The Logistics of Going "Interplanetary": What Does It Take to Live on the Moon?
Welcome back to our ongoing "Interplanetary" series. In our previous installments, we looked at how humans might someday establish mobile and polar settlements on Mercury and floating cities on Venus. Today, we examine how humanity may one day establish a permanent presence on its only satellite - the Moon!
"Welcome to Tycho, your one-stop vacation destination for shopping, gaming, and lunar excursions! The time is 09:30 AM UTC, and the Earth is shining brightly through the main window. We invite you all to enjoy the view as you await clearance from customs and biochecks. We remind everyone to have their ID and the results of their latest biometrics on hand.
Those who are visiting for the first time, we recommend you prepare for the experience of a lifetime. In our fair city, you will be treated to sumptuous dining experiences, sleep in five-star hotels, and be free to relax and play in our premiere spas, gambling establishments, and live-action theatres.
And you'll experience all of it in the comfort of lunar gravity. You'll feel like your floating on a cloud. And we recommend you take the time to visit one of our many aeries and rent a pair of wings. Experience what it is like to soar before returning home to your 'grounded' existence!
For those who have signed up for our adventure package, be prepared to visit some truly historic places! In addition to a guided tour of the Lunar Museum, you will visit the Yuègōng, Mesyats, and International Lunar Village facilities. These historic locations are where the first humans lived and worked on the Moon. Today, the lunar population grows to one million during the 'high-season.'
Those who have signed up for our Grand Tour package will also get to see the Apollo, Artemis, and Zorya landing sites. We remind you that all patrons participating in extra-vehicular activities (EVAs) must remain with the tour guide and not enter these 'heritage zones.' The history of the Moon and its environmental integrity is our collective responsibility.
This season, we are honored and privileged to announce that the Wu Gang and Chaandr landing sites have also been added to the tour! We thank our colleagues at the Chinese and Indian consulates for their cooperation in opening these sites to us! Please exercise the same caution there that you would at the American and Russian landing sites.
We encourage our guests to make liberal use of the electrolyzer suites. Even if you haven't ventured out onto the surface with a guided tour, electrolyzer discipline is key to ensuring the respiratory health of yourself and others.
Spend some time with us, and we're sure you'll agree: the Moon is the 'common heritage' and province of all humanity. Let's keep it clean, safe, and enjoyable for all!"
To one day establish a permanent human presence on the Moon! An outpost of our civilization, where humans live, work, conduct vital research, and even spend their vacation days. A place where a new generation of humans are born, possibly called "Lunites," "Lunans," "Selenians," or "Apollonians" (Who are we kidding? They'll be called "Loonies"!)
Sure, it's something we've all heard about and read about, especially in recent years! It's been the stuff of science fiction for more than a century and something that inevitably comes up whenever space agencies start talking about their plans for lunar exploration. But compared to other concepts for establishing settlements beyond Earth, a lunar settlement is especially feasible.
This is not to say that there aren't some monumental challenges involved. But as Earth's closest celestial neighbor and the only body beyond Earth that has been visited by humanity, a lunar settlement could be accomplished before similar settlements exist on Mars, Venus, in the Asteroid Belt, the Earth-Sun Lagrange Points, or elsewhere.
Establishing a foothold on the Moon would assist in the creation of settlements on these other bodies considerably. With refueling depots and refurbishing facilities on (and in orbit around) the Moon, space agencies and commercial space companies could shave billions off the cost of deep-space missions.
And in the meantime, a settlement could be built around this infrastructure that would allow for lunar living, lunar tourism, and trade between the Earth and the Moon. It could be done. It just won't be cheap or easy. Some serious hazards will exist long after a lunar settlement is established.
First and foremost, the Moon has virtually no atmosphere to speak of. While there is a tenuous wisp that is the result of outgassing from the interior, it is so thin that it's close to vacuum. This means that there is a) no air to breathe, b) extremes in temperature, c) no radiation protection, and d) regular bombardment by meteors and micrometeorites.
To get a sense of what that is like, the Moon's tenuous atmosphere is composed of helium, argon, neon, sodium, and the surface pressure ranges from around 3 x 10-7 pascals (Pa) in the day to 3 x 10-10 Pa at night. Compare this to Earth's fluffy atmosphere, composed of nitrogen and oxygen (78:21) and averages 101.325 kilopascals (kPa) at sea level.
For this reason, the Moon is designated an "airless body." What's more, the temperature variations are extreme, depending on the time of day and the location. Around the equator, temperatures range from around -173 °C (-280°F) in the shadows and at night, to about 117 °C (243 °F) in direct sunlight. Around the poles, temperatures are more consistent, ranging from -123 °C (-190 °F) to -43.15 °C (-45.67 °F).
The lunar surface is also exposed to a considerable amount of radiation in the form of solar and cosmic rays. Based on measurements taken by China's Chang'e-4 mission, scientists estimate that the Moon's surface is subjected to an average of 316.8 millisieverts (mSv) a day. On Earth, people living in developed nations are exposed to an average of 3.1 mSv a year — 1/100th the amount!
On average, Earth is hit by 36.5 tons (33 metric tons) of meteoroids every day. But thanks to our dense atmosphere, the vast majority of these burn up high in the atmosphere and don't even make it to the surface. The Moon has no such protection, which means the surface is bombarded daily by thousands of objects that are a few feet to a few microns in diameter.
These rocks hit the lunar surface at speeds ranging from 12.4 mi/s (20 km/s) to 45 mi/s (72 km/s). At these speeds, even a relatively small object with a mass of 10 lbs (4.5 kg) can displace as much as 82.5 tons (75 metric tons) of lunar soil and rock and leave an impact crater that measures 30 ft (9 m) in diameter.
These impacts and the lack of an atmosphere are why most of the Moon's surface is covered in a fine powder known alternately as "moondust" or regolith. This fine dust is jagged thanks to the complete absence of wind and rain-driven erosion, making it absolute hell for instruments and machinery operating on the surface.
Last but not least, it's electrostatically charged, which means it sticks to everything! The Apollo astronauts noted that regolith brought back into the Apollo modules would adhere to surfaces and could not be removed, despite their best efforts. This dust is also known to have a detrimental effect on respiratory health.
Because it is in synchronous rotation with the Earth, the Moon is "tidally-locked" with Earth. This means that it has the same rotational period as its orbital period around a partner, and so the same side is always pointed towards the Earth. For people living on the lunar surface around the equator, the same part of Earth would constantly be visible in the sky.
Between tidal-locking and the fact that the Moon takes about 28 days to complete an orbit of Earth, this means that a lunar day and night both last the equivalent of about 14 Earth days. During the daytime, temperatures on the surface will reach a boiling 117 °C (243 °F) for two weeks, followed by fourteen days of a freezing low of -173 °C (-280°F).
A solution to this is to remain near the poles which contain places that, because of the moon's tilt, are exposed to less sunlight and where temperatures are consistently in the sub-zero range.
Temperatures are especially low in the permanently-shadowed craters that dot the region, which act as "cold sinks" that allow water ice to remain stable. The Diviner instrument on NASA's Lunar Reconnaissance Orbiter measured temperatures of -396°F (-238°C) in craters at the southern pole and -413°F (-247°C) in a crater at the northern pole.
Moondust to the rescue?
To recap, habitats on the lunar surface will need to be protected against radiation, the elements, and meteoric impacts. They will also need to be airtight, pressurized, and provide and a steady supply of air, water, and (as much as possible) food and supplies using only locally-harvested resources.
Hence, NASA, the European Space Agency (ESA), and other space agencies are investigating additive manufacturing (3-D printing) techniques that would use lunar regolith to fashion building materials on-site, rather than having to transport heavy materials from Earth. There are two ways to do this, both of which have been demonstrated here on Earth.
One method is to combine regolith with a bonding agent to create lunar concrete (aka. "lunarcrete"), which can be printed out to build structures. In terms of benefits, lunarcrete requires less energy to produce than other building materials, is unaffected by extreme variations in temperature, absorbs harmful radiation, and is unaffected by prolonged exposure to vacuum.
In 2018, the ESA conducted a demonstration where they 3-D printed a 1.65 ton (1.5 metric tons) block of lunarcrete using simulated regolith. Similarly, NASA has been researching "sintering technology," where regolith is bombarded with microwaves to create a molten ceramic that is then 3-D printed out to form the protective outer layers of a habitat.
These methods were featured in the ESA's proposal for an International Moon Village and NASA's SinterHab base concept — which have since evolved into the Moon Village and the Artemis Base Camp, respectively. Other concepts involve covering habitats in layers of regolith or building them so that most of the structure is underground.
Inflatable structures could then be deployed inside these larger structures and pressurized with nitrogen and oxygen gas. This is currently what the ESA has planned with their Moon Village concept, which calls for a series of semi-inflatable shell structures. This concept is similar to the Bigelow Expandable Activity Module (BEAM) currently attached to the ISS.
Regolith can also be used to manufacture propellant and oxygen gas (O2) since it's approximately 45% oxygen by content (as oxidized minerals). Here on Earth, the electrolysis method is used to separate oxygen from minerals, which creates oxygen as a byproduct. Recent research estimates that there is enough oxygen in the Moon's top layer alone to sustain 16 billion people for 50,000 years!
Liquid oxygen (LOX) is also a key ingredient in rocket propellant, the other being liquid hydrogen, methane, or various other hydrocarbons.
Water and power
As noted earlier, water ice exists in the permanently-shadowed craters around the Moon's southern polar region. For this reason, NASA, the ESA, China, and Russia all plan to build their future lunar bases in places like the Shackleton and other craters. At present, it's unclear how much water ice exists in the region due to it forming layered deposits that reach underground.
But based on the remote observations by radar instruments conducted by India's Chandrayaan-1 and NASA's Lunar Reconnaissance Orbiter (LRO), the lunar poles are estimated to have over 600 million tons (544 million metric tons) of water ice. That's enough water to keep a megalopolis like New York City supplied for the next 440 years!
Water can also be used to create rocket propellant since it's composed of hydrogen and oxygen, which make LOX and hydrogen fuel. Oxygen gas can also be produced by chemical disassociation, which happens naturally when water is exposed to sunlight (a process known as photolysis).
Given the abundance of oxygen in the lunar regolith, the Moon's ice will likely be used for drinking, sanitation, and irrigation. Herein lies another important aspect of a lunar outpost: the ability to grow enough food locally to lessen dependence on Earth. The potential for greenhouses in space and growing food in modified lunar soil are the subject of ongoing research aboard the ISS.
As for electricity, something which a lunar base and operations cannot function without, there are several plans in place. Existing proposals for lunar outposts all call for the positioning of solar cells around the craters' rim. These would provide ample solar energy, but other methods (used in tandem) are also being investigated.
For example, in recent years, NASA has been looking into compact nuclear reactors for use on the Moon. This began with the Kilopower project, which has since matured to become the Fission Surface Power (FSB) concept. This proposed system calls for a reactor that can continuously supply 40 kilowatts (kW) power for ten years.
China is also researching nuclear reactors for the sake of future space exploration. According to recent news, they have (allegedly) completed work on a considerably more powerful reactor than NASA's FSB concept.
The curse of low-g
Alas, there is still the matter of lunar gravity, which is roughly 16.5% (0.165 g) percent of what we experience here on Earth. According to ongoing research conducted by NASA and other space agencies aboard the International Space Station (ISS), prolonged periods spent in microgravity environments have long-term detrimental effects on human health and physiology.
The most comprehensive study to date is the NASA Twins Study, which relied on twin astronauts — Scott and Mark Kelly — to assess the effects of spending more than a year in space vs. a year on Earth. According to the results published in April 2019, Scott Kelly's time in space resulted in muscle and bone degeneration and changes to his cardiovascular health, organ function, eyesight, and gene expression.
Readjustment to Earth gravity was also an ordeal for Scott Kelly, who chronicled the experience in the book Endurance. While experimental evidence in low-g is lacking, it is logical to assume that they will be similar to the effects of microgravity. Therefore, lunar astronauts and future generations living on the Moon must follow a strict health regimen.
For astronauts aboard the ISS, this consists of daily exercise and resistance training to ensure cardiovascular health and to maintain muscle and bone density. Paired with regular health checks, supplements, a healthy diet, and possible biomedical intervention, future "Loonies" could lead healthy lives on the Moon.
Another possibility is to construct rotating facilities in orbit that simulate gravity. Commercial space companies like The Gateway Foundation are working towards such a station in Earth orbit. The design consists of two rings (an inner and outer ring) that provide different levels of simulated gravity based on their distance from the center (the Hub).
The Lunar Gravity Area (LGA), located closer to the Hub, would rotate at a slower velocity to create the sensation of lunar gravity (0.165 g). The Martian Gravity Area (MGA), as the outer ring of the station, would rotate much faster, to simulate Martian gravity (0.38 g). A similar facility could be built in orbit of the Moon to gradually acclimate people returning to Earth.
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Put simply, an outpost (or outposts) on the Moon could benefit humanity in numerous ways. It would allow for regular access to the lunar surface, enable vital research into low-gravity and its effects on terrestrial organisms, and shave billions off of the cost of missions destined for Mars and other locations in deep space.
Beyond the scientific and spaceflight-related, a lunar outpost would also allow for the creation of new industries, such as lunar mining, space-based solar power, commercial space stations, and lunar tourism. The infrastructure created for this purpose could also lead to a thriving economy in the Earth-Moon system, including asteroid mining and space-based manufacturing.
The Moon is our gateway to the rest of the Solar System and the first step in any plan for "going interplanetary." Granted, the challenges are enormous, and the cost of developing all this architecture is nothing short of immense. But as the Loonies say, "TANSTAAFL!"
"From all of us here at Tycho and our partner facilities at Yuègōng, Mesyats, and the Lunar Village, we thank you for spending time with us here on the Moon. We wish you safe travels as you make your way back to the Earth-Moon Gateway, where you will spend the next few weeks in luxury and comfort as you reacclimate to Earth-normal gravity.
"For countless generations, humans have looked up in awe at the Moon. Today, over ten thousand people live and work here year round. But when the 'high season' occurs, we are happy to receive many, MANY more! The Moon is the collective heritage of humanity, and it is therefore appropriate that we enjoy it together."