earth orbit (LEO) and orbital transfer vehicles (OTV) for transfer of payloads and personnel to geosynchronous orbit (GEO). The system, Grey emphasized, is not a final design. Solar radiation may be converted to electricity by photovoltaic cells, by thermal devices using Brayton or Rankine cycles, or in other ways. The electricity may be converted to microwaves by klystrons, magnetrons or solid state devices, CO2 or free electron lasers (FEL), or by other means. How much power should be delivered, the land area required, the availability of positions on the geosynchronous orbit, the effects of microwaves on health, the environment, and the ionosphere, the effects on optical and radio astronomy, and possible costs have been studied intensively. According to the study there seems no doubt as to the technical feasibility of SPS. The study, Dr. Grey reported, cost approximately $19 million, of which two thirds was spent on environmental studies. The problems, he said, are both those common to large construction projects, such as public safety, and waste disposal, and those unique to SPS, such as exposure to microwaves, effect on astronomical research, effect on the upper atmosphere, effect on the health and safety of space workers. The effect of long-term exposure to microwaves is unknown. This is a new exposure for living things. Experiments on 3000 bees have shown that 30 min of exposure to microwave intensities of 3, 25, and 50 mW/cm2 have no effect on their physiology or behavior. As the peak SPS microwave intensity, at the center of the beam, is only expected to be 23 mW/cm2; no effects on the general public are expected. Further studies should, however, be undertaken. Much of the social and political concern (over and above concern about microwaves) centers around the land requirements for the receiving antenna which would cover an area something like an ellipse of 12 x 15.8 km at 23 mW/cm2, or 8 x 10 km at 54 mW/cm2 (if that much intensity can be accepted at the center of the beam) and less than 1 km across if lasers are used. International concerns center on the limited size of the geosynchronous orbit and need for international agreement on the use of this resource. In summary, Dr. Grey said that solar power satellites could provide base load power from a virtually inexhaustible fuel supply. Their development will require international agreement but there is precedent in the agreements that made INTELSAT possible. The studies completed to date indicate that effects on the environment will be less damaging than other known alternative sources of baseload power. The cost of SPS generated electricity will probably be 5-20tf/kWh delivered. Dr. Grey mentioned that he is currently paying 12(t/kWh for electricity in New York City. Asked in the question period about the energy payback referred to by Dr. Mueller in the Symposium Monday, Dr. Grey said that if fuel costs were left out, a satellite system might take 6 times as much energy to build as a conventional plant, but that if fuel is included solar power satellites show up better than fossil fuel or nuclear plants. Asked why the U.S. SPS Program is no longer being funded, he said that longterm projects are easy to cut out of budgets, that near-term problems receive first attention, and that DOE is more interested in conventional fuels, including synthetics. Fusion is receiving 100 times the support given SPS. SPS, however, has been considered by the government for only 3 years. Dr. Grey believes the hiatus in funding is only temporary, and that some people in the Department of Energy look forward to 10 years of Research and Development on Earth, 5 years of work on a small demonstration in orbit, and then operational funding at a 100-200 billion dollar level.
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