an indication of the most attractive values of PG. In case larger powers than the nominal purchase cost or power limited links are desired, the desired patterns will change and become somewhat squarer, like the Rockwell “Bessel-J” patterns (6), with appropriate different link constants. For these concepts equation (5) suggests that a useful concept may be the aperture utilization efficiency: Both 7]v and G* are only useful figures of comparison at equivalent beam efficiencies and receiver edge intensity cutoffs. Secondly, solar thermal cycle power satellites have not been explicitly considered. To first approximation the entire thermal cycle can be treated as a mass per unit power, especially if the satellites are made of many small power modules. Space does not permit further discussion here, but it should be noted that thermal cycle power systems have always been fertile ground for parametrics. Lastly, power distribution mass has not been explicitly treated in terms of a cost and/or mass penalty. This can be done as a separate analysis but, again, space does not permit it here. It is a good idea to keep analytical parameterizations to no more than about half a dozen variables in order to avoid confusion. For this reason computer programs like Boeing Integrated Sensitivity and Interrelationships Analysis (ISAIAH) program are used when more complex analyses are required. ISAIAH in particular can handle up to 95 independent variables and can provide hard copy graphic outputs. 4. SUMMARY The basic methodology of system-level comparison of various solar power satellite design options has been shown. The results indicate that the most attractive laser power transmission solar power satellites are the free electron laser option and the optically pumped options. The laser power transmission power satellite does appear to be more massive and costly than the microwave power transmission power satellite. However, this may change once laser power transmission is given technically aggressive, “let’s make it work” oriented study comparable in depth to microwave power transmission. In addition, some simple system power sizing relationships for photovoltaic power satellites have been developed and explained. They lead to system powers in the megawatt range for laser power transmission systems and powers in the gigawatt range for microwave power transmission systems, and may be extended to other types of solar power satellite. Acknowledgment — The editor wishes to thank Dr. E.F. Schmidt and Dr. Arthur Kantrowitz for their assistance in reviewing this paper. REFERENCES 1. J.D.G. Rather, New Candidate Lasers for Power Beaming and Discussion of Their Applications, Astronaut. Aeronaut., 61, 313-332, Jan. 1978.
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