A Cislunar Civilization:
Townships in Space
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When we talk of expanding Humanity’s realm into space and building an extraterrestrial civilization, we generally imagine fantastic domed cities on the surface of the moon and on the surfaces of other planets (especially Mars) and their moons with some mining colonies on certain of the asteroids. If we think of free-flying objects, we think of them as ships or space stations and we don’t conceive those as being big enough to contain cities. But in the mid-1970's Professor Gerard K. O’Neill and his engineering students at Princeton University discovered that the surface of the moon or of a planet is not the best place to build an electro-mechanical civilization, the more so if people can draw on the resources contained in comets and asteroids.
Professor O’Neill had given his students the challenge of devising the best way to build and operate an array of large solar-power satellites, using the technology of the recently ended Apollo space program. In the O’Neill plan people began by building a colony on the moon, where they used solar power to render the regolith into construction materials. Using an electromagnetic catapult, the lunar colonists heaved blocks of material onto trajectories that passed through Lagrange-2, high above the far side of the moon, where an automated device caught them in a net and gathered them in a container. When the container was full, an automated rocket barged it to Lagrange-5, a region sixty degrees behind the moon on the moon’s orbit. There workers and their machines used the material, along with some materials brought from Earth, to build a small space colony, either in the form of a cylinder or a torus. When the colony was finished and populated, the people used lunar material to make solar-power satellites, which automated rockets barged into geosynchronous orbit. Once in their proper orbits, the solar-power satellites converted sunlight into microwaves, which were beamed to receivers on Earth to be converted into and used as electricity.
With Apollo-level technology the O’Neill plan was barely feasible. With the technology of the Space Shuttle it’s even more feasible. Enacting it would be a good first step toward building an interplanetary civilization and we would well expect our spacefaring technology to improve in the course of taking that first step. It requires a large investment of people’s time and effort spread widely across a large number of industries, but it repays that investment in the cheap, non-polluting electricity that it produces.
As a first step toward building a civilization in space, the O’Neill plan is perfect. It is a tremendous challenge, certainly, but the nation that wants to see its culture dominate the solar system will accept that challenge. Once they have met that challenge, the people of that nation must ask What is the second step?
Usually we think of expeditions to Mars and the establishment of colonies on that planet as the natural follow-on to the establishment of colonies on the moon. Those events will almost certainly happen, but not for a long time. We still don’t know how astronauts can cope with the high-energy radiation that permeates interplanetary space, so some time will pass before anyone sends people on eight-month voyages to Mars. Meanwhile, we can and should be doing other things.
For the second step of moving Humanity into space, the best choice builds on the O’Neill plan and builds free-floating townships in space. At the beginning of this stage the space colony at Lagrange-5 will have demonstrated how a small town can become more-or-less self-sufficient in space. Drawing progressively fewer resources from the moon and from Earth, the colonists at this stage have developed zero-gee farming using a modified hydroponic system that mimics the ancient Aztec chinampa system of farming. The colonists’ diet will likely be vegetarian with some fish and eggs. The colonists will be living in an almost complete closed-cycle system, a system that they will continue improving.
When the demand for new solar-power satellites diminishes, the space colony will begin building large, robotic interplanetary ships. Using the most efficient engines available, those ships will go to the Asteroid Belt or visit comets and extract resources, primarily light elements, from them for return to the Earth-moon system. As those ships pursue their missions, problems will appear and people will solve them, adding improvements to the ships over time and thereby making the project ever more efficient.
At the same time humans and robots will build a second town on the moon. This one will lie in the center of the far side, so that material catapulted into space will go directly onto trajectories that graze lower orbits around Earth. The town’s residents, human and mechanical, will process the regolith into construction materials and their chief byproduct, oxygen. Rocketships will land with an excess of liquid methane and take on extra liquid oxygen along with a cargo of construction materials bound for Earth orbit.
Rocketships meant to land on and take off from the moon will use chemical-burning engines at first, most likely using liquid methane and liquid oxygen as propellants. Those engines produce the kind of thrust that a spaceship needs for landing on bodies with a substantially stiff gravitational field. In free space, where they can use low thrust, the rocketships will use ion engines or plasma rockets for their superior specific impulse.
Although at first rockets must land on the moon vertically and take off the same way, doing those things horizontally is more efficient. In the vertical case, part of the rocket’s thrust must support the weight of the ship as the rest of the thrust accelerates or decelerates it. In the horizontal case, some other means, such as a magnetic levitation track, counters lunar gravity as the ship shifts between a standstill and orbital speed, thereby saving the ship propellant.
In order to go from a standstill to circumlunar orbital speed, a rocketship must change its speed by 1.6783 kilometers per second. If it does so at ten gees (98.1 meters per second per second), it will take 17.1 seconds to make that change in speed and will cross 14.343 kilometers of distance. Humans might have some difficulty with ten gees, but robots won’t mind at all and most of our rocketships will be robots. Thus a 29-kilometer catapult (one half for decelerating incoming ships and half for accelerating outgoing ships) will be built next to each of our lunar cities.
Cities don’t appear in random locations: there are sound reasons why they appear where they do, reasons why people settle in that place and not another. Inevitably the location provides some resource that people need in their chosen work. Once people move in to take advantage of such resources, other people will move in to provide other goods and services that people need.
Consider: a short, fast-flowing river connects two lakes that lie at different altitudes above sea level. For most of history people paid little attention to the site. But when manufacturers began harnessing the river to drive their machinery, a city grew up around it, the City of Tampere in Finland.
Many great cities have grown up around ports, places where ships can safely ride at anchor or tie up to docks to onload or offload cargo and passengers (think of New York City). Transportation networks radiate away from these cities and draw in people and goods. But ports don’t exist only on seacoasts. The City of Moskva (Moscow) in Russia stands on what was once a portage between two systems of navigable rivers that connected Scandinavia to the Byzantine Empire.
Sometimes a city’s initial reason for existing is obscured by later developments. The gambling Mecca of Las Vegas (The Meadows in Spanish), Nevada, lies in a desert far from major population centers, which seems a strange location. Initially the town lay on the outwash of a system of gullies. The dirt and sand washed down from the surrounding mountains retains enough water to support the growth of grass in meadows (hence the city’s name) where sheep grazed. When a railroad was built through the area, workers drilled a well to acquire water for the steam locomotives of the time: the city started out as a small tank town. In the late 1940's several mobsters, fleeing the East Coast and looking to acquire easy money, took advantage of Nevada’s gambling laws and established a casino and hotel in the town. Now a town that once served a now obsolete technology glows in the night as an entertainment venue.
Where in space will people build their cities? What resources depend upon location? This early in the Space Age the most valuable resources are trajectories and orbits. We see one good example in the geosynchronous orbit, nearly a quarter of a million kilometers of prime real estate in Earth’s equatorial plane, ideal for communications satellites and solar-power satellites, which need to keep their antennae pointed at locations on Earth’s surface.
Another good place for a city lies near the geographical center of the far side of the moon. From that place an object catapulted horizontally with sufficient speed (at least 2.3735 kilometers per second) will follow a trajectory that will graze a low-Earth orbit or even Earth’s atmosphere (as the Apollo spacecraft did). If cargoes are launched on their own rockets, those rockets can insert them into their destination orbits. In that way lunar-derived material can be sent to construction sites around Earth.
As for the free-floating cities, we could put them anywhere. The first ones should go into orbits less than 65,000 kilometers from Earth’s center. That puts them inside Earth’s magnetosphere, which will provide protection from cosmic radiation. Once scientists and engineers devise ways to cope with the more intense radiation of deep space, cities can be built further out.
It takes more rocketpower to put a ship approaching Earth from interplanetary space into a low orbit than into a higher orbit. Thus, the highest feasible orbit, one in which an object takes a little less than two days to revolve once around Earth, gives us a good place to build our first interplanetary spaceport. Thence robotic ships will head out into deep space and thither they will return from the outer solar system with their cargoes of materials harvested from asteroids and comets.
Imagine visiting that port and watching a giant freighter, its ion engines glowing, glide gracefully into a dock as it matches speed with the city. Robots will offload the cargo and send it to rendering plants and factories that will transform it into propellant, building material, and other goods that can be transshipped to cities in lower orbits or to the moon. As with most ports, this one will grow. Additional habitat modules and farms will be built and other ports will be built on the same orbit.
One free-floating township will lie on an orbit just outside the geosynchronous orbit, perhaps only a few hundred kilometers above it. The inhabitants of that city will take as their responsibility the maintenance and repair of the solar-power satellites, which will drift past the town on their lower orbit. As the number of solar-power satellites grows, so will the town. Like the high port, it may also produce clones on the same orbit, with each of the towns being responsible for a certain subset of the power satellites.
Another town will float on a low-Earth orbit. This town will also be a port, to which rockets from Earth will bring cargoes and passengers. It must float as close to Earth as possible and yet rise high enough that the atmosphere will be thin enough that it won’t cause significant drag on the town: that criterion puts the town at least 300 kilometers above mean sea level. Even so, the town will be elongated and, at least partly, streamlined. Structures on the town may also function as ion engines, using the ionized wisps of upper atmosphere as propellant. Those engines’ thrust will maintain the town’s speed on its orbit.
On the geosynchronous orbit, communications satellites and weather satellites will be absorbed into towns that will grow into major communications centers.
How to build a township in space.
We start with a Stanford Torus. It looks like a wheel with a diameter of 1.79 kilometers and a minor diameter of 130 meters, which gives its living space a raw floor area of 734,760 square meters. To create the effect of normal gravity inside its living space, the wheel revolves at the rate of one revolution per minute. This little town will support several thousand people. Now we want to see how people will build one.
1. Robotic rockets put cargoes of components and building materials, coming from both Earth and the moon, into orbit where the town will float. The first towns will float on orbits with radii less than 65,000 kilometers (with periods of less than 1.914 days), which puts them within Earth’s magnetosphere. We want to put our first one in the widest of those orbits, where it will serve as an interplanetary port.
2. Using materials and components brought from Earth, teams of people and robots will build a construction shack in low Earth orbit. The shack will contain tools and living quarters for the crews building the town. As the completed shack is barged into a higher orbit the first construction crew, human and mechanical, will ride with it. At the construction site the shack will dock with the supplies already there, which supplies have docked with each other as they arrived.
3.The crew, guiding the robots, establishes the solar-power array some distance from the construction shack and connected to it through cables. If the solar-power array floats above or below the construction shack, orbital tidal forces will pull it gently away from the shack and draw the cables taut. To keep the shack properly on orbit, the crew will deploy two identical solar-power arrays in opposite directions. Thus the crew will gain enough electricity to build the town.
4. Using the construction shack as an anchor point, the team will begin building the axle of the town. They will use the construction materials that have already arrived to build the axle’s skeleton and begin building the first hydroponic farms, which will be connected to the axle through pressurized tubes. Each farm will consist of a long tube with a crescent-shaped cross section. The inner arc of the crescent will consist of thick blocks of toughened borosilicate glass, so that when the farm is pressurized the blocks will be held in compression. The glass will allow sunlight to enter the farm, but will block high-energy radiation. An outer layer of glass or plastic will serve as an anti-meteoroid shield. Cables supporting that shield will also, through their tension, prevent the outer arc of the crescent from flexing outward when the farm is pressurized.
5. The crew will fill the growing axle with machine shops, robot maintenance facilities, and expanded living quarters for humans. As those extra quarters are completed, more crews will arrive to increase the pace of construction.
With extra personnel, the crews will build a second section of the axle, one that rotates at one revolution per minute. The two axles will be separated from one another by a gap perhaps twenty meters wide. An airtight container, almost as long as the gap is wide, floats docked to one of the axles. A metal frame jutting from the non-rotating axle will hold linear-induction motors that will move the container from one axle to the other while also rotating it to match the rotation of the axle to which it is moved. The container will be used to move materials and people between the axles and it actually provides a more efficient system than airlocks or airtight rotating collars. We would also see, surrounding the frame holding the container, a ring of microwave antennae on the non-rotating axle and a ring of rectifying antennae on the rotating axle. Electricity produced by the solar-power arrays will be converted into microwaves and transmitted across the gap and converted back into electricity.
6. Robots will braid aluminum wire or carbon-fiber cords into rope and cut the rope to precisely determined lengths. They will then build the foundation of the town somewhat in the manner of constructing a suspension bridge. Robots will weld the ends of the ropes together to create loops and then they will attach each loop to a rotating frame centered on the axle. The frame, itself a robot, will use ion engines to spin up, using centrifugal force to shape the loop into a circle. The frame will place the first loop in space and then place subsequent loops where robots will weld them to it and to each other, building up the tire-shaped foundation of the town. Two rotating frames will enable the robots to build the foundation symmetrically.
7. When the robots have finished building the opaque part of the wheel, the crews will build a set of spokes to connect it to the axle. Springs, shock absorbers, and expansion joints will come between the spokes and the axle in order to damp out any small radial motions that may come between the wheel and the axle. Doubling as skyscraper office buildings, the spokes will contain elevators and other conveyances (such as piping for air and water). Again, the frames will serve as construction cranes, lowering components into place and spinning them up to match the rotation of the wheel. To prevent vibration, parts of equal masses will be lowered on opposite sides of the axle.
8. Brackets connected to each other by cable arrays will be lowered by the frames working in tandem and attached to the rims of the wheel. When the cables are properly tensioned, the brackets will support the glass arches that form the ceiling of the habitat space: they will prevent the rims from spreading apart under the pressure of the glass arches. The cables will be made of a material with minimal thermal expansion, so they won’t change their lengths significantly during the day/night cycle. Water circulating through pipes mounted on the cables can also moderate the temperature of the cables and thereby mitigate expansion and contraction. Those pipes will also supply sprinklers to provide rain in the town as an air freshener.
9. Erecting arches made of glass blocks offers a bit of a challenge. The arches have to span 130 meters and be thick enough that their weight, due to the centrifugal force of the wheel’s rotation, will hold down the wheel’s atmosphere. Our primary question here asks How do the builders support the arches while they’re being assembled? For each meter of the ceiling’s length the arches ponder over 1325 tonnes: the whole ceiling ponders 7,486, 250 tonnes. We want the glass to be over three meters thick so that the ceiling will also serve as a radiation shield.
A large aluminum form will span the wheel and hold the first course of glass blocks, the underside of the arch. As the blocks come down, the robots will put silicone rubber on the edges so that the joints will be suitably flexible and airtight. Additional courses of blocks will be laid on the arch and then the form will be lowered and moved to support construction of the next section of the arch.
As each block is lowered from the axle to the wheel, its speed must increase from zero to 94.2 meters per second (212 miles per hour). Again, the rotating frames will supply the necessary acceleration. Two teams on opposite sides of the wheel (necessary to keep the wheel balanced), each laying five meters per day, will take 565 days to build the ceiling.
10. As the arch construction moves around the wheel, other crews will lay an air-tight shield on the floor and walls of the wheel. That shield will have to be thick, flexible, and resistant to corrosion; that is, it must be tough enough to endure having a small town living on it. They will build a frame on that shield and on it build the ground level of the town. Built like an amusement park, the town will have tunnels and storage chambers "underground".
11. Once the crews have completed the air-tightening, they will put the atmosphere into the town. If they choose to use a normal atmosphere, then in the wheel itself they will need to insert 216,000 tonnes of nitrogen and 58,170 tonnes of oxygen. Presumably coming from Earth, the nitrogen will cost, at $2000 per kilogram (a reasonable Earth to high orbit cost), 432 billion dollars: the oxygen, coming from the moon, will cost a great deal less. Additional quantities of atmospheric gases will also be needed for the spokes, the axle, and the farms. Water will also have to be brought in to complete the conversion of this shell into a giant version of the microcosms that we used to make in our high-school biology classes. As air fills the structure, robots will conduct leak tests and patch over any leaks that they find.
12. Large tanks in the wheel’s "underground" part will contain water, meant for the sprinklers and the inhabitants’ needs (drinking, bathing, etc.). Automated machinery will move the water and use its mass to keep the wheel balanced as people, robots, and their possessions move about. With the atmosphere established inside the structure, people and robots will begin building their town.
People and robots will construct the buildings from light and strong materials such as metal or ceramic foam or natural materials such as bamboo (perhaps tweaked a bit through genetic engineering). If our town is to contain 10,000 inhabitants, each will need 73.5 square meters of the floor space (8.6 meters squared), the size of a small apartment. To leave room for a walkway, a bicycle path, and gardens (decorative plants will freshen and perfume the air in addition to providing aesthetic value), the builders will raise the housing two or three stories. Any offices or shops that the town needs will go into and immediately around the spokes, which will rise over the town like skyscrapers.
13. The foundation of the wheel may not be thick enough to attenuate high-energy radiation fully. That’s one reason for putting the first towns inside Earth’s magnetosphere. To provide extra shielding, the builders can construct a thick ceramic "tire" that fits around the wheel without touching it. The wheel and the shield will be equipped with magnetic runners and magnetic tracks, which will enable the robots controlling the town to keep the two objects from touching each other.
Even with the use of robotic labor, building these townships and cities will take a tremendous amount of human effort and can only be justified by tremendous human benefit, both of which we represent through the flow of money. Building a civilization in space is as much a financial challenge as it is a scientific and engineering one. Gerard O’Neill and his students found that, although it necessitated a large initial investment of money, their plan would pay for itself in a reasonable elapse of time through the sale of the electricity that the power satellites beamed to Earth. In an extension of that plan, the ports will pay for themselves through docking fees, as ports have always done. The use of robotic labor will help reduce the initial investment. The lunar towns will produce liquid oxygen and construction materials and the sales of those goods will support the towns and their growth.
Who will make such an investment as this project requires? Who has the means, both technological and financial, as well as the vision and the will to do it?
The United States of America had an opportunity in the late 1970's to begin enacting the O’Neill plan. The rockets could have been developed as part of the then-beginning Space Shuttle program and the project could have offered a wonderful alternative to the overbloating of the military-industrial complex, against which President Eisenhower warned us. But we lacked the will to take on such a grand challenge, one prominent politician even ridiculing the idea as "a nutty fantasy". We still lack the will: we’ve even shut down the Space Shuttle program, which was a half-hearted affair that never achieved its full potential, and we have nothing to replace it. We lack vision above all: we no longer conceive Americans as a spacefaring people.
The Russians don’t have the means and also appear to lack vision. To launch people and payloads into low-Earth orbit, they are still using a rocket, the Proton, that they developed in the late 1960's. Their heavy-lift rocket, the Energia, flew only a few times in the 1990's and hasn’t been used since. The collapse of the Soviet Union left Russia more or less destitute and the country came to be dominated by criminals. The struggle against that degradation will continue for some time.
Only one other nation has, as of this writing (Aug 2017), used its own rockets to send people into space and their first people carrier was a three-seater, similar to America’s Apollo spacecraft. In addition, the Chinese have already announced their intent to send taikonauts to the moon in the near future. China has the financial means available and is developing the technological means to enact the O’Neill plan. The Chinese also have incentive to develop a cislunar civilization, the desire for a source of abundant and non-polluting electric power. If the Chinese develop the vision and the will, then by the end of this century the solar system will be a province of China.
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