In this respect solar power satellites are similar to hydroelectric dams. That is, once constructed they remain available and represent real wealth which has been added to our economy. As with our previous space programs, e.g., Apollo, the development and utilization of solar power satellites would produce many technological spin-offs, enhancing our overall technological stature and thereby improving our position in the world. Solar power satellites are also a potential item for export; not only could entire satellites and ground receivers be produced and exported, but also with our satellites operational on orbit it might be possible to divert energy beams to receivers in other countries at times when our own energy demand is low (such as at local midnight below a solar power satellite station). It must be emphasized here that dollars spent on solar power satellites, or for that matter any space program, are not thrown into space. They are used by our people and remain in circulation within our country.

The energy output form of solar power satellites has direct applicability to our national needs. As indicated on the left of Figure 6, we now use far more fossil fuel for heating than we do for transportation. This heating is accomplished by combustion of coal, natural gas, and oil in our homes, industries, shopping centers, etc. This heating could be effectively accomplished by electricity. If this were done with electricity from solar power satellites, fossil fuel now burned for heating could be made available for transportation. With technological advances, such as electric cars, fossil fuel consumption for transportation could be further reduced. As a side benefit, conversion of these localized heaters to electricity eliminates numerous polution sources.

Figure 6. Solar Power Satellites Have APPLICABILITY to the Need (Produce a Usable Energy Form) Figure 7 shows how we can install as many solar power satellites as may be necessary to satisfy our forseeable energy needs. In orbit over the equator, satellites serving the United States would fall between roughly 90° and 150o of longitude. Note that in this location they are located entirely over the Pacific Ocean and not above any land mass. The arc in space in which the satellites would be placed is sufficiently long for hundreds of satellites.

Figure 7. Solar Power Satellites Can Be Installed on the Necessary SCALE Figure 8 shows again the historical cost trend for electric power in the United States and also a band of extrapolation between escalation levels of five and fifteen percent per year. It is probable that this band contains the future electrical energy trend. The predicted price for electric power from solar power satellites is also shown, along with a band to allow for uncertainties. Note that in the 1990's there is good probability that electric energy from solar power satellites may be lower in cost than energy from conventional sources. A properly maintained solar power satellite should have an almost indefinite life. After amortization of the purchase price the absence of fuel costs may allow an energy price of approximately 1ç per kilowatt hour. Thus the SPS energy price trend is downwards.

The cost of electrical energy from solar power satellites was estimated by investigating contributing factors to this cost such as the cost of ground receivers, the cost of the satellite hardware itself, the cost of transporting this equipment to space, and the cost of transmission of the electrical energy overland from the receiving point and its distribution to the ultimate users.

Ideally we should have solar power satellites today, but of course we cannot. A development phase remains ahead. Our studies have indicated however that expeditious development could lead to initial operation in the early 1990's; if solar power satellites were then placed in serial production, by the year 2000 they could be contributing nearly half of our current electric energy consumption. The use of electrical energy within the United States increased by over 6% in 1976. Shown in Figure 9 is a band of estimates of future electricity utilization. Serial construction of solar power satellites using four to six orbital construction bases could allow solar power satellites to become our primary energy source.

Preliminary investigations of solar power satellite receiver siting have indicated that these receivers can be placed relatively near their demand points, as shown in Figure 10. Hence, solar power satellites are not a regional energy solution, such as ground solar power which clearly best performs in the southwest, or ocean thermal energy conversion which is probably best off the southeastern United States. The 200 antennas shown here would be adequate for an output of approximately one million megawatts or about twice the current U.S. generating capacity.

(POWER SATELLITES ARE NOT A REGIONAL SOLUTION)

. - RECEIVING ANTENNA

(200 SHOWN 1,000,000 MW CAPACITY:

TWICE CURRENT U.S. CAPACITY)

Figure 10. Solar Power Satellites Deliver Energy to the Right LOCATIONS

Table 4 discusses environmental factors relative to solar power satellites. SPS studies have indicated that solar power satellites may have the lowest environmental impact of any potential new energy solution. The land area requirements for the ground receivers appear large; however, the land area required for a SPS is smaller than that required to strip mine the coal to produce the electrical energy which such a satellite can produce in only 20 years of operation.

Table 4. Solar Power Satellites Will Have MINIMAL ENVIRONMENTAL IMPACT

· RADIATES WASTE HEAT OF POWER GENERATION TO SPACE, NOT TO THE ENVIRONMENT.

⚫LAND AREA REQUIREMENTS ARE COMPARABLE TO OTHER SYSTEMS; EARTH RECEIVERS
ARE ANTENNAS POSITIONED ABOVE THE GROUND.

THE MICROWAVE BEAM WILL BE SAFE. AT THE PERIMETER OF THE EARTH RECEIVING AREA,
MICROWAVE ENERGY WILL BE 1/100TH OF U.S. STANDARD.

CONTRIBUTION TO AIR POLLUTION IS ROCKET EXHAUST, WHICH IS PRIMARILY WATER,
DURING LAUNCH.

Criticisms of the solar power satellite concept have centered on the microwave beam which would be used to transmit energy from space to the ground. However, it appears this beam can be made completely safe.

Figure 11 illustrates a cross section of such a beam which carries 5.9 million kilowatts. At the center of the beam the strength is approximately 23 milliwatts per square centimeter, about one quarter of the strength of desert sunshine. Approximately half way from the center of the ground receiver to its edge the beam strength has fallen to 10 milliwatts per square centimeter (the current U.S. microwave exposure standard). Nearer the edge the signal strength has fallen to 5 milliwatts per square centimeter, the current standard for microwave oven leakage. At the edge of the receiving array, where it is no longer economically practical to install receiving antennas, the signal level is at 1 milliwatt per square centimeter or 1/10 of the U.S. continuous exposure standard. A fence to exclude the general public is shown 8/10 of a mile from the receiver edge. At this fence, the signal level of the beam from space will be 1/10 of a milliwatt per square centimeter or 1/100 of the U.S. microwave exposure standard. There will be some additional peaking, or concentrations, of microwave energy in rings surrounding the ground receiver. However, these peaks are quite weak and never exceed the level at the fence. Consequently, people in these regions would not be exposed to high microwave levels and would in fact probably encounter higher microwave levels from other electronic devices which they use in their normal day to day activities. Aircraft would probably be routed around these microwave beams.

The seven factors described above thus contribute to the overall suitability of solar power satellites as a national energy solution.