TABLE 4-8 — WALL CONSTRUCTIONS
| System | Construction | | :--- | :--- | | Exterior wall system | Cellular silicone glass (10 cm) with 22 ga aluminum skin on each side, 191 Pa (4 $lb/ft^2$) or 2.5 cm aluminum honeycomb with 5 cm silicone foam glass and 22 ga aluminum skin on one side, 164 Pa (3.5 $lb/ft^2$) | | Interior wall system | 5 cm aluminum honeycomb with 22 ga aluminum skin on both sides, 120 Pa (2.5 $lb/ft^2$) |
For floor and roof systems the lightest constructions generally available on Earth are composed of light, open-web framing, suspended ceilings, and metal floor decking. This is chosen for the baseline. Stressed skin panel construction made from aluminum web members and aluminum skin is also light and therefore a viable alternative. For a 9 m span and residential live loads (unreduced) of 1.9-2.9 kPa (40-60 $lb/ft^2$), the dead loads for each of these systems are given in figures 4-21 and 4-22.
Figure 4-21 — Alternative floor system — “stress skin.”
<!-- image -->² NASA general working paper MSC-01-542 A Preliminary Structural Analysis of Space-Base Living Quarters Modules to Verify a Weight Estimating Technique, p. 45.
Figure 4-22 — Baseline floor system.
<!-- image -->APPENDIX G: POPULATION DISTRIBUTIONS AND TRENDS
The U.S. population as described in the 1970 Census is used as a basis from which the colony properties are derived. The sex ratio is increased by about 10 percent in favor of the males and it is assumed that there is a substantial shifting of the population out of the more dependent ages — from under 20 and over 45 — into the 21-44 age class. Other assumptions include an increase in the participation of married women in the labor force and some fairly serious adjustments in the marital status distribution, all of which are directed toward increasing the proportion of the population in the effective work force. These data are shown, with some comparable statistics for the United States, in tables 4-9 to 4-13.
From the numbers in table 4-14, it is apparent that systematic differences as to the proportions of the labor force engaged in production for export exist among U.S. communities of varying size. At a minimum, the percentage of workers engaged in work pertaining to the internal functioning of the community is approximately 30 percent, leaving 70 percent for export industry and for those who, by industrial standards, are not considered productive. These approximations are modified slightly to reflect features of early settlement, including a somewhat higher proportion of workers in internal activities. Table 4-15 shows the population development and the percentages of workers engaged in export activities for the first 14 yr following the beginning of construction.
TABLE 4-9 — AGE DISTRIBUTION
| Age Group | U.S. 1970 (%) | Colony (%) | | :--- | :--- | :--- | | 0-20 | 39.6 | 10.0 | | 21-44 | 31.7 | 80.0 | | 45+ | 28.7 | 10.0 |
TABLE 4-10 — SEX RATIOS (Males per 100 females)
| Age Group | U.S. 1970 | Colony | | :--- | :--- | :--- | | All Ages | 94.8 | 110.0 |
TABLE 4-11 — PERCENT EVER-MARRIED BY SEX AND AGE
| Age Group | Male (Colony) | Female (Colony) | | :--- | :--- | :--- | | 21-44 | 85.0 | 90.0 |
TABLE 4-12 — LABOR FORCE PARTICIPATION RATES BY AGE AND MARITAL STATUS — U.S: 1970 AND INITIAL COLONY ASSUMPTIONS
| Group | U.S. 1970 (%) | Colony (%) | | :--- | :--- | :--- | | Males (21-44) | 90.0 | 95.0 | | Females (21-44, Married) | 40.0 | 70.0 | | Females (21-44, Single) | 75.0 | 85.0 |
TABLE 4-13 — POPULATION DISTRIBUTION BY AGE, SEX, AND MARITAL STATUS — INITIAL COLONY SETTLEMENT
| Age | Male | Female | Total | | :--- | :--- | :--- | :--- | | 0-20 | 525 | 475 | 1000 | | 21-44 | 4200 | 3800 | 8000 | | 45+ | 525 | 475 | 1000 | | Total | 5250 | 4750 | 10000 |
TABLE 4-14 — MINIMUM PERCENTAGES EMPLOYED IN 14 INDUSTRY CLASSIFICATIONS IN AMERICAN COMMUNITIES OF VARYING SIZE, 1960 AND 1950
Source: E. L. Ullman (1971) The Economic Base of Cities. Seattle: University of Washington Press.
TABLE 4-15 — POPULATION AND LABOR FORCE DEVELOPMENT — THROUGH THE 14TH YEAR FROM THE BEGINNING OF COLONY CONSTRUCTION AT L5
| Year | Population | Labor Force | Export Workers | % Export | | :--- | :--- | :--- | :--- | :--- | | X+10 | 4300 | 3200 | 2000 | 62.5 | | X+14 | 10000 | 7200 | 4400 | 61.1 |
- a Labor force participation rates would be expected to decline to approximately U.S. levels eventually. Export activity as a proportion of total labor force assumed to resemble those found in U.S. communities of comparable size (after E. Ullman and others, 1971, The Economic Base of Cities, Seattle: University of Washington Press).
- b X denotes the year in which colony construction begins.
APPENDIX H: SATELLITE SOLAR POWER STATIONS (SSPS)
A geosynchronous orbit is on the Earth's equatorial plane with a radius at which a satellite matches the Earth's angular velocity, and is stationary with respect to an observer on the Earth's surface. This orbit lends itself to communications, monitoring of the Earth's surface, and power transmission to the Earth's surface, all of which need to be done more or less continuously without interruption of service.
The power transmission concepts call for the collection of solar power by huge satellites, conversion to electrical power by either photovoltaic (ref. 34) or thermal methods (ref. 35) and transmission to the Earth by 10 cm microwave power beams (ref. 36). On the Earth's surface the power is to be received, rectified and then fed into the power grid.
The photovoltaic conversion satellite concept (see fig. 4-23) (under study by a group of companies headed by Arthur D. Little, Inc.) takes the incoming sunlight, which has an energy flux of almost 1.4 $kW/m^2$, concentrates it by a factor of 2 onto thin silicon solar cells, and beams 8 GW of power to Earth with an assumed dc to dc efficiency of 65 percent resulting in a received power of 5 GW. Studies presently indicate a mass/power ratio of 3.6 kg/kW for this satellite (ref. 37).
In the thermal conversion concept (under study by Boeing) 10,000 individually-steered facets concentrate the sunlight by a factor of 2000 into a cavity (personal communication with Gordon Woodcock, Boeing). In the cavity the sunlight heats helium which, in turn, drives Brayton cycle turbogenerators. The low end of the cycle is a large radiator operating at 550 K. (The model for the cycle and turbogenerators is a 50 MW plant in Oberhausen, Germany which uses a closed cycle with helium as a working fluid.) Four independent sections, each with 1 cavity, make up this SSPS. The power transmission is the same as for the photovoltaic SSPS. Studies indicate a specific mass of 6.5 kg/kW for 10 GW output received on Earth (ref. 35).
A solar power satellite built at the colony is transferred to geosynchronous orbit, requiring several months to complete the journey. Once in place the 5-20 GW system's output is tied into the terrestrial surface power grid to provide relatively cheap electricity to Earth.
Figure 4-23 — Photovoltaic SSPS.
Image
A photovoltaic SSPS is expected to require little maintenance. Periodically, to overcome radiation damage, the solar cell arrays have to be annealed by heating them perhaps 50° C above ambient operating temperature; this is done automatically by the satellite. Failure of such parts as amplitron tubes and solar blankets, and the inevitable but infrequent hits by small meteoroids require repairs. A "smart" machine replaces parts on the transmitting antenna and the solar cell blankets, but repair of structural damage requires several people to help the "smart" machines.
It is desirable to do as little maintenance of solar power satellites as possible with people because the structure is not designed to provide life support for them. Also, the huge size of the satellite makes the amount of work one person can do negligible compared to a machine. For maintenance of a 5-20 GW photovoltaic power satellite a crew of less than 6 people is projected. For a thermal conversion power satellite more people are needed since there are more moving parts, but a crew of less than 50 is enough for a 10 GW satellite. The repair crew is housed in a small shack or "caboose" near the center of the satellite and rotated periodically to the habitat.
Because the satellite is a cheap stable orbital platform in sight of Earth all the time it also has on it packages of Earth-sensing instruments, direct broadcast TV stations, and communications links. Most of this equipment is located near the "caboose," so that the maintenance crew can take care of these units as well.
The major force on an SSPS is the gravity gradient torque. The amount of propellant required for station keeping depends upon the satellite's mass distribution and upon the station-keeping strategy adopted.
APPENDIX I: PROCESSING OF METALS
Methods for Refining Titanium
Figure 4-24 demonstrates various means for obtaining titanium from lunar ore. It is reasonable to expect that ilmenite could be obtained from lunar ore since a similar process on terrestrial ore is carried out commercially using a combination of magnetic, electrostatic and flotation separators. This requires crushing, gravity and a flocculant which lead to complicated but not insurmountable problems common to any wet-chemistry process. A further complication may be the presence of magnetic glass formed during meteoroid impacts. At the next processing step the use of high temperature reduction of the ilmenite using hydrogen seems preferable.
The alternatives all require the consumption of carbon. On Earth this simply means the expenditure of coke, but in extraterrestrial processing it means that carbon must be recovered from carbon dioxide produced during the reduction or chlorination, which would have to be accomplished by high temperature reduction of the carbon dioxide with hydrogen. Obviously, it would save processing steps and mass if this process is applied directly to the ilmenite. The next processing step shown in figure 4-24 is the reduction of titanium dioxide. The appropriate method appears to be carbochlorination followed by reduction with magnesium to produce molten titanium. Important considerations are that magnesium is present in lunar ore and the production of titanium in liquid form makes continuous automated processing and alloying simpler to achieve.
Methods for Aluminum Extraction
The aluminum in lunar ore is in the form of plagioclase, $(Ca,Na)(Al,Si)_4O_8$, while magnesium and iron remaining after ilmenite removal are in the form of pyroxene, $(Ca,Fe,Mg)_2Si_2O_6$. These are not normal sources of aluminum, magnesium and iron on the Earth because of the difficulty of economically separating the desired materials from association with such a wide variety of other elements. Literature was surveyed, and researchers at Bureau of Mines consulted to discover by what means metals or their oxides could be extracted from low grade ores comparable to lunar soil. Only two processes were found. These can be used to obtain alumina from anorthosite.
Anorthosite is a rock composed of plagioclase feldspar with minor amounts of pyroxene and olivine and is similar to the material found on the lunar surface. Figure 4-25 shows these processes. The method of soda-lime-sinter was eliminated because it consumes lime at a rate six times greater than it produces alumina, thereby requiring a disproportionate increase in plant size. The direct production of metals by electrolysis of molten anorthosite is often proposed, but the results of research have been discouraging. The remaining possibility is the melt-quench-leach process which in extensive laboratory tests has succeeded in recovering over 95 percent of the alumina present in the ore. In this process the ore is melted and then quenched to a glass. It is then treated with sulfuric acid to leach out the alumina component.
Further treatment of the aluminum sulfate follows standard procedures that have been developed for low-grade bauxites and clays. Figure 4-25 indicates that three paths are possible once alumina has been obtained. The Hall Process is unsuitable because it would be extremely difficult to automate, and it consumes its electrodes and electrolyte. The subchloride process is very attractive because of its simplicity. It consists of reacting aluminum chloride with alumina at high temperature to produce aluminum subchloride which later breaks down into aluminum and aluminum chloride. It has not been chosen as the baseline process because a pilot plant at Arvida, Quebec, was shut down when the process reportedly had difficulty on a large scale. The highly corrosive nature of the chloride vapor has been blamed for the failure.³ Of the two remaining processes, carbochlorination followed by reduction with manganese (Toth Process) is a good possibility. However, it is a batch process yielding a granular product which must be removed, melted, and cast, and requires an extra carbon reduction process. The high temperature electrolysis method is continuous and yields liquid aluminum ready for casting into ingots. For these reasons it has been chosen. However, research should take place into the possibility of a melt-quench process (no leach) followed by direct extraction with a subchloride process which, in theory, could reduce the plant mass by approximately 1/2.