End of concept definition phase 1979 Completed technology verification phase 1987 Initial operational capability 1996 Total ground output of 155 GW achieved 2006 (10 percent of national generating capacity2) Total ground output of 605 GW achieved 2016 (25 percent of national generating capacity2) THE POWER TRANSFER SYSTEM Fundamental optics provides that the image cone from a mirror cannot have a smaller angular width than the cone to the (circular) source. The Sun as seen from the vicinity of the Earth has an angular width of 0. 5°. Hence an image cast from a geosynchronous orbit mirror will have a minimum width of 0. 5° as seen from the mirror. This is a width of 330 km at the Equator. Consequently the minimum area of illumination is approximately 86 000 km2. If the image strength is to be equal to a ''noon Sun" in the target area, it is necessary that the orbital mirrors have a total area in excess of the ground target area. After allowing for reflectivity losses and other inefficiencies, the smallest mirrors (for a ''one Sun" ground image) had an area of 134 000 km2 for a mid-U.S. location. Orbital mirrors of this type may have significant environmental impact. No target area could be found within the U. S. which is not currently occupied by at least 50 000 persons. The nearly constant illumination of the target area would tend to produce high temperatures, perhaps 65°C, although storms may tend to form, partially obscuring the Sun and/or mirrors. SUBSYSTEM ANALYSIS Several subsystems have broad utilization among the seven power conversion systems studied. These subsystems were consequently investigated individually for a wide range of operating parameters, permitting them to be parametrically described for optimization studies of the total systems (which are composed of several subsystems). 2. Based on a 4. 5 percent annual growth from 1976.
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