Maybe the gestalt of all that is alive on Earth is tied to life in some way - something that has been there so long that there is no name for it. And Gaia is not going to go easy. After the humans escape the Earth there is still life; the deep things, the tenacious things. Roaches and mites, the bacteria, the fungi. And maybe this power is great enough to reach the moon - so the humans there and their dogs and corn are sustained even though they do not know that they are.

But if there is a tipping point, and after thousands of years the last feeble weed finally dies, whatever this power is goes with it.

It would be a sad story.