A mass statement (preliminary estimate) for the RPBR system is given in Table 5-7. Table 5-7. Rotating Particle Bed Reactor SPS Mass Statement Space Flight), "The laws of optics provide that the reflected image of the sun, seen from a facet of the mirror, must appear at least as large as the sun itself, seen from the mirror." As a consequence, the smallest image which can be produced on Earth by any geosynchronous orbit mirror is approximately 330 km (205 s.m.) in diameter. Figure 5-32 shows that an orbital mirror can not provide full illumination at all times; for example, at noon the mirror is edge-on to the sun and no image can be produced. Fig. 5-32. Mirror Attitude Changes Around Orbit Figure 5-33 shows the approximate combined output of the sun and the satellite mirror assuming a mirror sized to produce at midnight an output equal to the sun at noon. The average of the combined output over the 24 hour period is almost exactly one "sun." Fig. 5-33. Combined Mirror and Solar Output The target size to be shown is based on the following somewhat optimistic assumptions: 1. Optimum mirror curvature, i.e., all elements of mirror surface "aimed" at target center. 5.10 SOLAR POWER TRANSFER (CONCEPT 9) A mirror system in geosynchronous orbit which would directly reflect sunlight to an area on the surface of the earth might be used to enhance the performance of a ground based solar power generating system. Analysis was first concentrated on the size of image which a geosynchronous mirror could produce: An important optical effect must be considered. Since the sun is not a point source, its angular width of 0.53°, as viewed from the region of the Earth, will be duplicated by the reflected light cone produced by any mirror, no matter its size (see Figure 5-31). Fig. 5-31. Cone Angle of Solar Image is Equal to the Cone Angle to the Sun This was noted in 1929 by Herman Oberth on page 354 of his "Wege Zur Raumschiffahrt" (Ways to
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