The cost estimates of 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. 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. 1 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. The detailed numbers on which these estimates are based 14 are given in a lead article in "Science" which appeared on December 5, 1975. The two most important numbers are the productivity and the interest rate, assumed to be 10% in constant dollars. With inflation that is roughly equivalent to a 17% discount rate as normally quoted by economists. (Fig. 1+2) Because of the high interest rate assumed, the costbenefit analysis is sensitive to the speed of construction of the SMF, and therefore to productivity. The analysis is based on the assumption that productivity in an orbital facility would be no better than for heavy industry on earth. Most of the
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