Fig. 14. Typical ground tracks of antenna reflection. Although the specular reflection from the antenna is not as luminous as that from the solar array, it could prove to be nearly as objectionable. Since antenna pointing constraints do not permit redirection of the beam, the alternative is to use a diffuse surface, even at the cost of some thermal performance. As has been noted above, a diffuse antenna surface adds little to the diffuse luminosity. 6. SPECULAR REFLECTION FROM CONCENTRATORS With the CR2 configuration, reflections from the concentrators will be also visible. Since uniform illumination of the solar array is desired for optimum performance, the concentrators must extend past the ends of the cell blanket to provide uniform concentration at all solar declinations with POP orientation (Figure 15). Near the equinoxes the reflection from these extensions will strike the earth at about 8 a.m. and 4 p.m. satellite time. However, some observers could see the reflection as much as 3-1/2 hours before sunrise or after sunset. The total effective area reflecting at one time reaches a maximum of 0.46 km2, or 60% of the antenna area, because the angle of incidence is about 60° when the reflection strikes the earth. The maximum luminosity would, therefore, be somewhat less than that of the specular antenna. Because the reflections are visible in daylight for the most part, they are not expected to be as troublesome. If they are found to be unacceptable, on the other hand, a simple and relatively inexpensive fix would be to stretch a sheet of concentrator material across the gap at the end of the solar cell blanket (Figure 15).
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