transportation costs. At the same time, the demand placed upon a laser space transportation system will be very much higher if the SPS program proceeds into an implementation phase than if it does not. Thus the fact that the SPS program is likely to result in technologies leading to reduced launch costs, and thus to reduce benefits for a laser space transportation system, is substantially offset by the increased traffic that implementation of the SPS would cause. Accordingly the benefits of a laser space transportation system are evaluated using as a baseline the LEO to GEO POTV traffic model identified in Table 2.1. Earth to LEO transportation costs are assumed to be $70 per kg. A second case is also considered using an earth to LEO transportation cost of $800 per kg representative of an advanced Space Shuttle or Shuttle derivative vehicle. To compute a salvage value for this use it is necessary to determine year-by- year savings achieved by the laser space transportation system. To obtain a LEO to GEO traffic model year by year during the period 2000 to 2030, it is assumed that the lower bound of the transportation requirements given in Table 2.1 apply to the year 2000 and the upper bound apply to the year 2030, and that traffic growth between these years is linear as shown in Figure 3.9. The present value of savings obtained by this traffic model, at a 4 percent discount rate, is equal to 83.8 times the year 2000 savings. The present value of the demonstration satellite in this use for the baseline case with transportation costs of $70 per kg is $1.68 billion, and at $800 per kg transportation costs to LEO is $19.27 billion. These numbers, of course, are likely to apply if the SPS program does not proceed into an implementation phase. If the SPS program proceeds into an implementation phase, the benefit from this salvage value would be very much larger. Thus it is clear that it is desirable to devleop and implement the laser space transportation system independent of the SPS program.
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