already building, the space-shuttle, and on a simplified shuttle- derived freight rocket. One of the chief difficulties with the ground-launched power-satellite concept is its dependence on massive transport through the atmosphere by launch vehicles more advanced than have ever been built. It has been very difficult to attract large-scale private investment for power satellites, in part because the lift costs for these advanced vehicles are so uncertain. There is further reason for concern about the ground- launched power-satellite concept. In the past we have tended to underestimate the future effectiveness of public opposition to systems viewed as environmentally damaging. There is little question that public opposition has slowed markedly the installation of nuclear electric power. In the ground-launched satellite concept, every powerplant that is established in orbit will require the discharge into the atmosphere of about 20 to 50 times the powerplant mass in combustion products. If satellite power is to be worth its investment, it must be capable of providing the bulk of the new-generator capacity called for at the time of its deployment; if it can only provide a few percent of the national needs it certainly will not attract substantial private investment. To satisfy national needs in the year 2000, even if electric energy demand grows at a rate of only 4%/year, more than a million tons of new power satellites will have to be established in orbit every year. That will require the discharge of roughly 20 to 50 megatons of combustion products per year, into the atmosphere, much of it at high altitudes, where the atmospher is far more
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