Table 2. Cost estimates for establishing a first manufacturing facility in space. Cost figures not in parentheses are based on transport rates of $1900/kg from the earth to the lunar surface a.nd $950/kg to Lagrange point LS. Those in parentheses are based on the assumption (/3) of transport rates reduced by a factor of 12, with an additional $10 billion added for vehicle development and no change in administrative costs. In this simplified table, personnel rotation, if required, and material resupply are within the tonnage figures. Ad minisLift to lunar surface Lift to L5 Devel- trative Total Type of estimate Tons $billion Tons Minimal 3,000 5.7 10,000 Intermediate 10,500 20.0 42,000 High 20,000 38.0 80,000 senting that portion of salaries convertible to goods and services on the earth (for subsequent use on visits or; if desired, on retirement), and a carrying charge of 10 percent interest on the outstanding balance in every year of the program (20). That is approximately equivalent to discounted economics with a IO percent discount rate. Cost estimates for the first SMF (Table 2) are based on making an early start, with the shuttle and a shuttle-derived freight vehicle. The lift costs assumed for Table 2 are therefore relatively high, equivalent to $950/kgsy. The time line of Fig. 1 uses the intermediate cost estimate of Table 2. Because of the high interest rate assumed, the cost-benefit analysis is sensitive to the speed of construction of the SMF, 40 20 - 20 Total number of 5000 Mw SSPS stations Years from start of program opment and cost, and con- salaries st ruction (20%) rounded $billion ($billion) ($ bil- ($billion) lion) 9.5 11.0 5.2 31.4 (27.4) 40.0 20.0 16.0 96.0 (50.8) 76.0 40.0 30.8 185 (89.8) and therefore to productivity. The first colony, with a structural mass of about 150,000 tons, is assumed to be constructed in 6 years by a work force of 2,000 people. The corresponding productivity, 13 tons per person per year, is consistent with analyses by D. Morgan of current experience on the earth in materials processing and fabrication (18). I assume that subsequent colonies could be constructed in 2 years. This tripling of production rate would require devoting 4,000 people of a 10,000person colony to new-community construction (compared to 2,000 people available at the construction site during the building of the first SMF) and an increase of efficiency by a modest factor of 1.5. I assume that most of the residents of the 40 Total number of 5000 Mw SSPS stations 10 20 Power cost (mills/kwh) .. .l. '····· 30 Years from start of program Fig. I (left). Estimated costs and benefits of a program for construction of space manufacturing facilities. With assumptions described in the text, the total input capitalization is $178 billion over 14 years, in addition to the costs incurred on the earth for each power satellite produced. Interest of IO percent is paid on the outstanding balance in each year. Power costs, initially 15 mill/kwh, are reduced in steps to achieve market penetration. Fig. 2 (right). Effect of a 7-year delay in the program to wait for advanced lift vehicles~ Although lift costs are assumed to be cut by a factor of 12, the peak funding is reduced by only a factor of 2. Benefits, including energy independence, are delayed by 7 years. 946 early space communities will be employed in production, support services being assisted as far as possible by automation. Later decreases in the employed fraction of the work force are assumed to be compensated by productivity increases. The productivity required at LS for the SSPS would depend on the ratio of kilograms to kilowatts of output at the time of construction. In my assumption, an SSPS supplying 5,000 Mw of electricity at the busbar would have a mass of 80,000 tons; in the study by Woodcock and Gregory (13), 35,000 tons; in the study by Glaser (3), only 11,000 tons. Assuming that the remainder of an SMF work force, 6,000 persons, were committed to SSPS construction, and that two SSPS units were produced per SMF per year, the corresponding requirements for productivity would be 27, 12, and 4 tons per person per year. Most of the production operations of SSPS construction would take place within the weather-free, zero-gravity, enclosed environment of a space community's assembly volume, which should favor high productivity. For 12 to 27 tons per person annually, and a peak production rate of 160 Gw/year of new generator capacity, a total work force of 100,000 to 200,000 people in space would be required. In Fig. I, new colony construction is therefore taken to be halted after the 16th colony, because of market saturation. For the time line of Fig. 1 the benefit/cost ratio would be more than 3. Other time lines, with a variety of input capitalizations, productivities, and interest rates, have also been traced; only extreme cases yield benefit/ cost ratios less than unity. The relative insensitivity of the peak funding requirement to the lift costs assumed can be seen by comparing Figs. I and 2. With the assumptions of Table 2, a reduction of lift costs by a factor of 12 would reduce peak funding by one-half. Because of the exponential growth of the number of SMF's, satellite power could have a strong impact relatively soon. By year 11 from the start of SM F construction, the usable electric energy supplied to the earth by the program could exceed the peak capacity of the Alaska pipeline (2 x 106 barrels a day) (21). Two years later the production rate of SSPS plants could exceed the U.S. annual need for new generating capacity. By year 17, the total energy so far provided from the satellites could exceed the estimated capacity of the Alaskan North Slope (!010 barrels) (21). This discussion has been confined to technical questions. Clearly, though, if an SMF program is initiated, it will have wider impact than the science-oriented space programs that have preceded it. As an enterprise with the potential to return a SCIENCE. VOL. 190
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