rejection penalties may need to be assessed. (6) These results should not be taken as a condemnation of a laser power transmission. Rather, they should be considered as indicative of areas where further research and study is needed. Even at these masses and costs, lasers might be attractive as an adjunct to microwave transmission to serve low power links. (7) Little motivation was seen for high (i.e. dangerous) laser beam intensities. The value used was 1000 watts/m2, i.e., one sun, about 4 times the microwave link density. At this intensity, the receiver cost was seen as a relatively minor item in the laser systems. (8) All of the laser power satellites are very sensitive to the laser efficiency because it strongly influences the masses of both solar energy capture subsystems (i.e., solar concentrators or solar cell array) and thermal radiators. Massive subsystems provide dual penalties in that one not only has to pay for the subsystem but its transportation and construction as well. It may be seen that the laser systems are in general heavier than the microwave systems and from somewhat to much more expensive. The best laser option appears to be the photovoltaic free electron laser system. Surprisingly, to us, the optically pumped systems do not show the cost or mass advantage that one intuitively expects them to have because they have no solar/electric conversion step in the power conversion chain. This appears to be largely due to their lower solar/laser conversion efficiency which necessitates substantial complexity in solar concentration and heat rejection hardware. Of the laser systems, the three that we feel are most worthy of further pursuit are the photovoltaic free electron laser system and the two optically pumped systems. The reason for this is that these are the systems that are most likely to be able to achieve higher conversion efficiencies. In the case of the free electron laser, one might expect to eventually achieve DC/light efficiencies as high as that achievable from klystrons (i.e., .8) so in fact the system would be much like a “conventional” solar power satellite. For selectively concentrating optically pumped systems, the main invokable technologies are lightweight solar optics and separate lasers to utilize varying wavelengths of the solar spectrum effectively. Both of these improvements also apply to the concentrating cavity optically pumped laser system which, due to the inevitable (1 +r))/r) radiator mass dependence, will be in the same cost range as the other laser systems if efficiency r, = .2 instead of. 15. Finally, a somewhat higher radiator temperature may greatly decrease the concentrating cavity option’s radiator mass. 3. POWER SATELLITE SYSTEM SIZING Some commonly used figures of merit for a power satellite system are satellite mass, system cost and system cost per unit installed grid capacity. The variations of these figures of merit as a function of assorted parameters (such as downlink power, frequency, solar cell efficiency or microwave transmitting array area) yield information as to which approaches should be taken in optimizing the system design and in developing new technology. It is a good rule of thumb that the simplest approaches yield the best results. When they don’t, it is the designer’s job to know why. Feedback should be introduced into this procedure by calculating system parameters and checking them against the “reality” of existing power satellite system point designs, such as the DOE/NASA Reference System Design (4), the Boeing Preferred
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