Fast Company
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Life on the moon could be a possibility as it may have enough frozen water to support a future human settlement! But not enough for a sprawling lunar city.
The moon may have enough power for massive cities. There’s just one problem
Author: Taylor Hatmaker
There’s a sea of ice lurking on the dark side of the moon, but even that may not be enough to quench the thirst of a future lunar colony.
Moon colonies have long been fodder for science fiction, but governments and private companies are racing now to make those extraplanetary dreams a reality. The main catch? Like the plot of every good hard sci-fi tale of humans in space, success hinges on the day-to-day drudgery of resource management.
On the moon, water is that vital resource, made all the more important by its local scarcity. NASA describes the moon as “100 times drier than the Sahara,” but the confirmation of frozen water in the moon’s permanently shadowed areas raised hopes that explorers could tap into the stores for future lunar colonization.
Those secret stashes of ice will be essential to any human activity on the moon, but experts say that the frozen liquid isn’t enough to build proper moon metropolises—not yet, anyway. In a research paper published in the journal Frontiers in Space Technologies, Martin Elvis, an astronomer at the Smithsonian Astrophysical Observatory, and Jonathan McDowell, a space sustainability analyst, explored just how much it would take for a large-scale human civilization on the moon to succeed.
Water, water everywhere
The researchers ran their analysis using a “generous baseline” of 1 billion tons of water, rounding way up on current estimates of the moon’s frozen water stores. That volume of water—“enormously more” than was known on the moon before 2013, the research points out—could fill an area the size of Manhattan’s Central Park to a depth far taller than the Statue of Liberty. But how far could that amount of water take the human race?
Any human settlement on the moon will have a massive requirement for fresh water. “Water usage for a lunar city will come from several needs: personal usage for drinking and hygiene, growing food, rocket fuel and, unlike on Earth, breathing,” the researchers wrote. “All these human activities will necessarily take place in a built environment, given the lack of any substantial atmosphere” on the moon.
Some of that water can be recycled using current technologies, but not all of it. Until 2023, the water recycling system of the International Space Station (ISS) was capable of repurposing 94% of the volume that flowed through it. “At that efficiency a billion tons of water is gone in 40 years for a population of 1 million,” the researchers observed.
After 2023, the ISS system’s efficiency improved to recycle 98% of water thanks to something called a brine processor assembly that wrings more water out of the ultrasalty brine from urine. That system would buy moon colonists working with a billion tons of water 100 years to run dry, but there are caveats.
Limits of a lunar city
A future moon colony won’t be as efficient as the ISS, given long-term needs like laundry, showers, and toilets designed for the moon’s gravity, about a sixth of the Earth’s. While astronauts tolerate a lack of amenities on the ISS during their six-month stints, a moon colony needs to support humans for the long haul.
“For such a large investment, a lifetime of about a century seems to fall short of the sustainable, long-term settlement beyond Earth that some advocate,” the astronomers wrote. “A small city of 100,000 people will instead take 1,000 years [to] use up all the water.”
While a city of 1 million people would run through its water relatively quickly, bringing the scale of a lunar civilization from the size of say, Austin, to something closer to Albany, New York, would make the numbers much more favorable to long-term colonization. “Water seems to impose a limit of a few hundred thousand on the long-term lunar population,” the researchers wrote.
There are ways around the hard cap. The most obvious is that water recycling technology could make another leap in the future, but the researchers caution that the necessary improvement over current systems would be “hard to reach and to maintain, even for a disciplined and motivated population.” For a city of 1 million people to sustain itself for 1,000 years on an already generous estimate of the moon’s water stores, water recycling advancements would need to be 10 times as efficient as the ISS system.
Other techniques like vertical farming and a low- or no-meat diet could slash water needs substantially. Water could also be shipped to a lunar colony from elsewhere, though that solution would depend on a massive shipping operation and nearby asteroids rich in frozen water. The last solution—the moonshot, if you will—is of course finding an undiscovered well of water on the moon itself.
Ultimately, any hope for a future moon city will necessitate plenty of planning and thoughtful stewardship of the lunar ice that we do know about. “Humanity will need to plan, govern and regulate the use of lunar water, rather than adopt a ‘first come first served,’ free-for-all approach to water extraction and use,” the researchers wrote. “If the lunar population is to grow beyond a hundred thousand, water management will be critical and challenging, and we should evaluate the options well in advance.”
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