Moon: Industrial Complex

## Transcript

### Introduction

The Moon has beckoned to humanity throughout history, and it will soon be our ladder, extending our reach further into the cosmos. Today we’ll be looking at the Moon, and how it might in the century to come serve as a vital manufacturing and fuel refining depot and stepping stone. Interestingly though it’s biggest role in the near-term will likely be focused on the development of space closer to home, in orbit of Earth as the Moon is.

### Moon Benefits and Implication

To see why, we first need to ask what the Moon has to offer and how we will go about getting stuff off the Moon. That’s a key point because while the Moon has plenty of resources, it has little Earth does not have vastly more of. It’s also where all our stuff is, including our factories and scientists and engineers and everyone else. This would lead many to think we really have no interest in the Moon and is one reason folks often suggesting bypassing it in favor of Mars or other planets. And yet the biggest problem with Earth is that it has so much stuff—as in, mass.

All that mass generates a gravity well you have to claw your way out of to get into space. It also means there’s a thick atmosphere clinging to our world that makes it even harder to launch things, though easier to land stuff, much easier actually than on the Moon. The Moon has no atmosphere to slow ships or cargoes down as they approach. It also has surface gravity barely a seventh of Earth’s, and an escape velocity of just 2400 meters per second or 5400 miles per hour. Quite fast but barely a fifth of Earth’s, and it takes less than a fifth as much fuel to lift something off it. Gravity wells are not your friend in space but they get far worse as we pile mass on. A rocket using a liquid hydrogen fuel to escape Earth might need 12 tons of fuel to get a given payload away. Whereas on the Moon it would only require .7 tons to to get it off the Moon. It would be even cheaper in terms of not needing anything like all the extra mass and equipment needed to get that spacecraft off Earth reliably and safely, like fairings, those protective nose cones on rockets for plowing through the air, which of course the Moon lacks.

Of course there’s precious little hydrogen on the Moon, and it’s mostly tied up in water-ice which we probably want to use for other things, and there’s obviously no ready supplies of kerosene or other hydrocarbon fuel types either. So we’ll need to consider other types of fuels, and for that matter if we even want to use fuels or opt instead for alternatives like a lunar space elevator or a mass driver. Space Elevators are nice in that they don’t require much power to operate, but they do take some and have other problems we’ll get to in a bit. Making chemical fuel or running a mass driver of the electromagnetic catapult or rail gun variety both are energy hogs, and so we’ll need to ask how we’ll go about getting power on the Moon, all of which we’ll also get to in a bit. There are vast amounts of Silicon, Oxygen, Aluminum, and Iron on the Moon and those last three can be used to make good fuels. Of course you mostly need fuel to get stuff off the Moon, so let’s ask what the Moon offers us that we want to take away from it and where we want to take it.

#### Agriculture and Space Farms

Fiction often shows us moon bases but tend to be a bit unclear on what they’re really for, and what they’re not for is growing food. At least not for exporting. You might grow food on the Moon for local consumption, as opposed to bringing it from Earth, but you’d probably only use it for feeding folks in space during the earliest days and you just happened to find it easier to expand local production a bit rather than setting up space farms. We’ll examine that more in the upcoming episode “Moon: Crater Cities.”

Part of the problem though is that the Moon has really long days, a month long, half of which is night which is a long time for plants to go without illumination. What light it gets is also harsh, not filtered by an atmosphere removing the frequencies more harmful to plants and equipment. You could grow food there, but either need to provide supplemental lighting or pick species that are adapted to handle darkness for long periods. You probably need to provide shading too, as many plants wouldn’t fare well in two weeks of perpetual noon-time sun.

All-in-all, it makes more sense to use large rotating habitats in orbit for food growth instead, especially as these can be made vastly cheaper than those rotating habitats meant for people to live in, such as the O’Neill Cylinder, and we’ll be discussing those and life inside them in a couple weeks. Of course you probably do want to grow food there initially, not to mention source your rock, air, water, and equipment for those space farms from the moon, where you can. Some plants you may want to grow locally for aesthetics or as specialty fresh foods, like fruit trees or herbs. These plants may also be used to recycle waste products of the colonists.

If you are growing food on the moon you need power for artificial lighting or rather significant usage of orbital mirrors to send light down, which is certainly doable and we may as well begin our discussion of power with solar as an option. We’ve got three ways we can use sunlight and three places to obtain it from. We can use it for plants or other processes that directly make use of light, like a solar kiln for smelting metal or rock, or we can use it for power generation, either solar thermal or photoelectric. Photoelectric being the solar panels we’re used to, while solar thermal is where you use the concentrated sunlight to heat something and run a standing heat engine, such as a steam turbine, like we use in conventional power plants.

Solar panels are a bit problematic on the Moon because you have that two-week dark phase, though they don’t have to worry about cloudy weather and there are many craters whose rims experience longer daylight periods. Indeed one of the proposed methods to maximize the exposure of solar panels is to hang them like curtains from tall towers, following the sun, extending the daylight as the sun sets. For the same reason, polar craters are also logical base locations due to the extremely long daylight possible on their crater rims and from the ice we hope to find at their eternally dark bottoms. And again we’ll look at that more in Crater Cities.

On the photosynthesis side of things, those extended light periods experienced on crater rims might be sufficient to allow plants there to remain healthy as opposed to two full weeks of darkness, and would at least cut down on supplemental lighting. These are good spots for initial space farming though obviously are in a limited supply. Eventually, a lunar industrial complex will be producing so much power for metals refining, chemical processing, and manufacturing that a few small farms worth of LED lights won’t really amount to much in your power budget.

But in the end the vast majority of food production will be done on large factory farms and food processing facilities in space once the cost of landing a shipment of groceries is less than your local cost. Similar to how you might have an orange tree or small garden, but your not locally sourcing a cake recipe.

#### Energy: Solar

But back to solar panels, modern, efficient ones are rather hard and expensive to fabricate locally from ISRU, or in situ resource utilization, the term used for basically living off the land. Though that might get far easier down the road, the raw sunlight, heavy on ultraviolet, and damaging moon dust and micrometeorites, might be rather rough on such panels. There are designs for less-efficient, simple solar panels made from ISRU materials that can almost be paved on the lunar surface. The problem with these is that they need to be cleaned of lunar dust frequently if they are to be located anywhere near a mining base or rocket landing pad. They are also fixed so they can’t follow the sun, and because there is no atmosphere to refract or reflect the sunlight like on Earth, this further reduces their efficiency. Fabricating more rugged or structural ISRU solar panels, such as those we discussed hanging like curtains, will take more resources and cost more, but would allow sun-following. Lastly, while concentrated solar may allow better use of your solar panels, they can have thermal management problems in space, further adding to their cost and complexity. Adding to solar power’s short-comings is the limitation of battery capacity to function through the night, away from the poles.

Solar thermal on the other hand is particularly nice on the moon because big mirrors and parabolic dishes are easily fabricated, they can just be shiny bits of aluminum or iron, neither in short supply on the moon. Additionally, there’s no air, and heat can only be lost via radiation, convection, and conduction, so you can turn your mirrors onto giant blocks of basalt – which is plentiful on the moon and a great medium for heat storage and they won’t cool off as much at night as it’s just the vacuum above them, not air or water also acting as a coolant by convection. This is especially true if we cut blocks of basalt and basically stick them in a thermos, vacuum on all sides. So no convective losses from the vacuum and only minor conductive losses in the thermos and radiative losses can be minimized with a reflective barrier. Quite the thermal battery. That’s a bit sophisticated, so early on you might just use a chunk of basalt up off the ground on insulating feet to minimize heat loss to conduction, or in a pit where you kept a bowl up on feet and filled it with gravel. You can even skip that for focusing light on a big chunk of basalt but you’d lose more heat to conduction into the neighboring rock.

We call this approach a Thermal Wadi, as opposed to Wadis in the desert, dry spots that fill with water in the rainy season, in this case we fill them with light and heat in the sunny season, every month. Now we can attach those blocks to a heat engine and have a nice power supply when the sun goes down. Needless to say, you can also use these to keep bases warm when the sun goes down, or for that matter cold when the sun is up. You can also be using solar kilns in this role as well as their role of melting down metal or rock, and solar kilns work better on the moon from the lack of atmosphere anyway.

Using these approaches lets you avoid needing to have a month-long production cycle that is on during the day and off during the night, or at least lets you avoid a total shut down at night, though we often do long on and off production cycles in some industries, such as metal smelting, here on Earth, and could on the Moon if we needed to, and we might early on as we need to start very simple. It’s not very hard then, with some fairly basic infrastructure, to get major metal production going on the moon and it can be massively scaled up. You benefit a lot from having clever robots do the work rather than people but you don’t actually have to live on the Moon to work there. The signal lag time from Earth is just a heartbeat or two, enough time to be noticeable and irritating but close enough to allow remote control of facilities and robots.

Now I said there were three basic ways we could use sunlight but also three places we could get it from. The first is obviously the surface of the Moon, and the second would be advanced power production by nuclear fusion, where sunlight comes from in the first place, but while we’ll be looking at nuclear fission as a power source and ship drive today, we’ll skip fusion as a topic we’ve covered more elsewhere. (Fusion Power)

Our third way is just to remember that the Moon has very little gravity and no atmosphere. That makes producing power satellites or mirrors and getting them into orbit a good deal easier, and it would not be hard to coordinate those to get power or light to places when it was dark outside, scaled up enough you could even create a 24 hour day cycle but we’ll skip that for today. See the Power Satellites episode or Winter on Venus for more discussion of those topics.

#### Megastructures and Launch Assist Methods

However, while putting stuff in orbit of the Moon isn’t too hard, that low gravity and lack of wind makes it very easy to erect massive structures. I mentioned those tall towers and putting our solar panels on them. Building some super-high, strong, and skinny tower on the Moon is very easy. Indeed it is so easy that we can build a space elevator on the Moon out of existing materials, not needing the very strong materials like Graphene and Carbon Nanotubes an Earth Elevator would take.

Sounds like a great idea but there is one problem, the Earth. The Moon perturbs the orbits of objects around the Earth somewhat. But the Earth has 81 times the mass of the Moon, and it perturbs orbits around the Moon a lot. If you were to build an elevator on Earth, you’d put its center of mass in a geostationary orbit. That’s where it will orbit the planet at the same rate the planet turns, so it will stay directly above your chosen spot on the equator. The altitude of a geostationary orbit is about 1/10 of the way to the Moon, so the Moon’s gravity does perturbs the orbit some but only to a degree we can manage and compensate for. If the Moon had a nice short day like we do, it would work about the same there. But the Moon is tidally locked to Earth, so its day is a month long, and a luna-stationary orbit would have to be a month long as well. That means it would have to orbit the Moon at an altitude that takes it 1/4 of the way back to the Earth, a distance where the Earth actually exerts far more force on your satellite than the Moon does. There is the L1 Lagrange point between the Earth and Moon, where the forces exactly balance each other, and it’s only about 1/7 of the way back to the Earth. The problem is, it’s not stable. If your satellite drifts off the Earth-Moon axis, gravity will pull it back, but if it drifts either way along that axis, it will start falling toward whichever body it’s now closer to. The L2 Lagrange point above the far side of the Moon is similarly unstable. The only stable Lagrange points, where you could put a satellite in a true luna-stationary orbit, are the L4 and L5 points that respectively lead and lag the Moon in orbit around the Earth. Unfortunately, those are actually as far from the Moon as the Earth is—not very helpful when you’re trying to build an elevator. Now again neither is stable either, and while we can use some of the tricks we discussed in Space Elevators, like multiple tethers reaching up at angles to a common terminus, and also have some options for polar elevators, it’s not a great option.

Sky hooks, also known as rotavators, work a bit better since without an atmosphere and with a lower gravity and orbital speeds you can have one swing right down and snag something off the ground.

We looked at those in detail in early episodes of our Upward Bound series, and followed them up with a device called a mass driver, think giant space gun. Those can work on Earth but are problematic because you need to reach higher speeds and you have to use an entirely enclosed runway or barrel to keep the air out and also have to have the muzzle sticking up tens of kilometers above the ground to avoid your vehicle slamming out of the barrel into the atmosphere at re-entry speeds. Needless to say, it’s also quite an engineering feet to build a tower tall enough to hold that muzzle up. That is far easier on the moon, what with the low gravity and lack of wind in the atmosphere shoving on that tower, but you don’t need to bother because there’s no atmosphere you need to get above. You can just run a long metal track on the ground to build up speed and let go once you hit orbital speed. All of those are options that work on the Moon, and the mass driver is probably the easiest and best for most applications, but you might not even bother since again, it doesn’t take too much fuel to get stuff off the Moon and as we’ll get to in a moment, that’s likely to be the main industrial production of the Moon, or one of the big ones anyway.

I should note though that landing stuff on the Moon is a good deal trickier if you want to avoid using rockets, there’s no air to help you slow down. Trying to rely on sheer friction, like a runway, is not a good idea since you’re still moving very fast and safely coordinating that would be dubious. The skyhooks are nice options for slowing down, the elevator too, and one could potentially harpoon a ship like we discussed in Colonizing Ceres or even use some corridor runway filled with low-density gas for breaking,

#### Resource Extraction/Economy

Of course fuel works pretty well and I did mention that would be a big export. You can make fuel out of water, with enough power, you just break it down into hydrogen and oxygen then burn those as your fuels, but we don’t know how much water-ice is on the moon and we probably don’t want to be using that up, so it might work okay in the early days as a short term fuel but not something we will use in the long term.

2

Al

(
s
)

Fe

2

O

3

(
s
)

⟶
2

Fe

(
s
)

Al

2

O

3

(
s
)

{\displaystyle \ce{2 Al(s) + Fe\_2O\_3(s) -> 2 Fe(s) + Al\_2O\_3(s)}}

We will need to use common lunar ISRU materials and first among those available is oxygen, of which the moon is roughly 40% by mass, and it will practically be a waste product of our industrial activities, as things like iron and aluminum will be found as oxides we need to separate to get the pure metal. ALICE, Aluminum-Ice rockets, using nano-aluminum powder and water ice are tempting but again it uses up water, or more specifically hydrogen, not ideal for heavy space usage. But we can use aluminum and liquid oxygen as a monopropellant gel or as a bi-propellant, and also aluminum, iron, and oxygen, also known as thermite, and of course Magnesium, which also has a very energetic reaction with oxygen, is readily available on the moon.

None of these is exactly ideal as a main ship propellant, though they do work well enough and work very well for things like station-keeping and orbital maneuvering, which is going to be the biggest fuel usage in a robust Cis-Lunar Economy, where most of the ships will be moving around Earth-Moon orbital space and which will probably be collecting a growing number of space habitats, power stations, factories, farms and so on as time rolls on.

The Moon however is also rich in uranium and thorium, and noticeably lacking in delicate ecologies, so it’s a great place to build fission reactors as well as radioisotope thermal generators, RTGs, one of our favorite electric supplies for spacecraft. You can also build some disgustingly simple nuclear rocket drives that, while filthy as heck, enough that it would probably be a war crime to use them in Earth’s atmosphere or low-orbit, do well enough in deep space or on the Moon. Nuclear makes a nice power supply for those dark weeks on a moon base and RTGs, mostly made of radioisotopes like Strontium-90 or Plutonium-238, would make excellent power supplies for spaceships and satellites and moon rovers where solar wasn’t a good option.

Of course we also have the RTT, Radioisotope Thermal Thruster, which differs from an RTG somewhat. An RTG uses thermocouples to turn the radioactive heat decay into electricity. They are very durable and reliable with no moving parts to break or wear down, and are easy to build, though very inefficient at conversion, usually under 10%. The RTT, or Poodle Thruster, is the same; it just uses that heat to produce rocket thrust instead. These unfortunately can not be throttled in their thermal power output, RTGs and RTTs produce a constant power supply, though by changing how much propellant you use you can throttle your thrust, though it slowly weakens as the material decays, dropping to half after one half life. And of course you have all that lunar oxygen you can use for propellant. This is also not bad for station keeping or objects that run back and forth constantly, like a shuttle between the Moon’s orbital Station and Earth’s, assuming anyone lets you bring it near Earth, though they’re not too dangerous if one gets wrecked and crashes on Earth and aren’t ideal bomb material either.

We’ve never truly had a nuclear economy on Earth, even in those places where fission makes up a large part of the power generation, so it’s a bit hard to really state how much of an industrial engine that is. The Moon, and space in general, is already a radiation nightmare so being able to run massive nuclear torch drive ships and atomic-powered foundries, smelters, and mass-drivers is a big deal. If you go all in on that you can start turning out aluminum and steel at ridiculous outputs, and that gives you the massive construction capacity you need for building up a true space infrastructure. Safety really is not an issue, but we already detailed non-atomic options like solar kilns if we need them instead. Nuclear is more attractive in many regards and could turn the Moon into an Industrial Nuclear Juggernaut.

So that covers fuel. Fuel for station-keeping and running around the Cis-Lunar volume of space. But fuel, be it chemical fuels like Aluminum or nuclear rockets, that can also be used for running ships back and forth to Mars or the Asteroid Belt or even out to the icy moons of the gas giants to retrieve ice for water and fuel if the Moon doesn’t have enough. Oxygen too, the Moon has plenty of it, but not so much nitrogen or carbon and plants need those too, and these are elements you can find plentifully out deeper in space, in the form of Nitrogen gas, ammonia-ice and methane. Methane and ammonia are nice stable sources of hydrogen, and methane is 25% hydrogen by mass and ammonia is 18%, while water is only 11%, and the remainder is oxygen, which is beyond plentiful on the Moon and as mentioned likely to be a waste product of many of our other activities there.

Hydrogen is a critical item for good space travel as it’s our best propellant, so with it being rare on the Moon and hard to get off Earth, your first big supply chain is to get hydrogen back to the Moon. It’s easier to think gas giants, but actually getting hydrogen off them is no mean feat, and raw hydrogen is not easy to transport, so methane is your preferred source, off icy bodies, and water and ammonia your nominal runners up, needless to say both are very handy for other things too. Comets are also nice sources for those.

We’re trying to keep ourselves pretty low-tech and near term in this episode, so we’re focused on the stuff that’s easier to do now in terms of both existing technology and easy deployment, see Industrializing the Moon or Battle for the Moon for some of the more high-tech scenarios.

But whether you’re running out to the rim of the Asteroid Belt beyond the frost-line or to the Moons of Jupiter or Saturn, that gives us some nice imports. Hydrogen, carbon and nitrogen for fuel and food production, plus all those nice metal ores that are available in the asteroid belt and in the less mentioned but no less valuable hoard of tiny moons and asteroids around those two huge planets.

You can send crews out to those and setup bases, but extracting ices, water, methane, or ammonia, is a very easy bulk extraction process that can probably be done by fairly dumb machines with just a few nudges by controllers acting remotely from a light hour away, and those Poodle Thrusters make a very nice ship drive and power source for those kind of remote operations too. Poodle Thrusters do need refilling on propellant so are good for ice mining, where they can re-stock, and I can well imagine the Moon mass producing some sort of small probes that fly out to those icy bodies to survey them, latch onto patches of ice to refuel on propellant and drill samples, and wandered off to the next target, with bigger collectors following up for extraction.

Fundamentally the Moon is a great source for anything that we want in space in larger bulk quantities, like metal, but it’s also nice for things like Rare Earth Elements that are often rather rough to get economically on Earth while also being environmentally friendly, which is fine on the Moon where there’s no environment to befriend. Not a bad place to get phosphorus either, something we have a supply problem with here on Earth, and it should be noted that while it takes a lot of fuel and money to get off Earth, getting home is easy and cheap, so you probably can export stuff that isn’t precious metals home to Earth. It’s got precious metals too. It’s easy to forget when discussing asteroid mining and coming home with trillion dollar rocks full of gold and platinum that the Moon considerably outmasses the entire asteroid belt and has more of every metal than it does, albeit sometimes harder to extract.

But ‘hard’ is a relative concept and all those wonderful craters and lavatubes make nice bases to hide from micrometeors and the Sun’s blistering radiation, and that proximity to Earth allows remote control of any device and rapid extraction or evacuation of personnel back to Earth in emergencies, or sending in search and rescue teams. Out on Mars or in the Asteroid belt, you’re in deep trouble if anything goes wrong, because no one is coming and even advice and suggestions by radio will take an hour to reach you, not a couple seconds. For this reason and many more, the Moon is a great place to be building up our industrial might for space. Maybe not an ideal place to live though, and we’ll discuss some options for that in a couple weeks.

### Outro

So as I mentioned, we’ll be returning to the Moon in a few weeks to take a look at Crater Cities, but before then we’ll ask the big question of why life exists next week. We also talked a lot today about how the Moon might come to be a major colony one day, but would most likely be powering that growth by providing the raw materials to build vast number of habitats in orbit of Earth, in immense space stations such as the O’Neill Cylinder, and in two weeks we’ll take a look at what’s it’s like to be a resident of one of them, in “Life on Board an O’Neill Cylinder”. For alerts when those and other episodes come out, make sure to subscribe to the channel and hit the notifications bell. And if you enjoyed this episode, hit the like button and share it with others. And if you’d like to support future episodes, visit our website, IsaacArthur.net, to donate to the channel or check out some of the awesome SFIA merchandise.

Until next time, thanks for watching, and have a Great Week!