range has been the baseline for solar power satellite power transmission since the beginnings of studies of this energy option. Progress in laser technology has been rapid in the past several years. Recently a number of papers and articles have appeared either advocating or analyzing the potentials of laser power transmission for solar power satellites. In principle the laser option simply represents a frequency change by a factor of 104 to 105. However, this means that different types of devices will presumably have to be used to convert sunlight (or electricity produced from sunlight) into electromagnetic energy, form the energy into a controlled beam and reconvert the energy on the ground to electric power for industrial or commercial use. In addition this frequency change means that very much smaller transmitter and receiver apertures can be used with high aperture-to-aperture efficiency. Therefore much smaller individual power transmission links might be economically attractive. Many of the papers published regarding laser transmission have employed assumptions or analyses that make comparison with reference systems quite difficult. In some cases these assumptions appear to have been based on superficial subsystems analyses; in other cases, they simply represent either more optimistic or less optimistic extrapolation of technology. Two examples may be drawn from the studies of optically pumped lasers by Rather (1) and Taussig (2). Rather’s paper considered optically selective filters allowing the solar concentrator to concentrate only a relatively narrow band of the solar spectrum on his iodine laser. The portion of the spectrum he selected immediately surrounds the pumping wavelength for the iodine laser; this allows achievement of a comparatively respectable laser efficiency (21%). Rather’s estimate of concentrator mass unit per area, however, is more than an order of magnitude less than those derived by recent solar power satellite systems definition studies (3) which analyzed concentrator requirements and design characteristics in some detail. On the other hand, Taussig’s analysis estimates concentrator masses to be roughly twice those derived by the SPS systems studies, but he employs extremely optimistic thermal radiator masses. The data developed by the system studies allow construction of very simple parametric models for the first-order comparative evaluation of new options using parametric representations of subsystems such as solar arrays, structures, power distribution, thermal radiators and thermal dynamic power cycles. This data base permits a relatively quick normalization of the existing laser transmission results to the systems study results to allow a valid first order comparison of the relative merits of power transmission by laser or micro wave. In this paper we compare two types of microwave power transmission satellites (the silicon photovoltaic and potassium Rankine systems) with five laser options representative of those described in the literature. These are: (1) a CO2 electric discharge laser powered by a solar array; (2) a CO gas dynamic laser powered by a Brayton cycle; (3) a free electron laser (FEL) powered by a solar array; (4) a direct solar optically pumped laser (OPL) modelled after the Rather concept (employing a selective concentrator); and (5) an indirectly optically pumped CO2 laser (IOPL) after Taussig. Table 1 presents cost and mass estimating factors, while Table 2 summarizes the simplified quantified block diagrams for these systems. Note that in the block diagram schematic the electric discharge laser and the free electron laser appear simply as alternative power transmission means. Because of their lower efficiency these two options require rather more substantial thermal control than does the microwave power transmitter although the latter also has a quite significant thermal control requirement. The gas dynamic laser system is vaguely comparable to the thermal engine SPS with the generator, power distribution,
RkJQdWJsaXNoZXIy MTU5NjU0Mg==