NASA SP-413 — SPACE SETTLEMENTS — A Design Study
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4.8 mils by year 70 as shown in figure 6-6 (see also appendix D). The analysis is quite sensitive to the real discount rate (including inflation) which at 10 percent gives a benefit-to-cost ratio of 1.02. If the discount rate is lowered to 8 percent, the benefit-to-cost ratio is 1.5 (see appendix G).
Still Other Alternatives The date at which a second-generation shuttle system becomes available is important. If development started at year 3 instead of year 15, the benefit-to-cost ratio could be increased to 1.3 and the cost of the program for the initial colony would drop to $112.7 billion, but with greater annual expenditures in the early years of the program. There are alternatives to space colonization for generating electricity from space — building the SSPS’s on Earth, and using construction shacks only without building any space colony. But space colonies win over terrestrial building because they use lunar materials which cost hundreds of times less at the use point in space than do terrestrial materials. While construction shacks cost less and can be built more quickly, in the long run they are more expensive because of their operating costs.
Some Other Energy-Related Benefits While electricity from space and lower costs of electricity to U.S. consumers may be extremely desirable and sufficient to justify a space colonization program, there are other benefits
that have not been fully evaluated in the study but may be significant. Environmentally, microwave transmission of power from space for conversion into electricity at Earth, is a very clean form of energy production (see appendix H). It avoids emission of pollutants into the Earth’s atmosphere and minimizes the waste heat introduced into the terrestrial environment. The conversion of microwave energy to electricity is far more efficient than any thermodynamic process — 85 percent compared with a maximum of 50 percent. Electrical energy from space may also be the only way in which the nation can become energy independent within the same time scale of 70 years, for not only can it supply the needed quantities of electrical energy but also inexpensive electrical energy that might be used for electrolysis of water to produce transportable fuels and thereby reduce dependence on petroleum products in transportation systems. Another subtle energy-related benefit is the widespread nature of its application to mankind. Low-income people spend a comparatively greater percentage of their income on electricity than do affluent people. Thus lower priced electricity would benefit an enormous number of people and not just a few. This benefit from space colonization offers the potential of reaching vast numbers of people in the U.S. and providing relatively low-cost energy to many more in the developing nations of the world. It offers a real alternative to limited growth scenarios for underdeveloped peoples.
TABLE 6-10 — PARAMETERS OF THE COST EQUATION Symbol
Units
Ms O Es Ks Ws Fs Hs Ds R Mm Lm Em Km Hm Fm Nm Dm Y
kg kg/kg/yr kg/kW kW/kg/yr kg/person-yr yr-1 kg/person $/kg kg/person-yr kg kg/kg/yr kg/kW kW/kg/yr kg/person yr-1 persons $/kg yr
Definition Mass of Al in L5 habitat Ratio of L5 plant output/yr to plant mass Specific mass of L5 power plant Power required per unit mass of Al produced at L5 Productivity of L5 workers Crew rotation rate for workers at L5 Mass of L5 construction shack/person Launch costs to L5 Re-supply rate for workers Mass to be launched from Moon Ratio of launcher mass to mass launch rate Specific mass of lunar power plant Power required per unit mass launched from Moon Mass of lunar crew habitat/person Crew rotation rate for workers at Moon Number of crew on Moon Launch costs to Moon Duration of the project — 8 yr
Note — Y is not the duration of the project, but 8 yr less.
Chapter 6 — Building The Colony And Making It Prosper
Baseline magnitude 5 X 108 8.3 14 2.2 X 10-3 46 X 103 1 5 X 103 800 1.7 X 103 1.2 X 1010 4.6 X 10-3 45 2 X 10-4 7 X 103 0.5 150 1600 —