During the final stages of construction of the habitat, colonists begin immigrating to L5. Within a few years a small but thriving human community is established. Its architecture, agriculture, commerce, culture, and even the individual people reflect a dedicated emphasis on productivity.
Imagine that you are a visitor on a tour of this colony. Your experiences during such a visit are shown in italics in this chapter to act as counterpoints to the continuing technical descriptions which conform with the arrangement of the other material in this report.
Preparation for your trip is a difficult period; it eliminates those who are not serious about their intention of going to the space colony. You undergo weeks of quarantine, exhaustive physical examinations, stringent decontamination, and interminable tests to make sure that you do not carry insects, bacteria, fungi, or mental problems to L5. Only then are you permitted to board a personnel module of a heavy-lift launch vehicle which everyone refers to as the HLLV, along with 99 prospective colonists who have gone through even more rigorous tests than you have as a mere visitor.
In the following hour events move at breakneck speed. Your vehicle is launched. Acceleration thrusts you into your contoured seat. Minutes later it ceases and you are in orbit 240 km above the Earth and having your first experience of being weightless. The orbit is a staging area at which an entire section of the HLLV, the personnel carrier containing you and the colonists, is transferred to an inter-orbital transport vehicle known as the IOTV. This is the workhorse transporter that moves people and cargoes between points in space, and never lands upon any planetary body. Its structure seems frail and delicate compared with the airplane-like structure of the HLLV.
During the construction phase of the colony, the staging area handled replacement supplies at the rate of 1000 t a year. The growth and increasing population loading of the colony required transshipment of an average of 50 people per week together with their personal belongings and the additional carbon, nitrogen, and hydrogen needed to sustain them in space. Oxygen, and other elements, are obtained from the Moon. Later the big demand was for lightweight, complex components fabricated for satellite solar power stations. Initially the supply of the lunar base also came from Earth. The 150 people on the Moon require 250 t of supplies and rotation of 75 people to Earth each year. Furthermore, there is traffic from the colony to Earth. Studies of past colonizations on Earth have shown that discontent with frontier life is usually such that many colonists wish to return home.
Cargo was brought up on earlier flights of HLLV's so that you do not have to wait long in the staging orbit. This reduces the amount of consumables needed to support the people between Earth and the colony. Every effort is made to get you to the colony as quickly as possible once you have attained Earth orbit. The freight had been transferred to the IOTV before your arrival, so no time is lost in moving the personnel carrier from the HLLV to the IOTV. The rocket engines of the IOTV begin to thrust and the vehicle breaks from Earth orbit and begins its 5-day journey to L5. You find that conditions within the personnel carrier are crowded, somewhat like the transcontinental charter flights you experienced on Earth.
Like countless other tourists over the years you look for the first view of your destination. Just as European immigrants looked for the concrete towers of New York and the torch-bearing statue, you now anxiously await your first glimpse of the wheel-like structure spinning amid the black backdrop of space. Only in the last day before your arrival is your search rewarded And then you are surprised at how small the space colony looks Since you cannot judge distance in space, the colony appears first as a mere point of light that gradually exceeds the other stars in brightness, and then it forms into a narrow band of sunlight reflected from the radiation shield. Later you see the spokes and the hub. But still the 10 million tonnes of slag and Moon dust that have been compacted and placed around the habitat like a bicycle tire, seem no larger than the rim of a balance wheel in a ladies' watch.
Only in the last few hours of the trip, when the IOTV has matched its orbit with that of the colony and is waiting to dock, do you see the true extent of the habitat and begin to comprehend the immense nature of this man-made structure in space.
The View From the Outside
The space colony appears as a giant wheel in space. Still you cannot comprehend its size, but you know it must be huge. One of the other passengers who has been on the trip before tells you it is 1800 m in diameter. He points to the six spokes connecting the wheel rim to its hub and tells you each is five times as wide across as is the cabin of your space transport. You look in awe. He tells you that the rough-looking outer "tire"is really a radiation shield built of rubble from the Moon. It protects the colony's inhabitants from cosmic rays.
In reply to your question about the burnished disc that hangs suspended above the wheel of the space colony, he explains that it is a big mirror reflecting sunlight to other mirrors which, in turn, direct the light rays through several other mirrors arranged in a chevron form to block cosmic rays.
As you watch you become aware that the spokes are rotating, but you cannot see any motion in the rim. Again your companion explains; the habitat rotates within the outer shield. Rotation is needed to simulate gravity, but rotating the massive shield would produce high stresses that would require a much stronger structure. The inner habitat tube is accurately positioned within the outer shield so that the two do not scrape against each other.
He points to the hub of the wheel and tells you that is where your transport is heading to dock with the space colony, explaining that local custom has named the docking area the North Pole.
Figure 5-l presents a general perspective of the principal components of the habitat. The torus provides the space for housing, agriculture, community activities, and light industry within a 130-m-diam tube bent into a wheel approximately 1800m in diameter. Six spokes, each 15 m in diameter, connect the torus to a central hub and accommodate elevators, power cables, and heat exchange pipes between the torus and the hub. The spokes also act as diametric crossties to resist excessive deformations of the torus from internal concentrations of masses on opposite parts of the wheel. Glass windows mounted on aluminum ribs cover 1/3 of the surface of the torus and admit sunlight "downward" onto the agricultural and residential areas. The remaining 2/3 of the shell of the torus is constructed of aluminum plates. Details are given in appendix A.
Passive shielding against cosmic rays is a separate, unconnected shell with a gap of approximately 1-1/2 m between it and the torus. The shield, 1.7 m thick, is constructed from large "bricks" of fused undifferentiated lunar soil held together by mechanical fasteners. Over the window region the shield is shaped in the form of "chevrons" with mirrored surfaces which pass light by a succession of reflections but block cosmic rays. The shield and chevron configuration is illustrated in figure 5-2. (For a more detailed explanation see appendices E and K.)
If the shield is used as a reaction mass during spin-up of the torus it would counter-rotate at approximately 0.07 rpm; the relative velocity between the shield and the torus, would thus be about 100 m/s. The torus is prevented from scraping against the shield by a positive positioning device.
The stationary main mirror located above the docking area of the space colony reflects sunlight parallel to the axis of rotation onto the rotating ring of secondary mirrors which illuminate the windows (see figs. 5-1 and 5-2). The secondary mirrors are segmented and each segment is individually directed to regulate the amount of light entering the habitat. The flux of light in space is 1400W/m^2, but requirements in the torus vary from 200 W/m^2 in the residential areas to 1000 W/m^2 in the agricultural areas. Furthermore, a diurnal cycle is required in residential and some agricultural areas, while other agricultural regions require continuous solar radiation. This is achieved by directing the light away from certain windows to obtain darkness and by concentrating the light from several mirrors onto other windows to meet the high flux demands.
As your ship moves smoothly toward the docking area, you become aware of the details of this gigantic wheel-like structure. You see the 100-m-diam fabrication sphere on the "south" side of the central hub. Your companion tells you this is where metals are shaped and formed and where much of the assembly and construction takes place. To one side of the fabrication sphere is a 200 MW solar power plant and furnace used in fabrication; in the opposite direction you see the dimly visible 4.9 X 105 m^2 expanse of the habitat's radiator with its edge toward the Sun. It radiates into space the waste heat of the habitat delivered to it by a complex of heat exchangers passing through the spokes from the torus to the hub. Like the docking area at the North Pole, the fabrication sphere and radiator do not rotate. (See fig. 5-3.)
As the IOTV passes over the spokes toward the hub you see areas of silicon solar cells suspended between the spokes, central hub, and secondary mirrors. Because they look northward toward the main mirror, these cells are sheltered by the other mirrors from the degrading effects of the solar wind. Your fellow passenger tells you they supply 50 MW of electric power required by the habitat. If control of the main mirror were accidently lost or some other accident should cause loss of solar power, the 200 MW solar power station at the extraction facility, would supply emergency power.
The IOTV moves almost imperceptibly through the last few meters and gently attaches itself to one of the docking ports. All people and equipment for the habitat pass through these ports. There is an unexpected lack of officials and there are no landing formalities. One agent oversees unloading; a second acts as a guide to the passengers. Labor is scarce so that the colony cannot support a bureaucracy, explains your companion.
Passing from the docking module, you see the walls of the central hub moving slowly by you as you float freely under zero-g. You are now in the rotating habitat, but because you are near the axix of rotation, the rotation rate of 1 rpm gives no appreciable sensation of weight. In fact, a few workers on their lunch break can be seen cavorting in the almost zero-g of the central hub playing an unusual type of ballgame, invented by earlier construction workers.
The hub is, howver, much more than a playground, it is a crucial crossroads for the whole colony. Six spokes converge from the torus to this 130-m-diam sphere and emerge from its walls. They carry the power cables and heat exchangers that connect the interior of the habitat to the external power supplies and the radiator. They also serve as elevator shafts through which several thousand commuters travel each day to and from their work in the fabrication sphere or outside the habitat. Now with the other new arrivals you enter an elevator in one of these spokes and begin the 830-m trip out to the torus. As the elevator moves and the sense of "gravity" begins, you realize that "out" is really "down."
A Residential Area
Emerging from the elevator your fellow passengers go their varous ways as you enter a busy community without skyscrapers and freeways; a city which does not dwarf its inhabitants. The human scale of the architecture is emphsized by the long lines of sight, the frequent clusters of small fruit trees and parks, and the sense of openness produced by the broad expanse of yellow sunlight streaming down from far overhead. This is the central plain running the full circumference of the torus along the middle of the tube.
Houses are the most numerous structures. You are impressed by the architectural achievement in housing 10,000 people on 43 ha {106 acres) while maintaining a spacious environment. Spaciousness is achieved by terracing structures up the curved walls of the torus and also by placing much of the commerce (e.g., large shops, light industry, mechanical subsystems) in the volume of the torus which lies below the central plain on which most inhabitants live. Houses have plenty of window area to provide a sense of openness. Walls and doors are only needed for acoustical and visual privacy and not for protection from the weather.
Housing in the space colony (see fig. 5-4) is modular, permitting a variety of spaces and forms - clusters of one- or two-level homes, groups of structures as high as four and five stories, and terraced homes along the edges of the plain. Use of the modular components is illustrated in figures 5-5 to 5-7. (For more information see appendix B.) As noted in chapters 2 and 3 the total projected area (defined in appendix B of ch. 3) required in the torus is 43 m^2/person for residential and community life, 4 m^2 /person for mechanical and life support subsystems, and 20m^2/person for agriculture and food processing. Figure 5-8 (overleaf) illustrates these projected areas in terms of total surface area and the number of levels required for each function. By making use of multiple layers above and below the central plain, the apparent population density in the colony is reduced. Layers below the central plain are illuminated artificially. Figure 5-9, a longitudinal section of the toroid's tube, illustrates schematically the layers of the colony below the central plain. All the architecture within the enclosure of the torus must be distributed to satisfy several requirements:
TABLE 5-1 (gif format)
| Description | Surface area, m^2 | Projected area, m^2 |
Volume, m^3 |
|---|---|---|---|
| Community Area | 980,000 | 430,000 | 8 X 10^6 |
| Agriculture, processing and mechanical | 650,000 | 240,000 | 10 X 10^6 |
| Total required | 1,680,000 | 670,000 | 18 X 10^6 |
| Total available | 678,000 | 69 X 10^6 |
You are aware that the colony has filled up over the preceeding 4 yr at the rate of about 2000 people per year. Consequently, the houses close to the elevator are already occupied. Since you are a latecomer and also only a temporary visitor, your apartment is some 400 m from where you enter into the torus. This is about the greatest distance anyone resides from an elevator, and the walk takes only 5 min. You might buy a bicycle if you were staying longer. Alternatively you can choose to walk 60 m to the ring road which passes around the torus at the edge of the plain and catch a transport car to the stop nearest your destination. Since you are a tourist and want to see what is going on, you decide to walk and start off down a tree-lined pedestrian way following the directions on the map you were given when you landed.
Equally as striking as the lack of traffic and wide roads is the presence of a flourishing vegetation. Stimulated by plentiful sunshine, brilliantly colored flowers bloom in profusion along winding walkways. You meet a colonist heading in the same direction as yourself. She tells you she is an engineer at the habitat controls center and is one of those responsible for the maintenance, modification, and control of the mechanical and electrical systems. A few questions about this gigantic and complex structure bring forth a flood of information from your companion. To resist the atmospheric pressure and the centrifugal forces of its own mass as well as the internal masses, the shell has a skin thickness of 2.1 cm. The windows through which sunlight streams are some 65 m "above" you and are 2.8 cm thick. Buried in the walls and under the decks of the torus are thousands of kilometers of wires and piping for electrical power distribution, water supply, waste disposal, and air dehumidifying.
The shell of the torus is designed to resist loads of 50 kPa of atmospheric pressure and the centrifugal forces of its own mass as well as 530,000 t of internal mass. Including the ribbed portion, the mass of the aluminum shell is 156,000 t. (Details of the design are presented in appendix A.) For the windows to resist the pressure of the atmosphere across a span of 0.5 m, the distance between ribs, the glass is 2.8 cm thick. This requires 48,000 t of glass. The masses of the main components of the habitat (except for the extraction plant) are listed in table 5-2; the principal internal masses are summarized in table 5-3.
TABLE 5-2 (gif format)
| Mass, t | |||
|---|---|---|---|
| Item | From lunar ore | From Earth | |
| Shield | 9,900,000 | --- | |
| Torus shell | 156,000 | --- | |
| Glass solars | 48,000 | --- | |
| Spokes | 2,400 | --- | |
| Central hub | 1,600 | --- | |
| Docking module | 100 | --- | |
| Fabrication sphere | --- | 500 | |
| Radiators | 2,400 | --- | |
| Habitat power station | 700 | --- | |
| Main mirror | 200 | 7 (Mylar) | |
| Secondary mirrors | 90 | 3 (Mylar) | |
TABLE 5-3 (gif format)
| Item | Mass, t |
|---|---|
| Soil (dry) - 1,000,000 m^2, 0.3 m thick 721 kg/m^3 |
220,000 |
| Water in soil (10% soil) | 22,000 |
| Water, other | 20,000 |
| Biomass - people | 600 |
| Biomass - animals | 900 |
| Biomass - plants | 5,000 |
| Structures | 77,000 |
| Substructures (20% of structures) | 15,000 |
| Furniture, appliances | 20,000 |
| Machinery | 40,000 |
| Utilities | 29,500 |
| Miscellaneous (extra) | 80,000 |
| Total | 530,000 |
Arriving at your apartment house you bid the other colonist goodbye. The house is a combination of two duplexes and two studio apartments (see appendix B). Each of the studio apartments on the third floor has a small balcony on which some plants are growing. On a neighbor's balcony is an impressive stand of cherry tomatoes and lettuce in a few pots Small patios below each balcony are surrounded by dwarf apple and peach trees. Although small (49 m^2) your apartment is completely furnished in a compact, convenient and attractive way. Furniture and the few ornaments are made of aluminum and ceramics, a constant reminder that wood and plastics must come from Earth, or be made from carbon, nitrogen and hydrogen brought from Earth It takes a while to become accustomed to the almost complete absence of wood and plastics.
Although the apartment has a kitchenette, you decide it will be more convenient and pleasant to eat in one of the neighborhood community kitchens where you can meet and get to know neighbors as you dine with them. So you walk to the closest of these kitchens.
A glance around the dining area reveals young adults and a few children. Briefings before you left Earth had informed you that the community of the space habitat consists of men and women between the ages of 18 and 40, a few hundred children who came with their parents from Earth, and about a hundred children who were born in the colony. The popupation mix is that of a typical terrestrial frontier - it is hardworking, concentrating intently on the manufacture of satellite solar power stations and the construction of the next colony, a replica of this one.
As you sit down to eat, one of the few colony elders tells you of the philosophy behind the productivity and growth in the colony.
Despite the narrow focus of activities in the colony, he explains, there is considerable stimulation and innovation by the new settlers The rapid growth of the settlement sustains a sense of dynamic change; but he warns that the stabilization of the community upon reaching its full size may result in the dissipation of that sense (ref. 1). A community as small and as isolated as the colony may stagnate and decline in productivity and attractiveness The answer to the problem is continued growth by the addition of more colonies. Growth is important economically as wed as psychologically, because as time passes the population will become more like that of Earth in its age distribution, with the productive fraction of the population diminishing from about 70 percent to between 30 percent and 40 percent. If more colonies are not established, the amount of production will decrease with time. He points out that only if the total number of people grows rapidly can production in space be maintained at its initial level and be increased sufficiently to meet growing demands of Earth's markets for satellite solar power stations Furthermore, he explains, the aggregation of habitats into larger communities will enable the colonies to develop cultural and technological diversity similar to that which permits the larger cities of Earth to be centers of innovation and disseminators of cultural and technological change.
The colony experiences the egalitarianism of a frontier reinforced by the esprit of a group of people working together with a sense of mission on a common task. His face glowed with enthusiasm as he declared that this spirit, more than heroic adventures or romanticized challenge, is what makes the colony a rewarding place to live. Egalitarianism is tempered by certain realities within the colony. The entire colony has a sense of elitism simply because each individual colonist was selected as a settler. A distinction developing between those with clean and "shirtsleeve" jobs and those who work in hazardous, heavy industry, or zero atmosphere jobs, has only small effects and will not produce marked socio-economic differentiation for a number of years.
He excuses himself, saying he has a meeting of the "elders" to attend.
You continue eating alone. Your meal is satisfying- chicken, peas, and rice followed by apple pie for dessert - hardly the fare which science fiction writers led you to expect. There are no dehydrated "miracle" foods or algae cake because the colony is equipped with extraordinarily productive farms that raise food familiar to people on Earth Your interest is aroused and you decide to tour the agricultural area next to see how this food variety is achieved.
An Agricultural Area
To promote diversity and to build in redundancy for safety's sake the torus is divided into three residential areas separated by three agricultural areas. The latter is segmented into controlled zones which may be completely closed off from other zones. This arrangement permits farmers to use higher than normal temperatures, carbon dioxide levels, humidity and illumination in the controlled zones to force rapid growth (fig. 5-10). Partitioning also inhibits the spread of any disease of plants or animals from one zone to another.
A couple of minutes walk brings a view of tiers of fields and ponds and cascading water (fig 5-11). The upper level where you enter is surrounded by a number of ponds holding about 90,000 fish. There are similar ponds in the other two farms. From the ponds the water flows down to lower levels where it irrigates fields of corn, sorghum, soy beans, rice, alfalfa, and vegetables, and provides water for livestock. The multiple tiers triple the area of cropland (fig 5-12).
On the second tier down a farmer shows you around. The wheat growing on this tier, he tells you, will be ready for harvesting next week. Each of the three agricultural areas in the colony grows essentially the same crops; however, harvests are staggered to provide a continuous supply. On another tier enormous tomatoes grow in a special control zone with elevated levels of carbon dioxide, temperature, and humidity. On one of the lower levels, the farmer impresses you with the fact that this farm, like the others, contains some 20,000 chickens, 10,000 rabbits, and 500 cattle. The lowest level is enclosed and kept at very low humidity to permit rapid drying of crops to hasten produce flow from harvest to consumption. Because of its high productivity the colony's agriculture feeds 10,000 people on the produce of 61 ha (151 acres). You marvel that so fruitful a garden spot is actually in barren space, thousands of miles from any planet.
The agricultural system supplies an average person of 60 kg with 2450 cal (470 g of carbohydrates and fats and 100 g of protein) and almost 21 of water in food and drink each day (ref. 2). Plants and animals are chosen for their nutritional and psychological importance (ref. 3) (e.g., fresh fruits, vegetables, and beef). The principal crop plants and animals and the areas devoted to each are given in tables 5-4 and 5-5.
TABLE 5-4 (gif format)
| Amount required, g/person/day | Yield, g/m^2 /day |
Area, m^2 /person | |
|---|---|---|---|
| Sorghum | 317 | 83 | 3.8 |
| Soybeans | 470 | 20 | 23.5 |
| Wheat | 225 | 31 | 7.2 |
| Rice | 125 | 35 | 3.6 |
| Corn | 50 | 58 | .9 |
| Vegetables | 687 | 132 | 5.2 |
| Totals | 1874 | 359 | 44.2 |
| Animal | Number/ person | Area/ animal, m^2 | Area/ person, m^2 |
|---|---|---|---|
| Fish | 26 | 0.1 | 2.6 |
| Chickens | 6.2 | .13 | .8 |
| Rabbits | 2.8 | .4 | 1.1 |
| Cattle | .15 | 4.0 | .6 |
| Total | - | - | 5.1 |
Fruit is not included in these tabulations. The trees are grown in residential areas and parks where they provide beauty as well as fruit. The crops are grown in a lunar soil (ref. 4) about 0.3 m deep. This soil is made into a lightweight growth matrix by foaming melted rock. The yields are greater than those achieved on Earth because of improved growing conditions and the ability to grow crops on a year-round basis. The higher levels of carbon dioxide, improved lighting, and temperature and humidity control increase productivity to approximately 10 times that of the typical American farm. Terrestrial experiments ( ref. 5) have produced fivefold increase in yield for production of vegetables in controlled greenhouses. (For more details on the agricultural system, see appendix C.)
Life Support Systems
Next stop on your tour is the waste processing facility at the bottom of the agricultural area. It is an important part of the life support system because it maintains a delicate balance between the two opposing processes of agricultural production and waste reduction A sanitation technician explains the operation of the facility.
He points out that on Earth production and waste reduction are balanced, at least partly, by natural processes. Water is extracted from the atmosphere by precipitation as rain; biodegradable materials are reduced by bacterial action. In space neither of these processes is fast nor reliable enough. The colony, lacking oceans and an extensive atmosphere in which to hold wastes, is limited in its capacity for biomass and cannot duplicate Earth's natural recycling processes. Instead, it uses mechanical condensation of atmospheric moisture and chemical oxidation of wastes to reduce the recycling time to 1-1/2 hr. This approach minimizes the extra inventory of plants and animals necessary to sustain life and to provide a buffer against breakdowns in the system.
Agriculture uses sunlight, carbon dioxide, and chemical nutrients to produce vegetation and from that, to raise animals Oxygen and water vapor released as byproducts regenerate the atmosphere and raise its humidity. A considerable amount of vegetable and animal waste is produced along with human wastes of various kinds - sewage, exhaled carbon dioxide, and industrial byproducts - and all these have to be recycled
Waste processing restores to the atmosphere the carbon dioxide used up by the plants, reclaims plant and animal nutrients from the waste materials, and extracts water vapor from the atmosphere to control the humidity of the entire habitat and to obtain water for drinking, irrigation, and waste processing. He tells you that balancing waste generation and waste reduction is a major accomplishment of the designers of the colony, for it eliminates any need to remove excess wastes from the habitat thereby avoiding having to replace them with expensive new material from Earth.
The technician explains that water is processed at two points in the system. Potable water for humans and animals is obtained by condensation from the air. Because evapotranspiration from plants accounts for 95 percent of the atmospheric moisture, most dehumidifiers are located in the agricultural areas. Because of the rapidity with which plants replace the extracted water it is important that the dehumidification system be reliable. Otherwise the air would quickly saturate, leading to condensation on cool surfaces, the growth of molds and fungi, and an extremely uncomfortable environment. Several subunits are used for dehumidification.
The dehumidifiers work in conjunction with the heat exchange system which carries excess heat from the habitat to the radiator at the hub. For water condensation in the torus' gravitational field, normal condensation techniques are used. Figure 5-13 shows schematically (ref. 6) how water is removed in zero-g areas such as the hub. The humidity is controlled by varying the temperature of the coolant and the rate at which air is passed through the unit. To cool and dehumidify it, the atmosphere must be passed through a thermal processor several times per day.
Water is also a byproduct of the continuous wet oxidation process (ref. 7) shown schematically in figure 5-14.
The complete water supply illustrated in figure 5-15 provides 25 times the potable water needed to satisfy the metabolic requirements of the colonists and their animals. (Figure 5-16 considers only metabolic requirements and does not include water for waste transport.) In addition, some 250 kg of recycled water per person per day is used for waste transport. In spite of this extensive dilution, the total per capita water use in the colony is only 75 percent of U.S. domestic water usage. Consumption is limited by use of recirculating showers, low volume lavatories, and efficient use of water in food preparation and waste disposal. Any increase in water for waste transport reduces the amount of condensed atmospheric water which can be used for irrigation, and increases the recycle water. In addition, 200 kg/person of water is set aside for emergencies and fire protection.
Water condensed from the air is heated to 16 degrees C and fed into the fish ponds. After flowing through the ponds, the water is continuously screened to remove fish waste, mixed with warm recycled waste water, and used for irrigation. Since the water drains through soil and collects under the "field" it is further used to transport animal and human wastes to the waste processing facility.
The temperature difference of the influent and effluent for waste processing is 34.5 degrees C. Heat exchangers are used with the cool, condensed atmospheric water and the recycled water to reduce the cooling necessary for recycled water to 22.2 MJ/person/day. (See fig.5-17.)
In addition to water the wet oxidation process produces exhaust gases rich in carbon dioxide which are scrubbed to remove trace contaminants. The carbon dioxide is fed into the agricultural areas to maintain high concentrations and improve agricultural yields. Solids in the effluent are filtered and returned to the system as animal feed and fertilizer. A high concentration of solids is desirable to make the wet oxidation reaction self sustaining; that is, the difference in temperature between the effluent and influent depends upon the concentration and heat value of the solids. The balance between mass input and output to permit the life support system of the colony to operate in a closed loop is shown in figure 5-16.
The flow of energy in the colony is of major importance since energy is required both for production of manufactured goods and for agriculture, and the waste heat must be removed by radiators. In addition, industrial processes and the normal amenities of life (e.g., stoves, refrigerators, and other appliances) require electrical energy, the heat of which must also be removed.
Within the habitat itself the largest energy input is the insolation of the agricultural areas (the bulk of which is transferred to water evaporated from the foliage) and the residential areas (see fig. 5-18). A smaller but significant portion of the total input is the electrical power supplied to the colony from its solar-electric power station. The habitat's electrical power consumption per capita is 3 kW, a figure obtained by doubling that of the current U.S. per capita consumption to account for the need to recycle all materials in the colony.
The energy removed from the atmosphere is transferred to the working fluid of the radiator. Assuming a radiator temperature of 280 K, corresponding to a black body radiation of 348 W/m^2, the required area of a 60 percent effective radiator is 6.3 X 105 m^2 . An increase of 50 percent in the area to handle peak daytime solar loads is appropriate; therefore, the required area is 9.4 X 105 m^2. Woodcock's estimate (ref. 10) of 2.5 kg/m^2 for the mass of a radiator leads to the habitat requiring 2400 t of radiator mass.
Stopping for a mug of Space Blitz on the way back to your apartment you happen to catch the Princeton-Stanford ball game on television from Earth and learn that, to everyone at the bar, the three-dimensional ball game played in the central hub is much more thrilling. You find that really only the name of the game played at the colony is the same since the liberating effects of low gravity and the Coriolis accelerations make all shots longer, faster, and curved, thus completely changing the rules and the tactics of the game.
Later the TV news carries a story on difficulties encountered in building the new SSPS. There have been several unforeseen problems with all phases of the production process but in particular with the extraction facility which, to avoid pollution of heavy industry and to isolate a possible source of industrial accident from the habitat, is placed outside the habitat, south of the hub some 10 km away. Although the plant is operated remotely so that it can be left exposed to the vacuum of space, there are a number of small spheres attached to the plant where maintenance can be performed in a "shirt sleeve" environment. The plant has its own solar furnaces and a 200 MW electric power station run by solar energy. Bulk products such as aluminum ingots, oxygen gas, plate glass, expanded soil and shielding material, are brought to the fabrication sphere by small tugs. However, small items and people make the trip through a pressurized transport tube which seems to be developing structural problems near its remote end. In the bar, a construction foreman tells you he is convinced the problem derives from torsional fatigue, but no one seems to be worried since many such problems in the system have been quickly solved in the past. On learning you are a newcomer the foreman offers to act as guide on a quick visit to the fabrication facilities where the major effort of the colony is concentrated and, if possible, down the connecting tube to the extraction plant. Pleading fatigue you head home. At your apartment, you put your feet up and read some descriptive material on the fabrication facilities.
Productivity in Space Construction
Productivity in space is difficult to estimate (see appendix D). The zero g and high vacuum in some situations increases productivity above that obtainable on Earth and decreases it in others. The only basis for estimation is experience on Earth where the models of industrial productivity used are based on factors of manhours of labor per kilogram, per meter, per cubic meter, etc.
Table 5-6 presents estimates of productivity of humans performing some basic operations of industry and construction.
TABLE 5-6 (gif format)
| Industry | Productivity |
|---|---|
| Primary aluminum (Hall process) | 97 kg/man-hr |
| Titanimum mill shapes | 8.8 kg/man-hr |
| Household freezers | 20 kg/man-hr |
| Light frame steel erection | 28.57 kg/man-hr |
| Piping, heavy industrial | 0.26 m/man-hr |
These numbers were derived from estimating factors commonly used on Earth (ref. 8) in 1975, which were modified somewhat on the basis of limited experience in the space program.
Generally, because cost estimating factors are closely guarded proprietary figures in terrestrial industry, reliable information is difficult to obtain. Therefore, the estimates in table 5-6 are used, recognizing appreciable uncertainty in their values. A more detailed discussion of estimated productivity is given in appendix D.
Manufacture of Satellite Solar Power Stations
In addition to constructing new colonies, the manufacture of satellite solar power stations is the second major industry. Such power stations provide the chief commercial justification of the colony. Placed in geosynchronous orbit they satisfy the Earth's rapidly increasing demand for electrical energy by capturing the energy streaming from the Sun into space and transmitting it to Earth as microwaves where it is converted to electricity and fed into the power grids. While such satellite power stations could be built on Earth and then placed in orbit ( refs. 9 and 10), construction in space with materials from the Moon avoids the great expense of launching such a massive and complex system from Earth to geosynchronous orbit. The savings more than offset the higher costs of construction in space.
Analysis shows that 2950 man-years are needed to build a satellite solar power station to deliver 10 GW to Earth. A summary of the man-years required for different options for constructing part of the system on Earth and part in space, or for using a photovoltaic system rather than a turbogenerator, is given in table 5-7.
TABLE 5-7 (gif format)
| Labor, man-years | |
|---|---|
| Thermal SPSS, 10 GW Complete SPSS | 2950 |
| Generator (SPSS w/o transmission) | 1760 |
| Heating furnace only | 1600 |
| Photovoltaic SPSS, 5 GW Complete SPSS | 2540 |
| Generator (SPSS w/o transmission) | 1800 |
Other Commerce
There are commercial activities of the colony other than those of constructing satellite solar power stations or new colonies. The easy access to geosynchronous orbit from L5 puts the colonists in the satellite repair business. Communications satellites, which otherwise might be abandoned when they fail, can be visited and repaired. Furthermore, the solar power stations themselves require some maintenance and may even have crews of from 6 to 30 people who are periodically rotated home to L5.
There are also commercial possibilities only just being appreciated. In high vacuum and zero g adhesion and cohesion effects dominate the behavior of molten material. Products such as metal foams and single crystals are more easily made in space than on Earth. In fact in 1975 McDonnell Douglas Astronautics Company (ref. 11) concluded that the growing of single-crystal silicon strip using an unmanned space factory would be economically advantageous.
Certain features are common to all commercial ventures in space. High cost of transportation makes shipment of goods to Earth from space uneconomical except for products with a high value per unit mass that are impossible to make on Earth. Advantages of high vacuum and reduced weight often enhance productivity. Availability of large quantities of low-cost solar energy permits production processes in space which consume such large amounts of energy that they are impractical on Earth. The expense of providing human workers encourages reliance on automation which, because of the expense of repairs and maintenance, is pushed to extremes of reliability and maintainability. The expense of replacing lost mass places strong emphasis on making all production processes closed loops so that there is very little waste.
Extraction Processes for Lunar Ores
Production at L5 is strongly influenced by the processes available by which to refine needed materials from the lunar ores. These processes in turn specify the mass of ore required, necessary inventories of processing chemicals, and masses of processing plant.
Figure 4-25 depicts the sequence of processing to produce aluminum from lunar soil. The soil is melted in a solar furnace at a temperature of 2000 K then quenched in water to a glass. The product is separated in a centrifuge and the resultant steam condensed in radiators.
(Table 5-8 lists the process radiators and their sizes.) The glass is ground to 65 mesh and leached with sulfuric acid.
TABLE 5-8 (gif format)
| Process | Temperature, K | Power, MW | Area, m^2 X 10^3 |
Mass, t |
|---|---|---|---|---|
| Quench | 363 | 20.9 | 24.0 | 144 |
| Acid leach | 363 | 7.1 | 8.1 | 49 |
| Acid cooking | 363 | 38.3 | 44.0 | 262 |
| Leach water | 283 | 7.9 | 21.8 | 131 |
| Chlorination | 1123 | 10.1 | .6 | 4 |
| Electrolysis | 973 | 23.1 | 2.6 | 15 |
| Carbon reform | 1123 | 19.8 | 1.3 | 8 |
| Total | --- | 127.2 | 102.4 | 613 |
The pregnant solution containing aluminum sulfate is separated from the waste material in a centrifuge and then autoclaved at 473 K with sodium sulfate to precipitate sodium aluminum sulfate. This separation again requires centrifugation. The precipitate is calcined to yield alumina and sodium sulfate, the latter washed out with water and then the hydrated alumina cabined and coked. The mixture of alumina and carbon is reacted with chloride to produce aluminum chloride and carbon dioxide. The aluminum chloride is electrolyzed to yield aluminum. The melt-quench process with acid leaching was studied and experimentally demonstrated by the U.S. Bureau of Mines (ref. 12). The carbochlorination and electrolysis processes were developed and patented by the Aluminum Company of America (refs. 13-17).
The following four tables (5-9 to 5-12) present the logistical requirements of a processing plant capable of producing about 150 t/day of aluminum, that is, about 54 kt/yr.
The electrical requirements of the system are summarized in table 5-9, while the solar heating requirements are given in table 5-10.
TABLE 5-9 (gif format)
| Process | Power, MW |
|---|---|
| Electrolysis | 70 |
| Carbon reform | 40 |
| Other | 5 |
| Total | 115 |
TABLE 5-10 (gif format)
| Process | Power, MW | Temp, K | Mirror projected area, m^2 X 10^3 |
|---|---|---|---|
| Melt | 27 | 1973 | 19 |
| Autoclave | 32 | 473 | 23 |
| Decomposition | 12 | 1173 | 9 |
| Calcination | 5 | 1073 | 5 |
| Totals | 76 | - | 56 |
Table 5-11 indicates the mass inventory for process chemicals as determined by detailed evaluation of the flow chart. The equipment masses were determined through discussion with industrial contacts.
TABLE 5-11 (gif format)
| Chemical | Mass, t | Mass excluding oxygen, t |
|---|---|---|
| H2O | 225 | 28 |
| H2SO4 | 55 | 19 |
| Na2SO4 | 30 | 17 |
| NaCl | 235 | 235 |
| LiCl | 70 | 70 |
| Cl2 | 25 | 25 |
| Carbon | 2 | 2 |
| Totals | 642 | 396 |
The mass of the entire system is presented in table 5-12.
TABLE 5-12 (gif format)
| Item | Mass, t |
|---|---|
| Structure | 500 |
| Chemicals | 650 |
| Equipment | 3000 |
| Radiators | 600 |
| Flare shield | 50 |
| Solar furnace | 20 |
| Powerplant | 2800 |
| Total | 7620 |
Tired of reading the technical literature, you still find it difficult to fall asleep in this new world which is so much like Earth superficially yet completely man-made. It is clear that this space colony of people with new life styles, interests and visions of the future is still tied to the Earth economically. You decide that it is, in fact, the commercial activities of the colony and economic relations to Earth which explain several of the striking features of life at L5. Long term economic self-sufficiency and growth require manufacture of products suffeiently useful to Earth to attract capital and, ultimately, to create a favorable balance of trade in which the value of exports exceeds that of imports. While great effort is concentrated on construction of solar power plants and new colonies, the colonists also seek to minimize imports by producing goods for internal consumption and by maintaining a major recycling industry. The conflict between using resources and manpower for production for internal use and using them for production for export calls for many management decisions. In these early years of the colony the balance seems to be definitely in favor of production for export. Consequently, reliance on Earth as a source of the products and services of highly developed technology as well as for carbon, nitrogen, and hydrogen continues to be great. Moreover, concentration on exports greatly limits the diversity of human enterprise in the colony, because the majority of productive workers are engaged in heavy construction. Like most of the frontier communities in history, the colonists at L5 are chiefly concerned with repaying borrowed capital, increasing their standard of living, and expanding their foothold to develop further their mastery over the environment of space.
Finally, you drift off in sleep, dreaming of yourself as an early American pioneer, clearing a small stand of trees for your new farm.
After several days of touring the colony you have been continually reminded of the role of the Moon. The soil in which food is grown came from the Moon. The aluminum used throughout the colony for construction once was part of lunar ore. Even the oxygen you breathe has been extracted from lunar rocks. During the construction of this colony 1 million tonnes of lunar ore were shipped each year, and the colony still processes roughly the same amount annually to construct new colonies and satellite solar power stations.
The mining and transport of this material on and from the Moon is a major part of a successfully functioning system for space colonization. You accept an invitation to travel to the Lunar Base, and start at the module at the colony's North Pole where you board an IOTV carrying supplies to the Lunar Base. The same type of transport vehicle brought you from low Earth orbit to L5 in 5 days; however, it takes about 2 weeks to reach the Moon from L5.
The Site of the Lunar Base
When the IOTV has entered lunar parking orbit, it is joined by a smaller ship known as the LLV (lunar landing vehicle). You transfer to it through a docking port and then the LLV descends to the lunar surface in a few minutes and settles gently down with the retrorockets creating a huge cloud of dust which settles back to the surface quickly in the absence of any atmosphere. You have arrived at the Lunar Base. (For more information concerning the impact on the lunar atmosphere, see appendix G.)
You join several off-duty staff members in the lounge of the lunar base for a snack and a cup of coffee. The base provides many services to the people operating on 2-yr tours of duty. These services include recreational facilities, private apartments, and an excellent dining hall - to make their stay as pleasant as possible. Living conditions at the lunar mining base, while comfortable, reflect those of a work camp rather than a family habitat. The base is a monolithic structure composed of prefabricated units. It is covered with lunar soil 5 m deep to protect it against meteorites, thermal fluctuations, and ionizing radiation.
Since primary activities here are mining ore, compacting the ore and launching it to L2 (the base also supports exploration and research efforts), you are anxious to see the facilities. Walking in the Moon's weak gravitational field is so effortless that you are quite willing to don a spacesuit and join the base commander in a walking tour outside the pressurized area of the base.
Mining and Processing Ore for Shipment
Soon you arrive at the edge of a large hole in the lunar surface which is now almost 2 km across and 10 m deep, from which the ore is scooped. The base commander explains that to supply the I million tonnes per year to L5 a surface area the size of about 8 football fields must be mined each year. The mining machinery operates 50 percent of the time, requiring a mining rate of about 4 t/min (about 1 m^3/min). Soil is scooped and carried to the processor by two scooper-loaders (refs. 18-20). Ore is carried from the mining area on a conveyor system. At the launch area it is compacted to fit into a launcher bucket, and then fused.
The site for the base is in the Cayley area at 4 degrees N. 15 degrees E. where Apollo 16 landed. This site was selected because of richness of lunar ore, suitably flat terrain for the launcher, and the near-side equatorial region gives a suitable trajectory to L2. Apollo samples had an aluminum content between 4.5 and 14.4 percent, the highest percentage being from this site. The Apollo missions did not provide any evidence of rich ore veins below the lunar surface.
Lunar bases have been the subject of many design studies (refs. 18-20). The total mass of housing and life support equipment is approximately 2000 t brought from Earth to accommodate the construction crew of 300 persons. During the mining operations, there are only 150 persons at the base of whom approximately 40 are support personnel. Consumables of 495 kg (including 0.45 kg for losses) per person-day are supplied from Earth. The mass imported each year is given in table 5-13.
TABLE 5-13 (gif format)
| Imports | Mass, t/yr |
|---|---|
| Crew consumables | 270 |
| Maintenance supplies | 100 |
| Crew rotation* | 14 |
| Atmosphere leak replacement | 18 |
| Total | 402 |
Almost all activities are in a "shirt sleeve" environment within the shielded structure. A large area is provided for repair work. The mass and power required for these operations on the Lunar Base are summarized in tables 5- 14 and 5-15.
TABLE 5-14 (gif format)
| System | Mass,t |
|---|---|
| Mining and conveyor system | 250 |
| Housing and life support | 2,400 |
| Technical Support | 500 |
| Launcher | 4,000 |
| Power plant (200MW + 10%) | 9,900 |
| Total | 17,050 |
TABLE 5-15 (gif format)
| System | Power MW |
|---|---|
| Launcher | 192.00 |
| Mining | 0.70 |
| Compaction | 7.15 |
| Living quarters | .15 |
| Total | 200.00 |
The Mass Launcher
Critical to the success of the entire system of colonization of space is the ability to launch large amounts of matter cheaply from the Moon. There are two aspects: launching the material from the Moon by an electromagnetic launcher using the principle of the linear induction motor, and gathering the lunar material in space by an active catcher located at L2.
Each second the mass launcher accelerates five 10-kg masses of lunar material to lunar escape velocity of 2400 m/s. Errors in launch velocity are kept within 10^-4 m/s along the flight path and 10^-3 m/s crosswise to it.
The masses are carried in an accelerating container or "bucket." Built into the walls of each bucket are liquid helium-cooled superconducting magnets which suspend it above the track. The buckets are accelerated at 30 g over 10 km by a linear electric motor running the length of the track. The bucket then enters a drift section of track, where vibrations and oscillations lose amplitude enough for the payload to be released with great precision of velocity. The velocity of each bucket is measured, and adjusted to achieve the correct value at release.
During acceleration the payload is tightly held in the bucket, but when lunar escape velocity is reached and the velocity is correct the payload is released. Since the bucket is constrained by the track to follow the curve of the lunar surface, the payload rises relative to the surface and proceeds into space. Each bucket then enters a 3 km region where a trackside linear synchronous motor decelerates it at over 100 g. It is returned to the loading end of the track along a track parallel to the accelerator.
At the load end of the track the liquid helium used to cool the superconducting magnets is replenished, and a new payload loaded. Then the bucket is steered to the start of the accelerator for another circuit. Figure 5-19 (overleaf) shows the mass launcher schematically. More details are given in appendix F.
With a 70 percent duty cycle, this system can launch 1.1 Mt/yr. To assure this duty cycle during lunar night as well as lunar day, two complete mass launchers are necessary. A nuclear power plant rather than a solar plant is required so the operation can continue through the lunar night.
Power and Supply
Several nuclear reactor single-cycle helium-Brayton plants of 10 to 50 MW each are used instead of a single big plant because the smaller plants can be transported assembled and become ready to operate by use of space shuttle main engines. The redundancy of several smaller systems is attractive, especially since the plants need to be taken off-line for refueling every year or two.
The total capacity is 220 MW and the total mass is 9900 t, including a 10 percent design factor.
The mass of the power plant is estimated using the value of 45 t/MW, which is projected to be applicable to nuclear plants within the decade 1. Shielding will be provided by lunar material.
The problem of collecting the stream of material launched by the mass-driver is solved by a kind of automated "catcher's mitt, " the mass catcher, located at L2. Although the catchers are fully automated there is a 2-person space station at L2 for maintenance personnel. This station is adequately shielded against possible hits by stray payloads.
Because it would be dangerous to navigate in the vicinity of the catcher while the launcher is operating, you are not able to visit the catcher personally. Instead you learn about it from an operator who is at the Moon base on recreation leave.
He tells you that the mass catcher is an active device to capture payloads of lunar material shot by the mass launcher. The payloads are solid blocks 0.20 m in diameter, made of compacted and sintered lunar soil. Each payload has a mass of 10kg and arrives at L2 with a speed of 200 m/s.
The catcher is in the form of a thin, light net, 10 m^2 in area, which is manipulated by three cables to position the net anywhere within an equilateral triangle. The cables are wound on reels which move on three closed loop tracks Each side of the equilateral triangle is 1 km, thus providinga 0.43 X 106 m^2 catch area The total mass of the catcher is 220 t.
Station-Keeping With the Rotary Pellet Lanucher
You learn that the mass catcher uses an unusual propulsion device - a rotory pellet launcher - to position the catcher so that it is always facing the incoming stream of payloads Furthermore, this device provides a counterthrust to the force of some 2000 N imparted to the catcher by the stream
Further details of the mass catcher are provided in appendix G. and because of their importance the trajectories from the Moon to L 2 and their relation to station-keeping are described in appendix H. The mass catcher is illustrated in figure 5-20.
The rotary pellet launcher is a heavy tube rapidly rotating to accelerate and eject small pellets of rock. (See fig. 5-21).
Velocities as high as 4000 m/s may be attained, equal to the exhaust velocities of the best chemical rockets. The pellets themselves are sintered or cast directly from lunar rock, with no chemical processing required. The launcher uses 5 percent of the mass received as propellant. (For further analysis see appendix I.)
This rotary pellet launcher is mechanically driven by an onboard nuclear power system rated at 20 MW. The power plant radiator is situated in such a manner as to radiate freely to space while being shielded from impacts of stray masses. The inner surface of-the radiator is insulated and made highly reflective, so as to avoid heating the catcher.
The transport of lunar material from the catcher to the colony is accomplished using a space ore-carrier. The trip from L2 to L5 requires some 2 months. The rotary pellet launcher is the primary propulsion system since a thrust of only several thousand newtons must be obtained over a period of weeks to perform the mission. Of course, the rotary launcher cannot be used in the vicinity of either the colony or the mass-catcher, because of the danger from its exhaust of high-velocity pellets. For low-velocity maneuvers in these vicinities chemical rockets can he used.
You express concern to the operator of the mass catcher over the possible hazard of using high velocity pellets as propellant mass because they constitute artificial meteoroids They are ejected with high velocity, not so high as to escape the Solar System, but sufficiently high to escape the Earth-Moon system and take up solar orbits. Typically, they will range inward as far as Venus and outward to Mars' orbit.
The operator's response is reassuring. He reminds you that the astronomer George Wetherill (ref. 21) studied the lifetimes of meteoroids in such orbits, or the times before collision with Earth He found a mean lifetime of 10^7 years. The Earth presents a surface area of 5 X 108 km^2, while a colony's area is some 1 km^2 or less, and a spacecraft's area much less. Using a standard that no more than one impact from a pellet per square kilometer every 10 yr may be allowed, then 5 X 10^14 pellets may be permitted to orbit the Sun following ejection. If each has a mass of 10g, the allowed mass of ejected pellets is 5 X 10^9 t. This is some 10,000 times the mass of pellets to be ejected in the course of carrying material for building the colony. He assures you that the rotary pellet launcher will be a useful propulsion system for many years, before the environmental effect of ejected pellets becomes noticeable in comparison to the effect of meteoroids naturally present in space.
It is now 2 months since you left Earth. In that time you have traveled over 750,000 km, you have another 386,000 to go to get home to Earth. You have seen a tiny community of 10,000 men and women crowded into the colony and in small bases on the Moon and at L2 separated by vast distances which are in turn dwarfed by the immensities of space. Homesickness is inevitable. It is time to leave the realms of the colonists. Their tasks and their will to do them are enormous, and only those people can be colonists who have a large capacity to work hard and long when, as soon happens, tedium replaces the initial excitement. You speculate that it will be mostly their children and grandchildren who will master space. The great mass of mankind will remain in the cradle of Earth; only a few will go into space.
You are fortunate to get a berth in one of the ships that brings supplies to the Moon and rotates personnel from the Moon base directly back to Earth In the early years all the men and women of the base went straight back to Earth and so the personnel transporter was full to capacity. Now increasing numbers choose to spend their rotation time at L5 instead of on Earth and berths are available on the run to Earth. You wonder whether this seed of human society planted in such an unlikely environment will flourish, and settling back into your seat to read a terrestrial news magazine you conclude that only time will tell.
