an annual (new capacity) demand growth of 15 MW/yr, a maximum of 450 MW will be supplied by an SPS satellite if it lasts 30 years beyond its useful life. Since this is but a small percentage of the design power level of the full-scale satellite, it may be concluded that the salvage value derived from this use will be a small percentage of the cost of one full-scale SPS satellite. 4.3 Power Supply for a Laser Orbit-to-Orbit Transportation System As in the case of the demonstration satellite, an interesting potential salvage use of full-scale SPS satellites is as a power supply for a laser orbit-to-orbit transportation system. The economics of this use are quite similar to the demonstration satellite case; however, the full-scale satellite provides some 30 times more power and would thus be appropriate for use with much larger and higher payload vehicles. The benefits of this salvage use are strongly dependent upon geocentric traffic in the post-2030 period. They could be considerable if there are massive manned activities in space, such as large manufacturing bases, space habitats and so on. Alternatively the benefits could be quite small if the traffic remains relatively small. At this point in time the only traffic that would clearly exist beyond that noted in Table 2.1 is the traffic necessary to support the construction and maintenance of the SPS fleet. This traffic, as envisioned by Rockwell International, would involve on the order of 150 POTV flights per year or one every other day. This level of traffic can be supported by a power supply which is on the order of hundreds of megawatts rather than gigawatts. The advantage of a multi-gigawatt system would be to allow higher thrust levels, possibly higher specific impulse and possibly to provide power for ascent from earth-to-LEO. Unless the earth to LEO traffic becomes a major factor, or unless it becomes desirable to station satellites to provide a capability for continuous or unconstrained thrusting, it does not appear that this salvage use will require more
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