This infrastructure does not simply serve to build a single space settlement—it is unlikely that every bit spent on space will go to a single, risky project. If the space settlement project were to not succeed, parts of the infrastructure would likely go to waste. Therefore, our infrastructure should be on itself successful, in order to decrease the risks involved with investment.
The Moon, mere days away from the Earth, provides much of the material needed for a space settlement, and provides it with a fraction of the propellant required to lift material from the Earth. The Moon has significant concentrations of Titanium, while asteroids have very low concentrations, true of Aluminum as well (Crawford, 2014). Titanium is prized for its low-mass, yet high strength properties for aerospace applications. As asteroids cannot supply certain important resources, a base will be constructed on the Moon in order to provide space settlements resources and generate profit.
Two locations have been selected for building bases. The first is the craters in the Lunar polar regions. 600 million metric tons of water ice is estimated to be locked up in the north pole alone (Ambrose, 2014). If utilizable, we gain access to one of the most important space resources. When electrolyzed, water is broken down into oxygen and hydrogen, together the most potent chemical rocket widely used, and hydrogen is one of the best propellants for NTRs. Oxygen is critical for use in habitation, as it is the gas required for all humans to survive. In its pure form, water is key for hydroponics and drinking, which is key to ensuring a stable and self-reliant space settlement free from constant, expensive resupply from Earth, which is subject to delays. Water can also be used for radiation shielding, which can double as reserve tanks.
The polar regions also offer the peaks of eternal light—these are areas that are lit by the Sun permanently with the exception of solar eclipses, allowing solar power to be the main supplier of power, whereas another power source like a nuclear power plant would have to be used in most locations, which encounter darkness for 2 weeks. No place has been found that is permanently illuminated, but some are lit for as much as 94% of the time, which is likely enough for solar power to work, given energy storage (Bussey, et. al 2010).
The second location will be Lalande crater. Lalande crater is in one of the most resource-rich locations on the Moon. The crater has one of the highest concentrations of KREEP (Potassium, Rare Earth Metals, and Phosphorus), the concentration of which is indicated by the abundance of Thorium, which Lalande has at 12 ppm, found at only a few sites on the Moon, with surely higher concentrations in smaller deposits. Thorium is used as fuel for nuclear reactors, which will be used to power the base, as a result of the equatorial location of Lalande, which leaves the base in darkness for two weeks. The proximity to the equator means that a base at Lalande can enter almost all inclinations of an orbit without a high delta-V plane change during the launch. This will considerably reduce the delta-V to reach certain targets, and therefore increase the amount of payload a rocket can carry there. Phosphorus and potassium are two of the three essential nutrients for plants and is used in agricultural fertilizers, which will be required for food, and as a result is required for any self-sufficient space settlement. Lalande is located on the eastern edge of the Mare Insularum, meaning that the area near the crater is not far from both highland and lowland areas of the moon. This allows nearby access to aluminum, considerably more abundant in the highlands than in the lowlands. Iron and Titanium are found in fairly high concentrations in the area, and the young crater has lots of exposed rock of varying composition, perhaps having very pure rocks, making it much easier to refine.
As a third site for resource collection and refining, the Oceanus Procellarum provides the highest concentrations of ilmenite ore, which contains Titanium and Iron. Though not found in the concentrations at Lalande crater, there is some Thorium, and therefore KREEP. As the Oceanus Procellarum is a huge area of the Moon, surveys will have to be done to find the best location for resource prospection.
There is not much to be done with a resource-filled landing site if it cannot be refined and turned into useful products. This is where ISRU comes in.
The commercial basis for the polar settlement will be the production of water ice. In the polar regions of the moon, in the cold depths of a polar crater are the mining robots, equipped with an instrumentation package to detect water ice. Since the water ice are not exposed to sunlight, or be evaporated, temperatures at the bottom of the crater would never rise above 100 kelvin, the robots will require heating elements like an RTG, which can provide marginal power but also massive amounts of heat.
Assuming that the water ice is within a few meters of the surface, the robots should be able to collect the water ice quite easily. The excavating elements must avoid heating the ground, or else the water ice will evaporate and therefore be lost. The collected material will be brought back to the ISRU units, heated above boiling, separating the water ice from the rest of the regolith. As a result of the proximity to the poles, mirrors could eventually be built on the crater rim to heat the material without the use of valuable electricity. Once distilled to separate out other volatiles, the water is cooled into its liquid form. It is then either electrolyzed to create hydrogen and oxygen, or stored in water tanks surrounding the nuclear power source as a radiation shield. The reactor will be Thorium powered, allowing it to be refueled from the KREEP deposits at Lalande.
The ISRU units will be placed some distance away from the deposits, as both the nuclear reactor and the ISRU process will create waste heat that will cook off the deposits before they are ever collected. On Mars, soil with 3% concentration of water can be used to extract 16,788 kilograms in 300 days, with a continuously operating 413 kg extraction system using 2.02 kW of power (NASA, 2009). Our initial ISRU plant will use the SAFE-400 reactor, which produces 100 kW of electricity and amasses 512 kg, without radiators. Assuming we can use the same extraction system with few modifications and scale it up by 45 times, leaving a significant margin for other purposes, a 18,585 kg system can create 755 tons of propellant every year. This is surprisingly high. Ultimately, the design of the propellant plant will be decided by the authority or a contracted company. If relatively pure water ice is found, then production could be much higher. Though the main focus of the polar base will be water, it is not unreasonable for this base to process the rest of the regolith to extract metals and silicon, but that is primarily the focus of the other two bases.
What is the benefit of having this polar base? In addition to having a stable supply of oxygen, water, Now the spacecraft only have to carry the propellant needed to reach the surface of the Moon from their point of origin, without the fuel for the return trip. In addition to the generation of profit, which will encourage the propellant plant to be built in the first place, the polar base serves our long-term goal of space settlement by drastically decreasing the need for Earth-based propellant for transportation in space, and as a result decreasing costs to transport goods like titanium from the Moon by sourcing the propellant from the same location without using propellant to get it there in the first place.
Now we move on Lalande and Oceanus Procellarum, where the focus is on aerospace metals and KREEP. At these colonies, the material is excavated with a cable-operated drag scraper (Gertsch, 1992). On Earth, this design is not very common, as it is requires the machine to be set up when excavating. This process involves anchoring two pulleys and a power unit onto the surface. For mining volatiles, I wanted something that did not require much set up by human workers, but with one base already established, there is less risk in sending workers here. With set-up being infrequent, there is little need to automate the process. The cable is pulled back, and a scraper weighed down by moon rocks gathers the regolith, and dumps it directly into a mill, so there is no need to transport the regolith to a distant mill. The scraper can be changed into a raker, so it can collect rocks instead. The benefits this excavator provides is that it is simple and lightweight, with few moving parts, increasing reliability. A 9 ton version of this could gather as much as 100,000 tons of material every year. The excavators can also be used for buildings launch pads and possibly roads. While later designs should use designs that require no such inconvenient setups, the cable-operated drag scraper provides an effective near-term solution for collecting high amounts of material.
Now that the material has been collected, it must be refined into useful components. To obtain iron and titanium, the Ilmenite is reduced with two hydrogen atoms to produce water, iron, and titanium oxide. In order to separate the titanium oxide, we will use the FFC Cambridge process, which uses molten salt electrolysis to convert titanium oxide into metal (Fenn, Cooley, & Fray, 2004). Titanium and iron can be used as construction material, with water and oxygen serving life support needs. Steel would be preferable to iron, but without a major source of carbon on the Moon, it is unlikely to be created there except at the poles, where some amount of Carbon may exist.
Without significant sources of bauxite, the main ore for aluminum extraction, anorthite (CaAl2Si2O8) is the alternative. Once the rock anorthosite, found commonly in the Lunar Highlands not far from the Lalande site is ground up and the magnetic components separated to leave anorthite. Anorthite can also be reduced using the Cambridge FFC process. The process has to break down all the components of anorthite, increasing the energy cost of the process, but since only one system is needed to process the most valuable of materials, the base is simplified, cutting other operating costs. Additionally, the silicon in anorthite can be used for producing solar panels—even if they are not efficient, the sheer amount of them being produced would eliminate the need to send additional complex nuclear reactors to the base.
The benefits of metal production on the moon are enormous. Equipment can be build very simple, with no mass constraints, allowing the base to fabricate cheap replacements, with the aid of 3D printing, and rapid expansion of the base. Additionally, most of the materials for a space settlement can be sourced from a location much easier to reach. Even the waste material can be used as radiation shielding, for example.
Helium-3 was considered for a major industry in our bases, but basing much of our profit on this rare substance does not reflect near-term reality. Helium-3 is scattered across the entirety of the Moon’s surface, and though the area of Oceanus Procellarum has one of the highest concentrations of helium-3, even here the concentrations of regolith are a miniscule 20 parts per billion. The other materials extracted in the process of extraction would be more valuable overall, making helium-3 at best a side product. More pressingly for a near-future space settlement, there exist no electricity-generating nuclear fusion plants, let alone profitable ones. On top of this, helium-3 fusion is even harder to achieve than the basic fusion. Betting the success of our colony on a resource whose main utility does not even exist yet is extremely risky.
The previous sections discussed the technical aspects of the bases, but what about the way all this and more actually gets built? The authority will cut costs and allow a moon base to be built in the first place, but for building bases that generate the many thousands, even millions of tons of material for the construction of space settlements, something better than shipping everything from Earth is required. What will enable this is the self-replicating factory, which can exponentially expand and easily provide the material for a space colony, with the factory amassing 40,000 tons after just 20 years, starting from a 41 ton seed (Metzger, Muscatello, Mueller, & Mantovani, 2016). The first generation will be brought from Earth, with complex technology, initially teleoperation through humanoid robots and eventually on-site, using resources manufactured on the moon, such as sintered regolith for the cheap construction of pressurized interiors (Indky & Benroya, 2017). The next generation will be crudely made on-site by the first using 3D printers and casts of aluminum or iron, but with each generation the base will get progressively larger and more advanced, becoming more self-autonomous with advances in artificial intelligence, which is on pace to make machines with the same capability as humans in only the next few decades. Later generations will be able to create crude transistors and eventually all the electronic hardware needed for the base, making it completely self-sufficient, with nothing more required from Earth.
Regardless of the specifics, the implications of self-replicating lunar factories is that in a very short time, low cost, and soon, the moon bases can create a major space industry. With solar panel production on scales rivaling that of countries, space solar power becomes commercially competitive as not only launch costs but fabrication costs become practically miniscule. With no limits on territory, these factories are limited only by the resources available on the Moon and eventually in the entire solar system. The authority will make sure that access to the power of this industry is not dominated by a single country and is shared, since even a small lead could result in an effective monopoly as a result of exponential growth. This is the gateway not to the relatively short-term dream of one settlement in space, but to the grand vision of humanity in cities among the stars. And it can start with a few installations on the Moon.
Early transport between the Moon and space will be provided by spacecraft like the ULA XEUS for small to medium-sized cargo, and the BFR upper stage for the largest of payloads. Both of these spacecraft are capable of not only landing but have been suggested for use on the Moon by the respective developers, with the XEUS made specifically to land on the Moon.
However, the Moon bases themselves can construct rockets as their industrial capacity expands. Not only does the Moon have a low gravity a mere 1/6th of Earth, making it far easier to lift off, it also takes 4 times less delta-V to reach orbit, meaning that far less propellant is required, and allows construction to be robust at the expense of mass, especially compared to rockets lifting from Earth. This allows the use of in-situ lunarcrete for the main body of rockets.
The concrete is much like on Earth, using lunar regolith, with cement produced from high calcium lunar rock, and water can be brought from the lunar poles (Ruess, Schaenzlin, Benaroya, 2006). It will be cast in a pressurized environment, and reinforced with Lunar glass, so that less of the material is required. Concrete also has a use in construction, so concrete manufacturing will be a priority in the early base.
The propellant for these rockets can be sourced completely from the Moon. Solid Aluminum and Silicon, both of which are extremely common on the Moon, could produce a respectable Isp of 270 and 272 respectively, as a hybrid rocket with liquid Oxygen as an oxidizer, also in plentiful supply on the Moon (Agosto & Wickman, 1988). Silicon-Oxygen rockets will be used, on account of the fact that silicon can be brought from asteroids, so all the fuel required to and from the Moon does not have to be brought. Early on, such rockets will be the main form of travel between bases, especially between areas where the terrain would be far too difficult to navigate for rovers. Precious hydrogen, better used for interplanetary missions would not be spent on the low delta-V task of lifting from the Moon, and more of it can be delivered to a propellant depot.
Eventually, Rotavators will be built in orbit, putting spacecraft into orbit without the extremely high acceleration for mass drivers, which also require many more complex components, which will have to be brought from Earth early on. The lower gravity of the Moon also means that even extremely long tethers can be built with Zylon, whereas similar LEO tethers would require Carbon Nanotubes. Without aerodynamic drag, the tether can reach down to just above the terrain, so cargo only needs small Aluminum-Oxygen rockets to launch them vertically. Without a powerful magnetic field to boost the orbit of the tether, ion engines will be used. The tether will always evolve, with the tether being reinforced, and anchor mass added from asteroids and the Moon so that the proportion of the mass of the tether and the payloads is far greater, thereby reducing the effect each launch has on the orbit. If timed correctly, the tether can launch payloads directly to EML1 or even directly back to Earth. While a space elevator can be built directly to EML1, rotovators can deliver cargo to a wide variety of targets, and do not require multi-day long rides on cable cars, reducing the life support costs for any manned payloads.
SPACE BASED STUFF (ASTEROIDS?)
There is a debate between the use of resources on the Moon or from asteroids, with no real consensus. However, my conclusion is that asteroids will not be mined first because the Moon is much closer to the Earth than many asteroids, close enough that teleoperation is possible, and allows for a rapid return to Earth in several days rather than weeks in the case of an urgent emergency. Additionally, the Moon is better understood in terms of composition, so there is currently more information for creating an ISRU base, though this will change, and the variety of asteroid compositions results in more varieties of material available. For manufacturing, the Moon allows many of the processes used on Earth, but also does not have access to unique microgravity options either. In the long term, the skyhook concept removes nearly all delta-V needs for access to the Moon, negating the advantage the asteroids possess.
Three main categories of asteroids exist, each with their own special features in regards to prospection. C-type asteroids are made up of up to 20% water, providing an alternative to polar lunar sources. Such asteroids are known to contain organic compounds for agriculture. C-type refers to their carbonaceous composition, making them a source for carbon, which is very rare on the Moon, while it can easily be collected from an asteroid. Carbon is useful for creating a great variety of strong materials like steel, which would allow for the low-cost manufacturing of massive structures like space settlements. This will be the first target for asteroid mining, as an alternative source of propellant to the Moon, once a propellant depot is established at EML1 to fuel the prospectors.
S-type asteroids, specifically that of the LL Chondrite family host high-grade platinum group ores. The price of platinum would drop sharply, but formerly cost-ineffective uses for platinum could become commercially viable, and as a result creating a larger market for the resource. Such asteroids are high in metal, but in this regard, M-type asteroids are even better.
Three options exist for what is actually brought back from the asteroid to cis-Lunar space. The first is to carry the valuable raw material back for refining. The second is to refine the asteroid in-situ, and the third is to redirect the entire asteroid. For large asteroids of over a kilometer in diameter, our main option will be the second one, since there are enough resources there for a long-term operation of multiple years, where it will be worth sending a bulky refinery. If the operation is manned, then habitats will be dug into the asteroid as radiation protection. Smaller asteroids would probably take advantage of the two other options, since they are likely to be mined up in a few missions.
Asteroid mining will complement the operations on the Moon, and will only benefit space settlement, by expanding the materials available for the project.
Atmospheric Oxygen Collector
The issue with the other methods of getting reaction mass for rocket engines is that they all have to come from sources that take several km/s of delta-V to reach, so they are not particularly cost-effective solutions for LEO. A gas scoop within the mass range of the currently flying Falcon 9 FT can collect 757 tons of oxygen each year. The gas scoops cannot provide propellants like hydrogen and methane, but since 6 kilograms of oxygen is burned for every kilogram of hydrogen, it takes away much of the mass. BFR tanker flights would only have to bring the liquid methane, while the ship rendezvous with the scoop for the oxygen. As for the ACES tankers, they would only need to bring the hydrogen from the Moon, so less propellant is consumed to fill up an ACES stage in LEO, saving propellant costs considerably and therefore making a tanker run far more viable. Naturally, the orbit of the gas scoops would decay, but by reducing the cross-section and using electrodynamic tethers, the scoop can maintain orbit for as long as it is needed. By making the biggest contribution to mass in LEO and not having to haul it from the Earth, Moon, or asteroids, gas scoops will allow components that are early on only providable from Earth to be shipped to Moon bases much cheaper and as a result allow the construction of necessary infrastructure to build space settlements available earlier.
Alluded to in previous sections, a transportation hub will be built at the Earth-Moon Lagrange Point One (EML-1) point. The reasoning behind this placement is that EML 4/5 points are stable, but a depot can stay at the EML-1 point for fairly little delta-V. The slight instability of the orbit also means that space debris will not linger around the point. In comparison to L4/5, it takes less delta-V to reach from the Earth or Moon. Additionally, EML-1 can be reached more quickly.
The initial purpose of the station here will be as a propellant depot, in order to cut the amount of propellant and cost required to travel to the Moon, accelerating the rate at which infrastructure is constructed. A major customer may be missions destined for Mars and other interplanetary destinations, which no longer have to carry their propellant into space, and can instead receive them from the Moon. From EML-1, it only takes a mere 1.2 km/s for a trajectory to Mars, where aerobraking can be used to slow a ship down without the use of propellant. Services like this will be one of the early sources of income for the authority which will allow it to become more independent from governments, making it even more stable and allowing more natural growth to take place.