be required on Earth to first returns of power. The major investments for rectennas would be in the geographical regions where the power would be used. In summary, the Lunar Power System may be a reasonable scheme whereby Net New Wealth can be introduced to the people of Earth by efficiently tapping the fusion power of the sun. HI. PARAMETRIC FEATURES OF LUNAR POWER SYSTEM In a lunar power system consisting only of stations on the east and west limbs of the moon and rectennas arranged about Earth to receive all the transmitted power, the components operate on a lower duty cycle or fewer hr per year than the corresponding elements of a geosynchronous SPS. Economic viability of the restricted LPS is then dependent on realizing substantial economies per unit peak power installed compared to the SPS. While one cannot at present accurately predict comparative unit costs, we have identified most of the important factors which will govern costs of lunar industrial activities. The mature LPS with solar mirrors about the moon (or storage) and microwave reflectors about the Earth offer far higher utility than SPS. These factors and more refined engineering designs (optimization) will ultimately determine the economic viability of lunar power systems. Solar Collection A unit surface area in space continually pointed at the sun will intercept an average insolation of nearly So, the solar constant, if infrequently eclipsed. Unit horizontal area at the moon's equator will intercept an average of (1/tt)S„ during the course of a lunar month or year. Inclining the surfaces 60° toward EW to promote power leveling reduces the average direct insolation to (3/47r)5„ or 23.9% of the continually tracked value. Diffuse surface illumination from natural or artificial “white sand” can raise that value by about 30% or more. If the system is operated so that power revenue is generated whenever the element is illuminated, the installed cost of solar-DC converters per annual KW hr delivered will be lower for the LPS than SPS if the converter cost per peak watt is below 30% of the latter. Use of lunar orbit illuminators to eliminate lunar night could raise the breakeven threshold to about 60%. Greater than 100% solar illumination could be achieved by reflecting more than one solar constant down to the lunar bases via mirrors in orbit about the moon. DC-RF Beam Propagation The duty cycle of microwave conversion and beam radiating equipment will normally approach 50%. Use of lunar orbit illuminators, circumpolar rather than equatorial basing, or lunar energy storage can raise duty cycles to nearly 100%. It is a consequence of wave diffraction effects that the total radiating aperture or projected array area must be approximately 100 times larger for LPS than for SPS at a given frequency. However, for reasons discussed later, it may prove advantageous for LPS system optimization to operate at higher frequencies than for SPS. The unit costs per peak watt for DC-RF conversion will primarily involved dedicated hardware while the aperture/reflector costs will normally involve shared hardware costs with other beam sources. Overall unit costs below 50% of unit power SPS equivalents will prove competitive.
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