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 man-hours 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. 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.
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.
TABLE 5-6 — REPRESENTATIVE PRODUCTIVITIES
| Operation | Productivity (kg/man-hr) | | :--- | :--- | | Aluminum extraction | 100 | | Aluminum fabrication | 20 | | Glass fabrication | 50 | | Habitat assembly | 10 | | Solar power plant assembly | 15 |
TABLE 5-7 — OFF EARTH LABOR REQUIREMENTS FOR SPSS'S
| System Option | Man-years per 10 GW | | :--- | :--- | | Thermal (Space built) | 2950 | | Thermal (Earth/Space mix) | 3500 | | Photovoltaic (Space built) | 2200 | | Photovoltaic (Earth/Space mix) | 2800 |
Notes: Assumes the use of lunar material in productive facilities already in place and high-technology equipment supplied from Earth. The thermal data are based on Woodcock (see ref. 26, ch. 4) and the photovoltaic data on Glaser (see Ref. 25, ch. 4).
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.)
TABLE 5-8 — RADIATORS FOR PROCESS COOLING
| Process | Area (m²) | | :--- | :--- | | Melt-quench | 450,000 | | Leaching | 120,000 | | Calcining | 80,000 | | Electrolysis | 150,000 | | Total | 800,000 |
TABLE 5-9 — ELECTRICAL POWER REQUIREMENTS FOR PRODUCING ALUMINUM
| Operation | Power (MW) | | :--- | :--- | | Grinding | 10 | | Centrifuging | 15 | | Electrolysis | 140 | | Miscellaneous | 35 | | Total | 200 |
TABLE 5-10 — SOLAR HEATING REQUIREMENTS FOR ALUMINUM REFINERY
| Operation | Heat (MW) | | :--- | :--- | | Melting | 150 | | Calcining | 50 | | Total | 200 |
TABLE 5-11 — MASS INVENTORY FOR PROCESS CHEMICALS
| Chemical | Mass (t) | | :--- | :--- | | Sulfuric acid | 1500 | | Sodium sulfate | 800 | | Chlorine | 500 | | Carbon | 400 | | Total | 3200 |
TABLE 5-12 — MASS REQUIRED FOR REFINING
| Component | Mass (t) | | :--- | :--- | | Solar furnaces | 1200 | | Chemical plant | 2500 | | Electrolysis plant | 1800 | | Radiators | 2000 | | Total | 7500 |
The glass is ground to 65 mesh and leached with sulfuric acid. 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 calcined 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 5-11 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. The mass of the entire system is presented in table 5-12.
Relations to Earth
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 sufficiently 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.
THE LUNAR BASE
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 workcamp 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 1 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 m³/min).