solar cells, microwave generators and receivers. We even know how to transport large payloads into space. So in that sense we understand the technology. What we do not yet have is a total systems capability which would allow us to assemble or perhaps manufacture in space this large an object. Senator Ford. How large is the technology gap between what we have and what we need? Dr. Glaser. Well, one way to gage it—as we have tried—is to estimate what kind of costs would be associated with a program development. For just the satellite, between now and, let's say, the mid-1990's, we estimate that it would cost about $20 billion to develop to commercialization. In parallel with that, we would have to develop the space transportation system and other related technology, which would cost about $24 billion. So that the total development cost would be about $44 billion. Senator Ford. The public has demonstrated a reluctance to allow new powerplants to be built in populated areas because of various environmental hazards. How dangerous is the microwave beam to people? Could I, as an individual, walk into the area of the rectenna? And would you mind having one built in your neighborhood? Dr. Glaser. As I have pointed out, the power density of the microwave beam is at such a low level that short exposure would not haim anyone, if he were to walk into the beam—that is if he could or if he wanted to. However, one would not want to live there. At the edges of the receiving antenna site the power densities associated with the microwave beam will be well below the U.S. permissible level, for continuous exposure to microwaves which is 10 milliwatts per square centimeter, and more than likely they will also meet the Russian levels, which are 1,000 times less. Senator Ford. Doctor, I believe your system does give off some waste heat at the Earth's surface, so there is some thermal pollution. How does it compare to the thermal pollution from other energy sources-—and, if I might put (b) onto that question—right now thermal pollution of the air is probably not regarded as a serious threat—is it likely to be a threat in the future? Dr. Glaser. I believe that thermal pollution indeed is one of the major problems of terrestrial power production based on the use of nuclear power including fusion power, or fossil fuels, because these plants have an overall efficiency which is less than about 40 percent. And thus 60 percent of the energy is rejected as waste heat. We have already demonstrated that we have waste heat at the receiving antenna is less than 18 percent. We believe we can reduce further, perhaps to 15 or to 10 percent. At that low level of waste heat—somewhat less than the heat released over this area of urban Washington—we can use air convection for cooling, we do not need water for cooling. Senator Ford. Do you see the satellites as a substitute for coal, nuclear fusion, or as a supplement? Dr. Glaser. At first I would see the SSPS as a supplement, because it would be built at a rate of 3, 4 or perhaps 10 SSPS per year, to
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