Preface. There are so many difficulties to overcome to colonize Mars. If the astronauts can even survive the bombardment of radiation on the way there.

Where would the energy come from? There is no flowing water for hydropower. Wind and solar have many issues, let alone the cost of flying them there or building them on mars with new factories powered by? There are some hopium proposals for Martian wind power, but to make use of the ultra thin atmosphere the turbines would have to be huge. Geothermal energy, where heat is drawn from deep underground, won’t work on the geologically quiet Moon. It might work on Mars, but would be another enormous on-site construction project, and the best locations for geothermal power may not be the best locations for an early Mars habitat. Solar won’t work because space dust will clog the panels. Nuclear power may explode in a giant Ka-Boom!

The solar and galactic radiation that washes over Mars, which at its closest is 34 million miles away from Earth, is potentially 700 times as great as what passes through our magnetic defenses (Tingley K (2023) The bodily indignities of the space life. New York times. https://www.nytimes.com/2023/11/12/magazine/space-living.html).  If you don’t want to read a whole book, this article has a good summary of the many reasons why other planets and outer space can harm or kill you in dozens of ways.

Asteroids and other planets are not made out of platinum, lithium, and other valuable minerals. There is zero economic incentive to go into space.

Basically the book makes the case that even if climate change ravaged the planet with heat, drought, and more, if a nuclear war caused a nuclear winter for a decade, and so on — the Earth would still be a better place to be than Mars or the Moon.  I discuss other obstacles at energyskeptic.com in post:

If this topic interests you, I highly recommend Mary Roach’s “Packing for Mars”, which was very funny. So is this book. Also my post “Escape to Mars after we’ve trashed the Earth?”.

At any rate, renewable EV, wind, solar and so on use 6 times more metals than fossil equivalents, and will require orders of magnitude more mining to get them. We are already razing (rain)forests for cattle ranches, oil palm, and soy plantations. Climate change heat and drought are turning vast areas into deserts. Seems to me like there is no need to go to Mars, we are transforming our planet into another Mars.

Alice Friedemann  www.energyskeptic.com  Author of Life After Fossil Fuels: A Reality Check on Alternative Energy; When Trucks Stop Running: Energy and the Future of Transportation”, Barriers to Making Algal Biofuels, & “Crunch! Whole Grain Artisan Chips and Crackers”.  Women in ecology  Podcasts: WGBH, Financial Sense, Jore, Planet: Critical, Crazy Town, Collapse Chronicles, Derrick Jensen, Practical Prepping, Kunstler 253 &278, Peak Prosperity,  Index of best energyskeptic posts

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Weinersmith K (2023) A City on Mars: Can we settle space, should we settle space, and have we really thought this through? Penguin Press.

The average surface temperature is about -60°C. There’s no breathable air, but there are planetwide dust storms and a layer of toxic dust on the ground. Leaving a 2°C warmer Earth for Mars would be like leaving a messy room so you can live in a toxic waste dump.

On both the moon and Mars the shielding of choice in space will be dirt. The toxic jagged clingy dirt will blanket your habitat, perhaps as thick as a few meters to thwart meteorites, radiation, and temperature fluctuations while maintaining internal pressure.  Astronauts could bury themselves under the dirt. The downside is that rocket landings and dust storms might knock theshields off. More involved proposals call for sandbagging the regolith, baking it into a solid, or bonding it into bricks. If you can successfully bury everything in regolith, you now have to figure out how to keep humans from breathing it. Experience on the Moon suggests it will be a serious danger for health and for equipment.

Moon dust

The Moon isn’t just a sort of gray Sahara without air. Its surface is made of jagged, electrically charged microscopic glass and stone, which clings to pressure suits and landing vehicles. Nor is Mars just an off-world Death Valley—its soil is laden with toxic chemicals, and its thin carbonic atmosphere whips up worldwide dust storms that blot out the Sun for weeks at a time. And those are the good places to land.

So, that dirt you’re baking your three kilograms of water out of? It’s not exactly easy to work with. Harrison Schmitt of Apollo 17 reported allergy-like symptoms arising from inhaled moondust. Some habitat researchers fear that too much inhaled regolith over a long enough period will result in something like silicosis (also known as stone-grinder’s disease), in which repeated microscopic lung scarification makes breathing extremely difficult.

It’s not good for the equipment either. As John Young said during Apollo 16: “Houston, this dust is just like an abrasive. Any time you rub something, you can no longer read it. And that’s what’s happened to our RCUs and our . . . (pause) every piece of gear we’ve got. In other words, it’s a mistake to rub something to clean it off.

Regolith is a constant nuisance that shouldn’t be underestimated. The lunar surface is electrically charged, meaning it clings like fresh laundry. This is directly bad for machinery, but it also causes temperature dysregulation. Everyone knows black is the most awesome color for a space suit, but you never see one because white is the color that reflects sunlight. This is important because sunbeams reach the lunar surface without the mitigating influence of air. But the static cling of regolith means suits that don’t get cleaned slowly take on the dark plastery gray color of the Moon, making them absorb more heat. Once the coating is thick enough, it can also act as an insulator, which can cause a totally new problem—equipment that needs to radiate heat from human bodies cannot. Humans haven’t been on the Moon long enough for this sort of thing to be a big problem,

Robots have had it worse. It’s thought that the Soviet lunar rover Lunokhod 2 (“Moonwalker 2”) eventually died after it acquired a heat-retaining patina of regolith, ultimately cooking until it couldn’t function.

Martian Dust

Martian dust is more active than moondust. In 1971, as the first Mars orbiter, Mariner 9, approached its target planet, something happened that surprised the scientists. The red surface of Mars seemed to resolve itself into featureless smoothness—apparently a flat disk where a sphere was supposed to be. It turned out the entire planet, except for bits at the poles and the tall volcanic peaks, was enveloped in a single massive dust storm.

Impressively, from the perspective of human discomfort, these dust storms occur even though the atmosphere is quite thin—just about 1 percent of Earth pressure, almost entirely made of carbon dioxide. The net result here is that if you step outside, you still die about as quickly as you would on the Moon, but also from time to time the sky is blotted out by killer toxic dirt.

This will keep the humans indoors. Unfortunately, their outdoor equipment, such as solar panels, will become less useful when coated with toxic regolith. Even without dust storms, photovoltaics won’t work as well on Mars as they do in the equivalent latitude on Earth.

A digression to the TV show “For All Mankind”

Astronaut Garrett Reisman and planetary scientist Tanya Harrison discussed why Martian dust is a major impediment to colonization. As fine as talcum powder, it can stay in the air for weeks after a storm, and it’s got a static cling. It will coat solar panels, clog air filters and render ball bearings useless. It can cause lung disease in the astronauts and many other problems.  The astronauts would need to live three to four meters below the surface to be protected from radiation.  And may lose their eyesight, get heart disease and have other problems based on the much shorter timespans astronauts have spent in space.

Food cannot be grown without phosphorus, potassium, and nitrogen – the soils of the Moon and Mars don’t have these elements.

Back to the book

Given the limited public knowledge of space science in general, knowledge of its weird little cousin—space-settlement science—is almost nonexistent. And that’s where we arrive at the second problem. If you are ignorant about space settlement and want to become educated, many of the articles you’ll read, many of the documentaries you’ll watch, and pretty much every single book on the topic have been created by an advocate for space settlement.

Mars is easily the most inviting place for space settlement. The runner-up is the Moon, which among its many shortcomings is very poor in carbon, the basic building block of life.  The result of the general awfulness of space is that you’re likely living underground to keep the environment from touching you. Survival for a million people will require a very good seal-in, enormous amounts of electricity, an insanely large structure, and hardest of all, an artificial ecosystem to sustain everyone inside. Can we do this? The biggest such system ever built was Biosphere 2, created in the 1990s, which sustained a total of eight people for two hungry years. Can we realistically scale from eight people to one million in the next 30 years?

Nobody is spending the kind of money necessary to get answers in a hurry, perhaps because there’s no obvious profit in things like orbital obstetrics or airtight greenhouses the size of two Singapores. We still don’t know a lot of first-order stuff, and getting that knowledge is going to be expensive, time-consuming, and without an obvious return on investment.

Space is so terrible that in order to be a better option than Earth, one calamity won’t do. An Earth with climate change and nuclear war and, like, zombies and werewolves is still a way better place than Mars.

Staying alive on Earth requires fire and a pointy stick. Staying alive in space will require all sorts of high-tech gadgets we can barely manufacture on Earth.

No off-world settlement anytime remotely soon will be able to survive the loss of Earth. The Earth of 2022 puts on about 80 million people per year. If saving our ecology requires us to reduce Earth’s human population, then we need to launch and house 220,000 volunteers per day just to tread water.

A related idea is that space should be zoned for heavy industry, while Earth returns to an unpolluted Edenic state. All the nasty mining and manufacturing can be done elsewhere, with by-products cleanly disposed of into the vast landfill that is the solar system. As Jeff Bezos says, “Earth will be zoned residential and light industrial.

No place in space has something like a giant hunk of pure platinum or gold. But there is cement. It’s a major contributor to global warming, so can we make it in space? Technically, most of the components of cement by mass exist on the Moon, but they won’t be easy to dig up. Construction equipment will need to be built to function in an airless environment at low gravity with equatorial temperature swings from -130°C to 120°C. Little things start to loom in this context. Just getting a lubricant that can handle these temperature shifts without degrading is nearly impossible. The same goes for the machines themselves. At extreme cold some metals can undergo a ductile-to-brittle transition; below a certain temperature, metals behave more like stone.

However strong they may be, they can’t flex and bend. It’s speculated that the Titanic sank because its steel hull experienced a ductile-to-brittle transition before hitting the infamous iceberg. That’s a nontrivial problem when you desire to use construction equipment that regularly slams into hard surfaces.

And scaled to the needs of Earth, which currently requires over 3.5 billion metric tons of cement per year? What are the rules for dropping 3.5 billion tons of rock on Earth annually?

Part of what’s supposed to make these ideas work is cheap, plentiful energy thanks to space-based solar power.  It’s certainly true that there’s a whole Sun’s worth of sunlight in space, unobstructed by annoying Earth features like weather and the atmosphere. Exactly how much more energy you might get per panel depends on exactly what assumptions you’re prepared to make, but different estimates expect about an order of magnitude improvement. That sounds like a lot until you ask yourself what the cost differential will be between a panel in space and a panel in Australia.

Think about maintenance. Try to imagine acres upon acres of glass panels in space, regularly pelted by intense radiation and bits of space debris while enduring the extreme heat of perpetual sunlight. They’ll have to be repaired and cared for either by astronauts or an army of advanced robots. Solar panels in Australia can be cleaned by a teenager with a squeegee.

When dumping solar power back to Earth, you have another problem. Space-based power has to be beamed to huge receivers on Earth, losing energy en route. But it can’t be beamed at too high an intensity, lest it endanger birds and planes.

Space solar is valuable if you’re already in space, as a way to generate energy without burning fuel. So cover every rooftop with solar panels, followed by the Sahara desert, and then if the planet still needs energy, we can talk about space.

As for peace through allowing people to just move between settlements, well, we should consider that most people aren’t even allowed to do this between nations on Earth. Space will likely be worse. However you feel about immigrants coming to your country, one thing you probably don’t fear is the possibility that they’ll breathe too much air. In space, the atmosphere is constructed, as is the ground beneath your feet, and individual settlements will only be rated for certain population sizes. That’s not obviously an environment where you’d expect to see open borders.

For some, it’s not about homogenization, but wussification. Many American space advocates favor a version of what scholars call the Turner Thesis or the Frontier Thesis.[*] The claim is that the United States became dynamic, democratic, ruggedly individualistic, and generally awesome due to a long-standing frontier culture. Sometimes this is a simple rhetorical flourish about space as a place of newness and adventure, but often the frontier is seen as something more—as a sort of process of social resurrection. In this vision, space settlers will forge a hard, serious, creative civilization, and that borderland society will show Earth people a tougher and more democratic mode of life, just as the American West purportedly did for the United States. The problem here is that this once-popular theory is now rejected by pretty much all mainstream historians as a misleading oversimplification.

Even if it were true, if you read the original literature, the Turner Thesis relies on the idea that US settlers had cheap land, isolation from non-frontier areas, and ominously, the need to organize to seize land from the native population. Space is expensive, will have internet, and thankfully lacks a local population to exploit and murder.

A more generalized version of this frontier argument says that the harsh world of space and the need for robotics will result in a vast increase in creativity. Again, this is hard to measure and debated by scholars, but there are reasons to be skeptical that space is the optimal solution. To illustrate why, consider an idea we call the “Necrosphere,” in contrast with the Biosphere. The Necrosphere is a built structure on Earth. Inside it, the ground is poison, there is no air, and cascades of radiation are fired at the inhabitants on a perpetual basis.  Why did we build it? In the sure knowledge that we can stick engineers inside who, due to the harsh environment combined with their need not to die, will spew forth valuable ideas like a spigot spews forth pressurized water. If this sort of thing seems implausible to you, you should ask yourself why anyone would expect a Mars base to generate all these supposed benefits. You should also ask yourself why it is that so many innovations on Earth come not from anarchic wastelands but from cities where an engineer’s main hardship is eight-dollar espressos.

There are different flavors of this argument, but the most famous is philosopher Frank White’s notion of the overview effect. White, and many other people in the space community, believe that the view of Earth from space confers special insights about nature and human oneness. As he says, “People who live in space will take for granted philosophical insights that have taken those on Earth thousands of years to formulate.

If so, they don’t seem to have been forthcoming with anything terribly Earth-shaking. After almost 70 years of space flight and over 600 spacefarers, your local library contains no A Critique of Pure Reason . . . in Space, no A Treatise on Human Space-Nature. As far as we can tell, most of the philosophizing by spacefarers could fit nicely on a Hallmark card: the standard observations are that the Earth is beautiful and fragile, and that you “don’t see borders up there.”

But other transcendent experiences are available, too, generally at a lower fee. One attempt to measure the overview effect found that if it exists, the effect is about in line with that experienced by new moms. We don’t plan to make fun of new moms and alienate our audience this early in the book, but can we just agree that if every new mom got the insights of philosophers and sages,

Most damning to the theory is the fact that, while there have only been about 600 people in space, there are about 6,000 stories of astronauts behaving badly. Alcoholism, adultery, flying planes while on drugs, lying to medical staff, denying climate change, promoting pseudoscience, fighting publicly with other astronauts, and the time an astronaut drove across the country in order to kidnap her ex-boyfriend’s new girlfriend. The ex was also an astronaut and had arguably been stringing her along.

There are a few versions of this one, but we’ve found these three pretty common: space settlement will create more territory so we’ll fight less about territory; space settlement will make us rich so we won’t want to fight anymore; and space settlement will allow unhappy citizens to just leave for other settlements, which will reduce tension here on Earth. The territory argument is the most silly. Nations don’t fight over land, they fight over particular land. You can’t solve disputes over Jerusalem or Kashmir or Crimea by promising the parties involved equally large stretches of Antarctica.

The appeal to famous explorers is moving but not very convincing. Most of us are not in fact famous explorers. Most of us prefer to vacation in places that have pastries and air-conditioning, not Mount Everest or the Amazon basin. It’s cool that some people are into this stuff, but it’s hard to argue that they represent universal human nature. Some people are competitive mayonnaise eaters, but you never hear anyone say they embody deep human truth. Plus, if you actually look at the stories of explorers, priority claims seem to be at least as important as exploration. When the Peary expedition said they’d reached the North Pole in 1909, they entered into a public priority fight with Dr. Frederick Cook, who said he’d gotten there first.

One person who didn’t lay a priority claim was Roald Amundsen. He’d been planning to be first to the North Pole when he heard about Peary’s success. What’d he do? He immediately switched his expedition to the yet unreached South Pole

The second argument—the appeal to humans spreading around the world—is also questionable. Homo sapiens indeed has spread to every continent. But then so have roaches.

Modern mass migration often has to do with warfare, persecution, and starvation. It’s plausible that it was the same way in the distant past.

Humans have been in space for over 60 years now and we do know plenty about what astronauts experience. But astronauts aren’t normal people. To be frank, they’re better than us. Although this is changing a little as the era of space tourism permits the schlubby among us to reach orbit, the average astronaut is someone who combines deep specialist skills with the ability to pass a battery of physical and mental tests that most of us would bail on in a few days.  Dr. Sally Ride wrapped up a PhD in physics from Stanford before becoming an astronaut. Dr. Rhea Seddon was awaiting her turn on the Space Shuttle, she combined astronaut training with continuing her work as a surgeon, and in her spare time raised several children.

Combine this with the facts that literally nobody has been to space for longer than 437 days in a row, and the total time the Apollo missions spent in the Moon’s one-sixth Earth gravity is just under two weeks, and it becomes very clear how little we know about the most pertinent question for space settlement: can regular people flourish for long periods off-world?

A human is, to a first approximation, a pillar of liquid about two meters high, in which are suspended various moist and jiggly biological systems—digestion, waste storage, sense of balance, the movement of blood. All of these systems evolved in an environment where a 6-billion-trillion-ton sphere called Earth sat at the pillar’s foot.

The many ways to die in space

The good news from space is that it doesn’t kill you immediately. As long as the equipment is working. On Earth, air pushes on your skin from every direction with a consistent pressure of about 14 pounds per square inch, or using ridiculous non-American units, 1 atmosphere. That’s about the weight of 1 liter of water on every square centimeter of your skin. You don’t notice this for the same reason a sea bottom shrimp doesn’t notice that the surrounding liquid could implode a submarine—your body is adapted to the pressure near Earth’s surface. It counterbalances the typical push of your surroundings,

But consider a soda. When you buy a sealed bottle of Diet Pepsi, you know it’s full of gas, but you don’t see a lot of bubbles. That’s because the bottle is held at about four times the surface air pressure of Earth, keeping carbon dioxide suspended sedately inside. When you open the top, you expose its contents to Earth’s relatively gentle atmosphere. All that dissolved gas rushes out in the familiar bubbling foam. If you want to avoid the sudden burst of gas, you can always open your bottle forty meters under the sea, where the pressure will keep the gas in place,

Your body is like the soda, except that the gas suspended in your fluids is nitrogen,[*] absorbed from the atmosphere. If you were teleported to outer space, where the air pressure level is “none,”[*] your bodily fluids would react like the Diet Pepsi when opened, only instead of a burst of foam, you’d get nitrogen bubbles blocking your veins and arteries, preventing the normal flow of blood, oxygen, and nutrients. This danger is familiar to divers going from low depths back to the surface. If you switch from high to low pressure too quickly, you get “decompression sickness,” colloquially known as “the bends” because it often affects joints, causing the sufferer to bend in agony. If it’s in your lungs, that’s “the chokes.” If it’s in your brain, you’ve got “the staggers.

If you’re exposed to space, most likely you’ll just have the death. In fact, the only people who’ve ever died in space[*] were killed by sudden loss of pressure. Decompression sickness isn’t just a danger during accidents; it’s an issue any time you use a pressure suit.  Although the International Space Station is kept at Earth pressure, both American and Russian space suits only have around one third of that. So, why don’t astronauts get bendy, choky, staggery, and deathy when they don space suits? Because they pre-breathe pure oxygen before spacewalks, removing most of the nitrogen from their blood. No nitrogen, no nitrogen bubbles.

Movies may have led you to believe heroic astronauts can slip on a space suit and leap to the rescue, but under current designs this would result in Brad Pitt clutching his joints and shambling to a very painful (if handsome) death.

But pure oxygen is dangerous. In 1967, during prep for the Apollo 1 flight, a spark went off in the crew’s capsule, causing an intense fire in the pure oxygen environment. The three astronauts—Edward White II, Roger Chaffee, and Gus Grissom—could not be rescued, because the sudden increase in temperature and pressure made it impossible to use the inward-opening hatch, while the intense heat prevented rescuers from saving them.

The lack of air in space is well known, which makes it easy to forget just how many aspects of life will have to change if humans expand into space. Vacuum is potentially fatal and perpetually annoying. The risk also changes for the worse as the human presence in space increases because going to space necessarily involves objects at high-speed relative to each other. Orbital velocity is about 8 kilometers per second. Around 3 kilometers per second, if an object smacks into your spaceship it delivers roughly the kinetic energy of its own weight in TNT.

This is a bigger problem for open space-settlement concepts than for surface settlements, but regardless of where your habitat is positioned, the fact that death is ever present is going to have social and political consequences.

In a space settlement, oxygen will be created by chemical or biological means, but either way it’s going to be constructed using systems built top to bottom by human hands. Someone’s going to own those.

Assuming you have found a way to deal with the near emptiness of space, you now should think about an unfriendly presence in the void: radiation. Under special circumstances, radiation can kill fast, but the bigger concern in space is a slow but serious increase in the risk of medical issues, particularly cancer. This is especially worrisome when we imagine going from a world of middle-aged professionals doing a year in orbit to a world where children grow up in space. The need to stop radiation is one of the major factors that will shape human habitation designs off-world, and it will therefore have major effects on quality of life. The problem is that with current knowledge, it’s hard to predict the effect of radiation on the body.

As with pressure, the human body evolved in an environment with certain types of radiation at ranges found on Earth. The reason cancer and superpowers remain rare is that most radiation we experience is quietly dealt with by our bodies. The thin shell of dead skin around you provides a natural shield, and your internal machinery is reasonably good at repairing or destroying radiation-damaged cells.

The problem in space is that unless you have sufficient shielding, you get higher doses of radiation, and radiation of different types than you’d get on Earth. This radiation comes largely from two places—the Sun and the rest of the universe.  As a radiant ball of plasma, the Sun already spends most of its time blasting out hot ions in every direction. Earth’s magnetosphere and atmosphere protect you from most of these. If you’re in space, all things being equal, you’d rather avoid solar radiation, but it doesn’t cause instant death.

However, now and then, the Sun undergoes a “solar flare,” when it suddenly increases in brightness. And then there’s something worse: sometimes a solar flare is accompanied by a “solar particle event,” which is a particle event in the same sense that a tsunami is a water event. Visualize a relatively small region of the Sun suddenly ejecting a huge stream of protons that move in one direction like a flashlight beam of death. The good news about these things is that, as science fiction deity Douglas Adams put it, “Space is big.” Randomly aimed death beams will likely miss a teeny tiny human ship. But if you happen to be caught in the headlights, the result will be acute radiation sickness, whose symptoms include vomiting, skin burns, heart issues, lung damage, compromised immune system, and—if the dose is large enough—a painful death.

You may wonder what the plan is if you happen to be aboard a spaceship for this sort of thing. For near-term efforts to go back to the Moon, the procedure in the words of NASA scientist Dr. Kerry Lee is to “make use of whatever mass is available.” That is, redistribute whatever stuff in the spacecraft or station that you can find because it is now your radiation shield. Why not a dedicated radiation blocker? Because that’s a huge amount of mass that costs a lot to send to the Moon and then just sits there.

The Whole Universe Wants You Dead Sometimes a star explodes. This is rare, but happens frequently enough that space is a cross fire of the results. Although they are at relatively low density, very fast charged particles are everywhere. Most of this stuff is low mass—individual protons or helium atoms, but a small percent of the products of these explosions are heavy, fast, charged particles. These guys are dangerous. In one experiment, iron nuclei with high energy were fired into a gel-like substance to simulate what space might do to the human body. Individual iron nuclei—single atoms—blasted out tunnels as thick as a human hair.

Exposure to this “galactic cosmic radiation” is a constant part of life in space. Astronauts sometimes report “flashes of light” that only they can see, and this may be the result of their eyes being struck by these far-traveling bits of doomed stars. Current estimates say that once you leave Earth’s protective atmosphere and magnetosphere, every single cell nucleus in your body will be struck by a proton every few days, and by a larger charged particle every few months.

Radiation Is Coming for Your Equipment Radiation. It can also mess with our technology. In 1859, our planet was hit by a solar particle event that became known as the Carrington Event. That night, from California to Britain to Greece to Australia, something like the Northern Lights was observed. Streams of fire will likely be even less pleasant if you live in a built habitat where electrically powered machines are responsible for ventilation. Nothing like this has happened since, though in 2012, an event of similar power to the one in 1859 missed Earth by what astronomer Dr. Phil Plait told us was “a not-large-enough-to-make-me-happy amount.

Radiation appears to cause problems from time to time on the ISS as well. Here’s a story from How to Astronaut, Terry Virts’s memoir of life on the ISS: It was during a 2014 expedition when he suddenly heard a blaring klaxon. The crew raced to see what was up, and found the “ATM” alarm lit.  Ammonia leak!” Ammonia is not something you want in your space station. Lovely for your cooling system, but toxic for humans and hard to remove. If enough leaked in, it could render the whole station uninhabitable, and in the very worst case, extra gas might over-pressurize and rupture a module. The protocol they were supposed to follow went something like this: Oxygen masks on Float over to the Russian segment, close the first hatch Get naked Close the second hatch to seal off the American segment You might be wondering about one of those steps, but there’s a simple explanation: you seal the American segment because the Russian coolant system uses glycol, not ammonia, so if there’s an ammonia leak, it’s on the American end. Oh, step 3. Well, ammonia contaminates clothes, so for safety you should leave them back in the ammonia zone and hope the Russians have spare undies.

Radiation has caused problems farther out as well. In 2003, while the Mars Odyssey Orbiter circled the Red Planet, the Sun fired off a huge blast of radiation, which knocked the orbiter out of contact and into safe mode. One of its sensors, designed to detect radiation, was permanently destroyed. In the words of one scientist, it “choked” on the data. Try to imagine being in a Mars-orbiting spacecraft, suddenly losing contact with home, and then being informed that your radiation detector stopped working due to too much radiation.  Even if you provide thick shielding against radiation, you can still get hit by fast, heavy ions smack into your shielding that can generate cascades of secondary and biologically dangerous particles, sometimes known as a “nuclear shower.

Spallation is particularly illustrative of how mind-bendingly complex designing for space is once you get into the details. For example, if your radiation shield is super thick and is made from aluminum, you can end up being exposed to even more radiation than you would have if you had no shielding at all.

Space radiation bad. Right? Well . . . yes. Probably. We think. It turns out it’s hard to do science on this stuff. The best available data comes from lab animals, from people who’ve worked with radioactive materials, and from times when something horrific happened, such as the disaster at Chernobyl or when the United States dropped atomic weapons on Hiroshima and Nagasaki. Even these data are imperfect for assessing space radiation. For instance, atomic weapon victims got a sudden massive dose of what was probably mostly neutrons, whereas the typical experience of space involves long-term exposure to charged particles. Lab animal studies are also imperfect because their application to humans is not one to one, and anyhow it’s hard to generate space-like radiation in a lab setting. But wait, you say, we have 50 years of humans on space stations. Doesn’t that tell us anything? Sure, it tells us something, but because all space stations orbit under the protection of Earth’s magnetosphere, astronauts are exposed to space radiation at doses that are something like 2 to 3 times less than in deep space.

The only direct source we have, then, on the physiological effects of beyond-the-magnetosphere radiation comes from those Apollo missions that went to the Moon and back, the longest of which was the Apollo 17 mission, which only lasted about 12.5 days. A typical Mars transit time is around six months. The good news is that although the Apollo guys got a huge dose of extra radiation, they don’t appear to have had higher rates of cancer. That’s encouraging, but the problem is that it’s a tiny sample set—exactly 24 men. Also they’re not the least bit random—they’re ultra elites, most of them test pilots, and all of them got through medical exams that were so thorough they bordered on the sadistic, including intimate encounters with something they referred to as the “steel eel.” If these men had less cancer than you’d expect, perhaps it’s because they were just a little more robust than most of us.

Here’s a line from the 2018 paper “Limitations in Predicting the Space Radiation Health Risk for Exploration Astronauts”: “there is no definitive evidence that space radiation causes human cancer, but it is reasonable to assume that it can. Some evidence from atomic bomb survivors indicates that ovarian and breast tissue are especially susceptible to radiation damage. Because of this, a few space advocates even call for a no-girls-allowed rule for long-term Mars missions. This might put a damper on plans for population growth in a future settlement.

A recent paper by the National Academy of Sciences has argued, in short, that if we want to use veteran astronauts for a Mars trip, we must use Earth’s most powerful defense mechanism: a signed waiver.

Although astronauts are well within the pull of Earth’s gravity, their circular orbit means they are perpetually “falling” toward Earth, sort of like a roller-coaster drop that never ends. Thus, they float, just as they would if untouched by any powerful gravity. Like a roller coaster, the sensation of falling often induces vomiting, but this typically goes away in a few days. Once settled in, astronauts often describe microgravity as one of the singular joys of orbit. But it’s not great for the human body. Microgravity causes predictable physiological problems, some of which are short term, some of which may be permanent, some of which may be still undiscovered because humans haven’t spent enough time in space yet.

But you’re planning to settle space we confess to a major problem with the data. No serious space-settlement plan calls for extended life in microgravity, but this is exactly the gravity regime from which almost all space medicine data comes. The vast majority of proposals for space settlement are about the Moon, which has about one-sixth Earth gravity, or Mars, which has about two-fifths Earth gravity. Most other proposals are for rotating space stations that can artificially create regular old Earth gravity. We have almost no medical data about life in partial-Earth gravity. The best we have is the 12 guys who collectively spent less than a month on the lunar surface. If there are serious negative effects of life in partial gravity, they likely take longer to show up.

From the perspective of bones, walking around is just getting picked up and slammed down over and over again. Your body is prepared for this, but your body is a cheapskate. Bones and muscles are a use-it-or-lose-it affair, and when you’re floating in microgravity, you often don’t use it. Four months in space means about 1% loss of mass in the spine per month. While your spine is degrading, it’s also lengthening in zero gravity. Because of this, lower-back pain is quite common in space and postflight. According to an account by Mike Mullane, on a 1984 flight, the five men aboard had serious back issues. The only person without pain was the lone female flyer, Dr. Judy Resnik. Mullane recalls her saying, “I don’t believe it! Here I am going to bed with five men, and they all have backaches.

Muscles suffer a similar fate to bones. One study of ISS astronauts found their calf muscles had shrunk 13% after six months in orbit. That might not sound too bad, but note that during those six months the astronauts were doing regular multi-hour exercise routines. Most spacefarers are back to normal after a month or two on Earth, but in some cases it can take six months to three years. So after a little time in space, you’ll have osteoporosis, weak muscles, and back problems. And, by the way, all that lost bone calcium can contribute to constipation and renal stones. You have left the cradle of Earth for the nursing home of orbit.

Astronauts are still expected to put in 2.5 hours of exercise a day, 6 days a week, to slow muscle and bone deterioration. This is despite the fact that space exercise is the most frequent source of space injury.

For a space settlement with partial-Earth gravity, it’s possible that settlers could simulate Earth gravity by wearing weighted clothing.  As to what the effects would be on a developing human child, we haven’t got a clue.

We sometimes think of our circulatory system as a pump with pipes. The heart beats away and blood goes where it needs to go. This is kind of true, but substantially too simple. Blood above your heart just has to fall down to reach it. Blood in your feet needs a good strong push to make its way upward. Well, unless you’re doing a handstand, in which case it’s reversed. In a way that is unimaginable for the plumbing of a house, your circulatory system stays functional whether you’re flat on your back, lying sideways, or hanging upside down. But when you stay in zero gravity for a while, things get weird. Your legs pump away as if they’re still fighting the gravity humans evolved with. Fluid shifts upward, causing your legs’ fluid volume to decrease. The result is what one paper referred to as “Puffy-Face Bird-Leg” syndrome. Plus, with your body baffled by various fluids being up so high, you’ll make more frequent trips to the bathroom. During the trip, their bodies will forget how to manage blood flow against gravity, possibly causing dizziness or even fainting as they exit the landing craft.

Our best countermeasure to date is pretty low tech: drink something salty like consommé or sports beverages. Load up on electrolytes and fluid before you return to normal gravity, raising your blood pressure and getting your total fluid load close to normal.

Microgravity appears to screw up your vision. We don’t know why, but the best guess is that the upward fluid shift increases the pressure in your head, altering the shape of your eyeballs and the blood vessels that feed them. Problems appear to get worse the longer you spend in space. In one survey of three hundred astronauts, 23 percent of those who went on shuttle missions reported difficulty seeing things close up after coming home. That’s pretty bad, given that shuttle missions tended to last around two weeks or less. Among those who did longer duration ISS trips, the numbers rose to 50%. The problem is more common in astronauts over 40, so they are prescribed spectacles in anticipation of farsightedness.

There is a possibility that space conditions have cognitive effects. Frankly, between the radiation and the fluid shifts, cumulative brain damage doesn’t sound like an especially wild conjecture. If this is a subtle issue that gets worse over time, it’ll take on a lot of importance for any space-settlement plan.

Suppose you spend ten years adapting to Mars gravity. Can you come back to Earth? We don’t know, and we really don’t know the answer if your ten years started at age zero.

There aren’t any great countermeasures here, but one device tested over the years puts your entire lower half in reduced pressure to convince your fluids to head south. These “pants that suck,” as Scott Kelly referred to them, may come with risks. According to his account, a cosmonaut using them once passed out as his heart rate dropped.

Life in partial gravity may not produce the same sort of damage, but if it does, space settlements will have to plan for relatively serious vision impairment in most of their citizenry.

The basic job of a trauma surgeon is to make sure you’re breathing and not bleeding too much—things that should be done on-site as quickly as possible, ideally in a matter of minutes. But even in the ISS, which is only a few hundred miles from Earth’s surface, evacuation takes 6 to 24 hours.

After a long space journey, spacefarers have all the bodily weakness issues we described above, plus short-term effects pertaining to the change in gravity regime, such as nausea, dizziness, and clumsiness.

Unless there’s a dedicated sick bay with a proper air-filter system, space-settlement surgeons won’t have an ideal operating room. This is especially true in microgravity, where food, microbes, and bits of human waste may be floating around. If surgery is required, the doctor must be trained for the particular gravity regime they’re working in. For instance, according to one paper, blood “tends to pool and form domes that can fragment on disruption by instruments. Although there has never been a dedicated medical center in space, space settlements will need them.

Well, you’ll at least get some anesthesia? Yes, but you can’t use inhaled anesthetics, because if there’s a leak, you’ve just released laughing gas into the sealed atmosphere. Another option is spinal anesthesia, but with your fluids shifting upward, the anesthesic might not end up where you want it to go. Your best bet will likely be injection at the site. And by the way, it may not work right. Evidence suggests that human bodies don’t absorb nutrients and medication at the same rate in zero gravity. This isn’t surprising considering all the fluid shifting and the fact that your stomach contents float, but it does mean that any medication, especially serious stuff like anesthesia, will need to be recertified for each new gravity regime. Incidentally, you may be wondering how we know so much about zero gravity trauma surgery. How many dramatic trauma surgeries have been performed in space? The answer is zero. The curious reader will be referred to the copious scientific literature containing the words “porcine” and “parabolic,” with titles like “Cardiopulmonary Resuscitation in Microgravity: Efficacy in the Swine During Parabolic Flight.” Parabolic flights are a common way to test equipment and protocol in simulated weightlessness. In short, if you fly a plane in a parabola with just the right arc, you get about thirty seconds of free fall. Do this over and over frequently enough and you can get a good hour of simulated weightlessness in a single day. And if you bring along a dead pig and some very very very very very dedicated medical practitioners, you can find out a thing or two about space medical procedures.

If someone spurts blood on the Moon, it’ll fall in slow motion, but it will eventually find its way to the ground and ideally a drain. The bad news is that you’ve got an unfamiliar environment with tight working conditions, limited supplies, and no ability to helicopter your patient out to the trauma ward. Accidents should be planned for. Any near-term space settlement will be an active construction site employing workers who grew up in a totally different environment. Trauma medicine is a must.

We have no data on long-term effects of radiation on human bodies outside Earth’s magnetosphere. We have almost no data for partial-gravity regimes. We have almost no data on people with chronic health issues.

Kids in space

Sex probably “works” in zero gravity. In the mechanical sense. Mind you the physics will be a little tricky because every action has an equal and opposite reaction. Those who attempt the act “may thrash around helplessly like beached flounders until they meet up with a wall they can smash into. We’ve seen more than one proposal for what one author called an “unchastity belt”—a sort of elastic band for two. Another concept is the “snuggle tunnel” for anyone who’s ever wanted to experience lovemaking in a narrow, poorly ventilated pipe. There’s also the 2suit, which would keep a couple connected

Imagine this: you’re informed there’s a drug that’s really fun, but that results in slow bone loss, major fluid shifts inside the body, renal stones, muscle weakness, dizziness, and eyeball damage. You might still take it if all the cool kids are doing it, sure, but you’d be substantially more careful if you were carrying a baby in your body. Replace the drug with space and you understand why you shouldn’t quit birth control in orbit. Space has potential negative effects at every stage. Sperm and eggs are subject to constant radiation well before anyone dons a 2suit. So is the resulting fetus, and the developing child, and the developing child’s gametes. Remember that mom’s bones will be weakened in microgravity and perhaps also under only partial Earth gravity. A serious open question is whether birthing is safe with a weakened pelvis. For the baby, the time after birth is especially worrisome. The main current method of preserving bone health in astronauts is exercise, but you try getting a three-month-old to conduct resistance training for three hours a day. Another issue at every stage from conception to adolescence is hormones. For instance, there’s some evidence of hormonal changes in astronauts, such as lowered testosterone in males.

Mars in particular may produce hormone problems. Martian soil is quite high in perchlorates, a class of chemical that messes with thyroid hormones.

Also, what kind of atmosphere are we raising our kids in here? If your settlement is like the ISS, it’s one with abnormally high CO2 levels. That alone would be a novel environment for baby construction, but there may be other issues; when any new equipment goes to the ISS, it has to be carefully checked for what volatile organic compounds it emits. Think about it this way—when a new computer arrives at your house, fresh from the factory, you don’t really care if a bunch of weird synthetic gases waft out. You just think to yourself, “Good thing I don’t live in a tiny sealed atmosphere!” and go on with your day.

A complaint made by both Scott Kelly and Terry Virts regarding their time on the ISS, which would also be familiar to people who work in submarines, is the high level of carbon dioxide in the atmosphere, which can lead to headaches.

If humans do have major reproductive issues off-world, it’ll be extremely hard to know why. Suppose tomorrow you had a Martian settlement and observed a rate of developmental abnormality that was three times normal. Where do you point the finger? Maybe it’s the altered gravity or maybe it’s the radiation. Maybe it’s the radiation but only in concert with an altered microbiome and the stress of trying to survive in a hostile environment. Maybe it’s some ultra-low-concentration SMAC gas nobody’s paying enough attention to. And if you’re talking about a child conceived and born in space, you also have to think about time—did the problem arise in the parents’ gametes, in utero, sometime after birth, or what?

While we don’t have systematic or long-term data, what we can say is that the available experiments indicate that there’s not a chance in hell we would want to try having and raising kids in space. Experiments show that radiation causes havoc for gametes and that microgravity may damage cell cytoskeletons. In case you don’t remember high school biology, these are the structures in a cell that give the cell its shape, kind of like the wooden beams in the walls that hold up your house.

We are not saying that any of this is impossible to solve. But as with space medicine generally, getting the knowledge we’d need to have reproduction in space that is safe and ethical would be a massive, costly, decades-consuming affair, and strangely, among people advocating for vast space settlements in the next thirty years, nobody is doing the sort of enormous spending necessary to get answers.

A commonly proposed solution to a lot of these issues is to perform some sort of genetic engineering. There is at least one book entirely devoted to the question of genetic modifications in space, and it includes proposals that range from prolonging human life spans to altering the ABCC11 gene, responsible for armpit stink in some populations, as a way to improve social harmony. Single-gene edits are possible, but we suspect more complex ideas, like radiation-resistant outer skin or genetic alterations to help bones in microgravity, are a long way off scientifically. It seems pretty straightforward to us that creating new humans adapted specifically to hostile space environments far from the home world purely so they can settle it is morally dicey. If there were some kind of extreme urgency for human migration to Mars, perhaps this sort of thing could be argued for. But there isn’t.

Psychological problems

You might wonder why astronauts—elite superhumans doing their dream jobs—have psychological issues at all. The short version is that space on a day-to-day basis isn’t so great. It’s not the least bit Star Trekky. There are tedious chores: meal prep, cleaning the bathroom, scrubbing mold, taking inventory. Private accommodations are the size of a coffin, funny smells waft from the waste containment facility, the food is mediocre, exercise clothing gets reused for more days than Earthlings would dare. Bits of human waste frequently find their way to airborne status, as do sloughed-off foot callouses from feet that no longer strike the ground. The equipment is quite loud, it’s hard to get enough sleep, and historically space stations are pretty crowded. The ISS has about the habitable volume of two average American apartments, but it contains six people, all their equipment, food, exercise stuff, experiments, and every kind of astronaut waste from food containers to feces. Schedules are packed with experiments, public relations, and maintenance work. All of this is punctuated by occasional emergencies, which have historically included fires, near-drowning in a space suit, and the need to rapidly locate a leak in the space station.

The optimal astronaut is a sort of hypercompetent Ned Flanders—reliable, even-tempered, a bit boring, and also the kind of person who could perform brain surgery in a flaming jet if called upon to do so.

The Moon is close enough to Earth that you can have something like a live conversation with a psychiatrist. Mars is not. At greatest distance, it takes 40 minutes for a signal to get from Earth to Mars and back. Communication will be more like letter writing than full conversation.

Astronauts also regularly receive little gifts with resupply. In one recent case, a scientific refrigerator was sent up preloaded with ice cream—no doubt a welcome break from typical space fare, which often consists of lukewarm food packets. Resupplies also bring fresh fruits and vegetables, which provide benefits beyond taste and nutrition. For Viktor Patsayev’s in-space birthday on Salyut-1, he celebrated with a fresh lemon and onion. Anatoliy Berezovoy and Valentin Lebedev craved fresh onions so much they once ate the miniature ones meant for an experimental cultivator on Salyut-7. For Foale, the scent that brought him home was fresh apples. Resupply also brings little surprises for holidays and birthdays. Especially beloved are care packages from friends and family. These are often very simple things—Dr. Shannon Lucid recalled Mir cosmonauts appreciating perfumed letters from the women in their lives. Lucid herself was pleased to receive Jell-O and a big bag of M&Ms.

One fact of human psychology we found even in old polar exploration diaries was a deep concern with celebrations and with food. Crews on those monotonous trips often celebrated whatever holidays they could lay their hands on as an excuse to bring some novelty into the world. Today’s ISS crews receive themed care packages for things like birthdays and holidays. Mars can only be reached once every two years, but it might be smart to mimic the ISS and send up impossible-to-get Earth goodies for distribution on special occasions.

Cosmonaut Anatoliy Berezovoy loved cassette recordings of nature during his 211-day flight in 1982, recalling, “We had recordings of sounds: thunder, rain, the singing of birds.

The question for a would-be space settler isn’t “Where’s the good place?” It’s “Where’s the survivable place?” Options are limited. Space is big, yes, but space-settlement sites are few. Until we reach some extravagantly more advanced level of technology, there are only two worlds we can hope to settle—the Moon and Mars. Mars has about the same land surface as Earth, but that’s only due to the lack of any oceans. The Moon, similarly unencumbered, has about as much land area as 1.25 Africa’s. The only other serious possibility would be the construction of a massive space station—a very hard project.

The moon

If you build a Moon settlement, the defining feature of life will be things lacked. The Moon has almost no carbon on its surface. What little carbon can be found has been deposited by solar wind and space-object impacts in minute quantities over billions of years. This is a problem, because humans just can’t get enough of the stuff. We are about 20% carbon by mass. Plants are worse. Trees, for example, have a dry weight consisting of about 50% carbon. Plus, the Moon’s surface is low in other important stuff, like nitrogen and phosphorous. Life as we know it literally cannot construct itself with what the Moon offers.

At the moment, there are precisely six small caches of high-concentration carbon on the Moon—the Apollo Moon landing sites, where the Heroes of the Space Age left behind a grand total of 96 bags of feces, urine, and vomit. Sadly, you are legally forbidden to use these precious historical artifacts.

The Moon is also dry. There is some water bound up in the lunar surface, but then, there is water bound up in concrete. In fact, going by the latest estimates, concrete is comparatively moist. We did a back-of-the-envelope calculation and estimated you’d need to cook all the water out of six tons of lunar soil to get the three kilograms of water you need daily to survive, not including cleaning, showering, and the occasional water balloon fight.

The Moon also lacks a radiation-thwarting planetwide magnetosphere. Nor does it have a thick blanket of atmosphere, which is handy when you want to breathe. It’s also handy because it provides protection against radiation and meteors.

The lack of protection also affects the ground itself. Earth’s surface has wind and water and the general sloshy squishiness of a living world. The Moon’s surface is the result of billions of unhealed wounds—violent impacts from space objects large and small. The heat of these strikes fuses the surface while shattering what came before, and this fuse-and-shatter routine happens over and over for eons. Add to this the regular fracturing that comes with extreme heat followed by extreme cold, and the result is that the Moon is coated in “regolith,” from the Greek roots meaning “blanket of rock.” Nasty little jagged bits of stone and glass.

On the plus side, you’ll come to really appreciate lunar sunrise, mostly because it arrives just once every two weeks. Lunar nights are Earth fortnights—two weeks light, two weeks dark. Combine this with the lack of oceans and atmosphere to moderate climate and you get regular equatorial temperature swings from -130°C to 120°C, with temperatures as low as -250°C recorded in a crater on the South Pole. That’s bad for equipment, bad for humans, and two weeks of darkness is decidedly undesirable if you’re trying to generate solar power, which you probably will be.

If we’re talking about local minerals that you might refine and ship back to Earth for a profit, the Moon harbors nothing worth getting. The economics of spacefaring are changing, but in order to be exportable, for the foreseeable future any goods mined in space for sale on Earth need to be high value, low mass, and fairly easy to acquire. Nothing on the Moon matches this description. You may have heard otherwise. A surprisingly large number of books that discuss Moon settlements mention something called “helium-3,” a valuable helium isotope. We have been forbidden by our editors to go on a ten-page rant about helium isotope economics in a pop-science book, but if you want to see a nerd hyperventilate, buy us a beer and ask about it. In short, helium-3 is more common on the Moon than Earth, yes, but still extremely diffuse. We’re talking parts per billion. One estimate suggests it takes 150 tons of regolith to produce a single gram of helium-3.

What’s it good for? In a single sentence: it’s good for a small set of medical applications and for a futuristic type of fusion reactor, which would work great except that we can’t build it yet, and almost nobody is trying to build it, because it’s far harder to make work than more typical kinds of fusion reactor we also can’t build, and which use a far cheaper, more plentiful fuel, and anyway helium-3 is a by-product we already make with a well-known nuclear power source called a heavy-water reactor.

So, that’s the Moon: hotter than a desert, colder than Antarctica, airless, irradiated by space, lacking in carbon, and with no minerals valuable enough to sell back home. It’s not obviously gold rush territory. Oh, and what are the long-term health effects of living in one-sixth Earth gravity while inhaling glass? Your guess is as good as ours.

The Moon is an excellent place for rocket launches. From an energy perspective, the hard part of spacefaring isn’t traveling a long distance, but getting off-planet in the first place. On a trip to Mars, most of the propellant you will ever use gets burned up reaching a stable orbit above Earth. Once orbital, a relatively modest use of propellant will sling you elsewhere. Throw in the fact that the Moon hasn’t got a pesky atmosphere to slow down launches, and you’ve got a great platform for throwing things into space, at least compared to Earth. To be clear, setting up a launch facility on the Moon would be very hard. A lot of your mass will have to be expensively sourced from Earth. Some construction materials can be generated lunar-locally. The Moon’s surface is high in silicon, aluminum, magnesium, iron, and titanium. Silicon has all sorts of applications, from windows to photovoltaic solar panels. Aluminum, iron, and titanium are all excellent building materials. Magnesium is easy to work with due to its low melting temperature, though it has the downside of reacting explosively with oxygen, a popular gas among humans.

Noting that you can make photovoltaics from metals and silicon is kind of like noting that you can build an airplane because the dirt below your lawn contains aluminum, iron, and carbon. Focusing on elements can disguise some serious complexity. Working with titanium, for instance, requires tremendously high temperatures in specialized furnaces. The silicon needed for solar panels begins life as jagged dust or compressed stone. Trying to work with lunar iron is kind of like trying to build steel beams from a pile of rust.

The moral of the story: beware of nerds ticking off lists of mineral content, unless they also happen to be carrying a futuristic limitless energy supply,

The Moon no longer produces lava flows, but it once did.  Recent evidence suggests that at least in some cases lunar caves may have temperatures that are reliably Earth-like, in the range of 17°C. These caves may provide a prebuilt hole in the ground with protection against radiation, micrometeorite impacts, and wild temperature swings. But lava tubes will be difficult to access safely due to their sheer size.

And we just don’t know that much about them. Their stability remains a hard-to-assess question. The strongest evidence for lunar lava tubes’ size (and, indeed, presence) is observations of collapsed segments. That’s not the most reassuring information imaginable.

The Peaks-of-Pretty-Much-Eternal Light. Parts of the rims of the North Pole’s Peary crater and the South Pole’s Shackleton crater are illuminated more than 80% of the time. This is tempting stuff for homesteaders: First, if you’re using solar power, you can get energy on a consistent basis instead of dealing with two-week-long stretches of night. Second, because you’re perpetually grazed by light, rather than alternately blasted and deprived, you can get a less volatile and more mellow temperature.

And it is around -70°C, which is merely about 10°C colder than the average temperature in Antarctica.

But you also want permanently cold domains of shadow, because thanks to their extremely low temperature, some of them appear to have held on to water ice.

At these temperatures, ice is more like stone than the stuff in your freezer. It also contains other compounds, like methane, hydrogen sulfide, and ammonia. These are potentially valuable chemicals, but are also toxic and will have to be separated out before anyone takes a drink. Some of these chemicals contain precious carbon, but sadly, even after harvesting the Apollo poo bags, your combined carbon total won’t be nearly enough to start the farm.

Still, if you can get a base on one of these craters, with their combination of perpetual darkness and (almost) perpetual light, you’ve got solar power and water. That means almost everything in space.

See, your friend H2O is the jack-of-all-space-trades. You can drink it. You can crack it into oxygen and hydrogen, then use the oxygen for air. And in the right forms, hydrogen and oxygen can be reacted back together for rocket propellant or fuel cells. As long as you have a lot of energy, water means survival, mobility, escape,

Using optimistic numbers, the Craters of Eternal Darkness only make up 0.1 percent of the lunar surface. They also don’t have that much water—perhaps as much as 100 million tons. That sounds like a lot, but it’s about the weight of one tenth of a cubic kilometer of water. So, the total amount of water hidden in Eternal Darkness may be roughly equivalent to 10% percent of the volume of Sardis Lake in Mississippi, which has a huge advantage over water-laden Moon craters—it gets replenished over time periods shorter than eons. If the water is mostly used as part of a human habitat, and you get very good at recycling, it can go a long way. If the water is used for rocket fuel, once the burn is over, it’s gone. And the Peaks? By one estimate, they are one one-hundred-billionth of the lunar surface. Doing a little math, that’s less than two tennis courts. You can spread out farther if you raise your solar panels up on platforms or if you’re willing to take even less perpetual light, but the point is that while the Moon itself

Almost nobody wants to settle the Moon as an end in itself. Because most of its value is positional, and because it lacks the resources to sustain life, the Moon is mainly enticing as a stepping-stone elsewhere.

Settling on Mars

Mars is nowhere near being a Plan B home for humanity anytime soon. Consider a worst-case climate scenario. The oceans have swollen ten meters higher, drowning New York City and Boston. Low-lying countries like Belgium and the Netherlands have been swallowed up whole. Heat waves make parts of the Southern Hemisphere uninhabitable as the planet is ravaged by floods, droughts, wildfires, and massive tropical cyclones. More than half of the world’s species die, coral reefs become bleached skeletons, freshwater sources from snowpack melt away or are fouled by rising seas, tropical diseases make their way into formerly temperate climates. Crops fail, people starve, and violence breaks out as over a billion climate refugees beat against the closed gates of the comparatively livable North. Yet this is Eden compared to Mars or the Moon. That Earth still has a breathable atmosphere and a magnetosphere to protect against radiation. It is the one world in the solar system where you can run around naked for ten minutes and still be alive at the end.

Like the Moon, Mars is covered with dead regolith. There is some weathering from the blowing wind, but not enough to prevent jagged particles. And Mars has something extra—the Martian surface is poisonous. Perchlorates, a class of chemicals are found in trace levels on Earth. On Mars, perchlorates make up 0.5 to 1.0 percent of Martian surface soil.  Perchlorates are a pretty nasty chemical. At high doses, they cause thyroid problems by competing with the iodine ions your body needs to produce certain hormones. This is probably not good, especially for developing fetuses and children.

Like the Moon, Mars is covered with dead regolith. There is some weathering from the blowing wind, but not enough to prevent jagged particles.

On Mars, you get less than half the sunlight per area that Earth and the Moon get. And that takes us to the biggest problem for Mars settlement: distance. Without some exotic propulsion system, your trip inbound is going to take about half a year each way. We’re talking about six-month voyages in a tight ship, minus fresh apples Six months of food, six months of water, six months of undies and toothpaste, assuming no redundancy.

Once you’re partway into your trip, you cannot go home until Earth and Mars are about to sync up once more. This is risky. When the service module for the Apollo 13 mission experienced an explosion en route to the Moon, part of why the men survived is that physics provided a very short “free return trajectory” back home with a minimal use of propellant. If something goes wrong on Mars, you’re likely on your own.

You can’t even get a real-time phone call to help with surgery or repairs. At the greatest Mars-Earth distance, a signal takes 22 minutes each way. At shortest, three minutes.

And like on the Moon, there don’t appear to be minerals with economic value for export to Earth. The proposals we’ve read sometimes talk about deuterium, a hydrogen isotope found at higher concentration on Mars. This is even less plausible than helium-3 on the Moon because it’s farther away, worth less, and is readily available on Earth. Others talk about finding rare elements on Mars, which in fairness hasn’t had several millennia of being mined by humans. But we don’t know if such elements are easily accessible, and even if we did, getting a rare-element mining operation running on Mars won’t be happening anytime soon. For these reasons, even among enthusiasts, return on Mars investment plans tend to focus on services rather than goods—things like tourism, scientific research, and media sales.

The climate is surprisingly decent, at least by the standards of space. The typical behavior of a non-Earth planet encountering a human is to cook it, freeze it, or crush it. Mars certainly does have its freezy parts: the planetwide temperature average is -65°C, and the poles get as low as -140°C in winter. For comparison, Earth’s record low temperature is -89°C, experienced at Vostok Station in Antarctica in 1983. However, toward the equator at summertime, Mars gets around 21°C—room temperature. Add in the Earth-like 24.7-hour day, and it’s practically home, notwithstanding the endless lifeless horizons and the poison storms that shroud the world in darkness.

A rotating station in space

So, the Moon and Mars are your best options. But as we discussed in our look at space medicine, it’s at least possible that partial gravity will create major long-term physiological issues. If so, the next best option is likely to be gigantic rotating stations built in space. Any near-term design for such a station will likely be built from parts created on Earth. But Earth is a pretty deep gravity well to rocket out of, and typical proposals for open space settlements require millions of tons of material. Let’s suppose you can launch fifty tons of stuff per rocket—about as much as the largest rockets ever launched from Earth. A million-ton space station would require 20,000 such rocket launches. For this reason, proposals generally require the material to be harvested from the Moon or from asteroids, then fired to an in-space construction site.

The basic setup then is to build a technically complex launch facility off-world, then create a catcher’s mitt to receive hunks of mass that are not especially promising as industrial inputs, and then convert all that into the most complex built structure humanity has ever contemplated. That sounds hard. Can we make these things a lot smaller perhaps? Probably not. In order to walk around the rim of a spinning wheel without getting nauseated, the wheel needs to be really really big. If it’s not clear why, consider an extreme case: you’re in space, and the radius of the wheel is precisely the same as your height. Imagine the wheel is spinning so quickly that your feet push into it with the force of Earth gravity. However, your head is at the center of the wheel, experiencing far slower rotation—something close to zero gravity. Effectively, the top of you is floating and the bottom of you is planted. Thus, the middle of you decides to puke. So you need a bigger wheel, but how big? At two rotations per minute, you need a diameter of 450 meters to hit one Earth gravity. If you up the rotation to four per minute, you can pull it off with about 112 meters in diameter.

But how is a human who is spinning around at four rotations per minute going to feel? Honestly, we don’t really know. The studies that have been done often use small sample sizes, don’t last very long, and frequently are done on people who are known to be less susceptible to motion sickness. Even if we assume the best case, where you only need 112 meters diameter, that’s still far more ambitious than anything we’ve ever built. The ISS, which cost over $150 billion to construct, is about 112 meters long at its greatest length, but doesn’t include a huge habitable wheel around its rim.

And smallness creates its own problems. A small wheel has to be pretty clever to avoid what you might call the “washing machine effect.” Take a washing machine, put a heavy towel to one side and start it spinning. Inevitably, you hear a worrisome KA-CHUNK KA-CHUNK KA-CHUNK. This is what happens when a spinning object is unbalanced, and it’ll be extra embarrassing if the wheel is a tiny bubble of life in a hostile void. The solution is to counterbalance the source of the KA-CHUNK. For instance, you can have a hydraulic system that shifts water around to maintain the right mass distribution. This strikes us as terrifyingly vulnerable to Murphy’s Law. As one paper notes: “A major shift of weight (all the crew to dinner at one sitting) would require a programmed and controlled counter-movement of ballast.

Even if we could pull all this off, there remains a great big “why bother” standing in the way. In order to build a 400-meter-wide wheel in space, you have to assume we’ve already got the technological level necessary to build launch facilities on the Moon or to field great big asteroid-trawling spacecraft, not to mention outer space factories capable of converting high-speed cargos of regolith into orbital suburbs. But if we have that level of know-how, why not just use that capability to remain on the Moon or Mars, where all this stuff we’re launching is just sitting around? Is there any justification for building these things?

We’ve seen repeated claims that an advantage of space stations will be the ability to completely control things like temperature, light, and weather. This sounds compelling until you realize it’s also a thing that happens in, like, buildings. Even if it becomes possible to build all this stuff in an environmentally neutral way, you’d have to get around 80 million people into space per year just to keep the population stable.

That’s about 220,000 people per day.

There are a few good arguments for space stations under particular conditions. First, babies. Since you are now an expert on space sex and its consequences, you are aware of the concerns about life in partial gravity. In a world where the Moon’s and Mars’s partial gravity are bad for human flourishing, we might have to await the coming of space-wheel technology before we can settle space. That still wouldn’t necessarily argue for space stations as the default mode of off-world life, since they could just be something like orbital nurseries.

Moon, Mars, and space stations are the most common proposals for space settlement, but not the only ones. However, everywhere else is so very much worse. Here, we provide the alternatives, ranked and ordered by increasing awfulness.

Colonizing asteroids & Venus & Mercury

The asteroids in the belt are even farther out than Mars, meaning solar power is limited. Also, despite what Star Wars told you, many asteroids aren’t solid potato-shaped rocks, but “rubble piles.” Zero-gravity rock and dust are not great as a landing surface. Also they aren’t very close together. If you’re parked on one asteroid, you likely can’t even see another with the naked eye.

Don’t visualize a giant hunk of platinum—we’re still talking about ore with only a few grams per ton of precious metals. This is your best bet for asteroid money, and right now it’s not very good. More important for our purposes, it offers no reason to create a settlement.

Venus’s average daily surface temperature is over 450°C—hot enough to melt lead. You won’t mind because you’ll have already been crushed by an atmospheric pressure more than ninety times Earth’s. That’s assuming you survived the sulfuric acid clouds on the way in. On the plus side, the thick atmosphere will provide your remains ample protection against radiation. We haven’t found too many proposals for a Venusian habitat, but there are a few ideas for a floating base in that thick atmosphere. It turns out that there’s a slim shell of the Venusian sky that has human-friendly temperatures and pressure, low radiation, 90% Earth gravity, and access to atmospheric carbon dioxide. Location, location, location! If you’re somehow not impressed by the idea of a life spent dangling above and below hell, you should talk to the people who proposed a project called Cloud Ten that would use all that atmospheric carbon dioxide to grow bamboo and kombucha, out of which to build small cell-like habitats.

Mercury is like the Moon, but nudged much closer to the Sun, with the result that the average day-night cycle produces temperature swings from -180°C to over 425°C. In fairness, the temperatures are a bit milder at the poles, and like with the Moon, we think there may be ice there, permanently frozen in deep craters. But Mercury is not a popular settlement choice, outside of a few wacky proposals—the best of which involves settling the terminus. What’s the terminus? The little region where day meets night. The Goldilocks zone where you’re not frozen to death or cooked alive. The one downside is you have to stay safely in the penumbra as night makes its way around the planet. The good news is that the Mercurial equator is a mere 15,325 kilometers around—well under half the circumference of Earth. Better still, the Mercurial day is a leisurely 4,222.6 hours long. So all you have to do is move every bit of human civilization on the planet 86 kilometers every 24 hours forever, and you get to stay alive.[*] Or, anyway, at least not killed in particular by the cold or heat. You’ll still have the radiation, lack of air, and constant regret over your life choices.

The Outer Solar System

One thing the worlds beyond the asteroid belt have in common is darkness. Once you’re much past the asteroid belt, the Sun is almost useless as a settlement power source. The planetary landing sites aren’t so great either. There are a few tantalizing moons spinning around Jupiter and Saturn—worlds like Enceladus and Europa that likely have warm subsurface water. If your goal is to find alien life in the solar system, these are great candidates. If your goal is to be that alien life, you’re better off closer to home. Using current methods, doing the trip safely is going to take you years, possibly decades depending on where you’re going. Until we have some very futuristic propulsion technology, these places will remain the magisterium of robotic space probes.

Other Suns

The nearest star, Proxima Centauri, is about 4.2 light years away. If we assume you’re going as fast as the Parker Solar Probe, which Guinness World Records says is the fastest-ever spacecraft, that’s about 8,000 years. We can’t do this. Look, your only option for interstellar travel using anything remotely like near-term technology is to build a ship inside of which a human civilization can survive and reproduce for 400 generations without killing each other. Does that sound like something humans can pull off?

If you’ll allow a little sci-fi technology, maybe we can have ultra-long-term hibernation. Actually, come to think of it, this is probably more plausible than the 400 generations of harmony. That said, you’ll still need to build a spaceship with no major technical malfunctions during the next eight millennia. Go ahead and splurge on the nice paint.

Shameless promotions

From the late ’80s through today there have been countless shameless promotions interfacing uncomfortably with the final frontier. We can’t document them all, but here are a few highlights:

1990—Tokyo Broadcast System pays to fly journalist Toyohiro Akiyama to Mir aboard a rocket covered with advertisements for Japanese companies, including Unicharm, maker of disposable hygiene products.

1996—Pepsi sends a 1.2-meter-long inflatable fake Pepsi can to Mir, which cosmonauts have to take on more than one EVA (extravehicular activity), aka a spacewalk, aka the most dangerous activity available in low Earth orbit, and which doesn’t typically involve gigantic novelty soda cans. Incidentally, although both Coke and Pepsi have made their way to space, they aren’t terribly popular with astronauts, because burping in zero gravity is a dicey proposition.2000—Pizza Hut plasters their logo on a Russian rocket. One year later, they make the first pizza delivery to orbit. They had earlier looked into projecting their logo onto the Moon itself, but changed their minds after being told the laser projection would need to be the size of Texas and would cost hundreds of millions of dollars.

Other issues

So far we’ve dealt with a lot of stuff space does that is weird. Gravity, radiation, crazy temperature swings, and so on. The basic solution to all these problems is to avoid them if you can. What that means specifically can vary, but will always be some sort of bubble world that has to perform all the functions of Earth’s biosphere, only in miniature.

Ecosystem design is another one of those weird space-settlement problems that gets relegated to the margins while being a major practical barrier to off-world survival. Much like human reproduction in space, ecosystem design is a wickedly complex scientific problem that is only lightly funded despite being fundamental to any space-settlement project.  Perhaps because it involves uncool stuff like growing mangos and recycling poop. Or maybe because it’d be really expensive without any clear geopolitical clout for whomever builds it.

Space settlers will have to receive shipments from Earth for a long time, but at least for basic things like food and water, they’ll need to strive for as much independence as possible. Potato salad starts to get expensive when it has to be boosted out of Earth’s gravity well, flown across the void, then gently deposited outside a Martian airlock. Also, growing local produce means a higher chance of not dying if a shipment doesn’t make it or arrives contaminated.  If you’re trying to create Eden, and the truth is that human waste is substantially closer to garden perfection than the dead soil of other worlds. But so far, no solid waste has been recycled in space. Given the utility of waste off-world, a likely setup will involve some sort of composting system for human outputs. This is well-understood technology on Earth, but rarely employed in places with low gravity and a sealed atmosphere.

Food in space is subject to a lot of constraints. It has to be nutritious. It has to come in a convenient easy-to-prep container that doesn’t leach chemicals into the food. It has to be shelf stable for as long as possible. It has to produce no crumbs or other little food bits that’d find their way into the ship’s atmosphere or equipment. Complicating matters, you may not have a kitchen. Not a real one, anyway. Mir and Skylab both had refrigerators, which allowed for delicacies like filet mignon, ice cream, and Jell-O. But refrigerators take up a lot of space and energy. The ISS only got one in 2020. Most food is either room temperature or hot. But never piping hot and certainly not freshly fried or roasted—activities that might off-gas undesirable chemicals into the sealed atmosphere. Heating is only done via hot-water injection or in a convection oven that can only get to about 75°C.

In space settlements, the atmosphere will have to be recycled. The desire of humans to have cooking procedures like those from Earth will have to be balanced against the costs of scrubbing the atmosphere.

Shelf-stable tortillas have remained the astronauts’ bread of choice ever since. On the Russian side, a more technical approach has been taken. Cosmonauts eat tiny squares of bread specially engineered to be low crumb. Because of their size, they are jokingly referred to as Barbie bread.

Plants clean the air while creating more organic matter on lifeless worlds. They also provide nutrients like vitamin C, which are hard to keep shelf stable. Lack of vitamin C produces scurvy, and while that would give the operation a charmingly piratical flair, settlers would probably prefer not to have bleeding gums, wiggly teeth, and wounds that won’t heal.

You may have read a popular article or two saying that experimenters successfully grew plants in “Martian simulant soil.” What’s typically left out is that Martian simulant soil doesn’t precisely simulate Martian soil. At least not at the chemical level, since it doesn’t start with any perchlorates in it. Simulant soil is a particular product that captures some of the texture of Mars soil, but is really just Earth soil that is the closest match to what we think Mars soil would be. Nobody has ever grown a plant in Mars soil, but most likely, Mars dirt will require an involved process of cleansing and fertilizing and seeding with microbes, and even if it works out, we’ll need to validate that the plants themselves are safe for human consumption.

By the way, lighting will be a problem. For reasons we’ll discuss later, you probably can’t use glass as your exterior. If you’re on Mars, the light levels are already substantially lower than on Earth, and occasionally the sky is blotted out with dust. Likely you’re using an artificial light source, or perhaps piping light from the surface via fiber-optic cables, or both.

Just as with humans, we don’t know for sure how microgravity and space radiation will impact plants.  So much for gardening. Can we ranch? Cows are out. Pigs are out. Chickens are okay, but squirrel is better. In fact, why not hamsters? Because there’s a better option: insects. They reproduce quickly, don’t take up a lot of space, eat food scraps, are high in protein. Proposed bug-protein sources include crickets, silkworms, mealworms, hawkmoths, drugstore beetles, termites, and flies.

For a completely closed-loop ecology, we’d like as much as possible to be recycled: your breath, the moisture your body gives off, urine, feces, flaking skin cells, and whatever other effluvium is currently radiating from your mortal coil. In an orbital space station, you’d really want to get as close to 100 percent as possible. On the Moon or Mars there can be substantially more tolerance, though you’ll still have to be mindful about those elements that are hard to replace locally, such as carbon on the Moon or phosphorous on Mars, and nitrogen almost anywhere.

We don’t have a lot of experience with in-space recycling. The ISS is big for a space station, but likely far too small ever to have a self-contained ecosystem. We say likely because you’re never going to get anywhere close to the plant-to-human ratio of Earth with six people in such a small container. That said, it’d be quite valuable to know in principle how small you could take one of these systems. For the moment, we don’t know. Closed-loop ecologies are complicated and not a lot of money has gone into them.

The earliest experiments on humans in closed loops were the BIOS-1, 2, and 3 systems built in the USSR starting in 1965. They originally tried using pure algae to keep the men alive. In case you’ve forgotten high school biology, algae are basically plant sludge. They eat carbon dioxide, exhale oxygen, and are a nutritious source of calories if you don’t mind eating the same horrible meal every day forever. Later BIOS experiments introduced plants like wheat, beetroots, and vegetables, and ultimately were able to control CO2 at a reasonable level. A major problem they had, which will be quite relevant for space settlement, was that it took a lot of work—20 percent of the crew’s time was… Some highlights have been hidden or truncated due to export limits.

A near completely closed system would only be accomplished in the 1990s, and never duplicated afterward. Biosphere 2 is a 3.14-acre nearly airtight greenhouse in Arizona. It was born through a strange partnership between a billionaire and an enigmatic counterculture technologist group called the Synergists. They weren’t quite a cult, but they were at least, let’s say, cult-adjacent. This created issues. Their charismatic leader, John Allen, had space in mind when he designed Biosphere 2, but his training and crew-selection notions weren’t exactly NASA’s.  Socially, things didn’t go great. Early in their stay in Biosphere 2, the crew of eight began fighting, ultimately splitting into two hateful factions, each consisting of two women and two men. With more than a year to go, they were no longer on speaking terms. They stopped dining together or even making eye contact.

“Perhaps on Mars, with the safety of home at least forty-eight million miles away, we would have been able to pull together. But then again, perhaps not.  There were also problems with food.  The half-feral chickens they’d hoped would be especially robust had failed to lay eggs regularly, and the unusual breed of pigs they’d selected had been reluctant to eat scraps. Microbes attacked their crops, withering several high-protein high-calorie species. Ultimately, they were forced to eat unripe bananas and an unpalatable type of bean normally used to feed farm animals. The men lost about 18% of their body weight and the women about 10%.

The ecosystem suffered too. The designers of Biosphere 2’s ecology used a technique that may be used in space one day, called “species packing.” The idea is you start with a lot of species, many of which are ecologically redundant, on the assumption that some will be wiped out before balance is achieved. This indeed happened, but they ended up packing more than they intended. Proposals for space settlements sometimes note the possibility of precisely selecting what life forms come along with the project. In the one big experiment where this was tried, at least two stowaways came along: cockroaches and bark scorpions.

The biospherians also nearly lost control of the atmosphere. In a functioning closed loop, CO2 and O2 do a sort of dance as animals convert oxygen to carbon dioxide and plants do the reverse. But at one point the O2 started falling even as CO2 kept rising. This was not supposed to happen, and the crew became breathless and lethargic as they tried to do their work. What happened? The choice of high-organic-matter soil meant that microorganisms pulled a lot of oxygen out of the atmosphere, releasing CO2. Then, some of that CO2 was absorbed by structural concrete.

So why do we say it wasn’t a calamity? For one thing, it more or less worked. Eight people entered, eight left. The problems they had could have been rectified for future experiments simply by selecting better animals and modes of pest control. Some errors were downright trivial. Several high-calorie fruit trees like mango and avocado were simply not fruiting by the time the experiment began, but would have been for subsequent crews.

Assuming these problems could be solved, could the whole system have been ported to Mars? Nope. Most important, the structure would have to be changed. On Earth, the air pressure inside Biosphere 2 was relatively close to the pressure outside. Still, the system required two huge “lungs” to make sure the expansion and contraction of the atmosphere due to temperature change was accommodated. This will be trickier in the near vacuum of space. On the ISS, windows have four panes of glass each, the thinnest of which are a little over one and a quarter centimeters thick, and the thickest of which is over three centimeters. It may be possible to duplicate something like this over several acres in space, but it will not be cheap. A likely alternative will be to bury the whole thing underground, having regolith supply the outside pressure. But now you absolutely have to pipe in or generate light by some means.

That’s not great, but then again you’re likely going to heap regolith on your home anyway to deal with radiation.

Biosphere 2 would likely also require efficiency improvements to work on Mars. Remember, if you want bread inside the biosphere, you start with seeds planted in the ground. You have to grow wheat, take it to a threshing machine, grind the seeds, and then start the normal process of baking. If you’d like cheese on your toast, you’ll have to be a goatherd and a cheesemaker. Effectively, you’re subsistence farming on a tiny plot of land that sometimes requires technical system maintenance. The result in Biosphere 2 was an average workload of eight to ten hours a day, five and a half days a week. This is despite not doing all the chores of a space settlement, including running a power plant, doing construction, manufacturing, and more.

Kelly once talked to a group of researchers who work on closed-loop ecologies and asked them what they thought of Biosphere 2. A common view was that it was cool, but too ambitious. For the cost, which was around $300 to $400 million in today’s money, better science could’ve been accomplished using a series of small facilities, scaling up as you go.

There have been other, smaller-scale experiments since. For example, Japan’s Closed Ecology Experiment Facilities (CEEF), in which the system successfully supplied most of the food for two human “eco-nauts” as well as their goats. China operates the Lunar Permanent Astrobase Life-support Artificial Closed Ecosystem, or just the PALACE. The Lunar PALACE has had crews of three do partial seal-ins and had good success recycling water and clearing carbon dioxide out of the air with plants. None are nearly on the scale of Biosphere 2, which itself wasn’t nearly on the scale needed.

We would love to be able to share a more definitive science of, say, how to put 100 humans in a glass bubble and have them live indefinitely. We don’t have it.  Biosphere 2 cost around a tenth of a percent of the ISS. People can debate what the point of space stations is, but if they’re part of a project leading to human settlement off-world, this is not a good allocation of resources. For the same cost as the ISS, 500 biospheres could’ve been built.

A major reason governments pay to stick tiny habitats full of humans in orbit is national prestige—looking smart and strong in front of the world community. Blasting humans in a rocket to the Moon is substantially more impressive than creating a biosphere on Earth. It is not hyperbole to make the statement [that] if humans ever reside on the Moon, they will have to live like ants, earthworms or moles. The same is true for all round celestial bodies without a significant atmosphere or magnetic field—Mars included.

Humans are squishy and weak. The real estate options are toxic. And pointy. And cold. You’ll be growing vegetables in your own waste, tending your food bugs, and fighting off bark scorpions while drunk on beet wine. This is humanity’s new dawn.

Taking data from 2020, almost 60% of worldwide electricity comes from fossil fuels. Unless we discover something very surprising about Mars’s past, and then decide to set it on fire, anything with the word “fossil” in it is a nonstarter. Most renewables won’t work in space either. Hydropower requires flowing water. Wind power requires wind. Although there are, in fact, occasional proposals for Martian wind power, to make use of the ultrathin atmosphere the turbines would have to be huge. Geothermal energy, where heat is drawn from deep underground, won’t work on the geologically quiet Moon. It might work on Mars, but would be another enormous on-site construction project, and the best locations for geothermal power may not be the best locations for an early Mars habitat.

This leaves two options: solar power and nuclear power. If nuclear power makes you nervous, you’ll be tempted to go all in on photovoltaics. But consider what that would entail on the Moon or Mars. Typical Mars proposals for tiny crews call for acres of panels to be set up just for an initial foray, never mind running the vast underground greenhouse

If we assume Martians have power needs comparable to average US citizens, a Martian city of 1 million would require around 130 square kilometers of solar panels. Martians, however, will almost certainly require far more power given their need to do most of their farming and manufacturing locally.

On the Moon, unless you’re on the Peaks of Pretty-Much-Eternal Light, the panels will simply not work for two weeks at a time. On Mars, they’ll work during the day, but remember, the day is about half as bright as what you get on Earth.

In both settings, you’ll want battery banks for the dark periods. The total weight of batteries depends on the location and power needs, but at the very least we’re talking about thousands of tons of equipment, possibly quite a bit more. Even if you have these huge backup power systems, you can’t just plug in solar panels from the Home Depot. You have to have panels that can endure high levels of radiation, meteorite strikes, abrasive regolith, and unearthly hot-cold cycles.

A common response to this concern is to shout “Robots! By God, robots!” We like robots, but we are skeptical. A recent mission called Mars InSight made use of a tool called “the mole,” designed to drill five meters into the Martian surface. It managed two to three centimeters before failing, due to a combination of low friction and other factors. We’re a long way from an autonomous robotic system that can assemble, place, and maintain hundreds of acres of solar panels and farm land.

If you could magically transfer an insane quantity of plutonium-238 to Mars, it could be a very convenient way to get power—heat, electricity, and no risk of any of the classic nuclear fears like meltdowns or coolant leaks. But you can’t. These systems just don’t provide enough energy for the mass.

When people refer to a “nuclear reactor,” they’re usually talking about a fission reactor. The systems we talked about above are powered by radioactive material that, if you will, “naturally” decays. Nuclear fission reactors force atoms to decay rapidly. The result is a tremendous amount of power per mass. Fission reactors come with risks. Launching them comes with the danger of what aerospace engineers call “rapid unexpected disassembly,” better known as BOOM! Once they’re on-site, the main issue is that they emit radiation, so you’ll need to shield them, most likely by siting them far from your habitat and burying them in regolith. There is, of course, some additional risk of a nuclear meltdown, but let’s remember that Mars is already covered in toxic regolith so it’s not going to devastate the local watershed or whatever.

we’re sure some of you reading this book are still not reassured. We get it, but what we want you to understand is that saying no to nuclear power is basically closing the door on space settlement until some exotic future power sources are available.

The big picture here is that shielding will be difficult, and any artistic rendition of a space settlement where everything is under a glass dome is likely wrong. As space architect Brent Sherwood laments, writing about lunar architecture: “The image of miraculous, crystalline pressure domes scattered about planetary surfaces, affording a suburban populace with magnificent views of raw space, is a baseless, albeit persistent, modern icon. Such architecture would bake the inhabitants and their parklands in strong sunlight while poisoning them with space radiation at the same time.”

For now, if leaving Earth is humanity leaving the cradle, well, humanity is going straight to its neighbor’s basement. By now it should be clear why lava tubes will be so tempting. No need to pile up regolith if there’s a huge, probably stable hole just waiting for you. Plus, there shouldn’t be much dust, except around the entrance. So you just go in, blimp out an inflatable bouncy castle that only has to protect you from leaks and moderate temperature swings, and voilà.

The first woman who ever menstruated in space had problems with “leakage.” Remember, space is awful. There is no gravity to pull fluids in a generally downward direction. Blood, through a process called capillary action, tends to climb out. The astronaut elected to wear a tampon as well as a pad. Women astronauts today mostly favor hormonal birth control.  Ultimately women wore a version of what we now call a MAG: maximum absorbency garment. Basically, adult diapers. MAGs are now the standard clothing for situations like launch and landing, where astronauts can’t just get up to use the potty.

This is true for men as well, and it’s a blessing. In order to use the old system, men were required to specify whether they needed a small, medium, or large. The choice between being honest with the medical attendant and potentially wetting yourself while strapped in for launch was apparently Scylla and Charybdis for some.

Rockets have been military tools for millennia, going back to the discovery of gunpowder in China around two thousand years ago, and have been used by militaries around the world. However, for most of their history they weren’t a prominent feature in warfare. They were small, hard to control, and not very efficient at exploding enemies.