multiplied by the factor pAHirR2, where p is the diffuse reflectance, A is the area of the reflector and R is the distance from the satellite to the observer (3). Using subscripts c, k, s and a for the solar cells, Kapton substrate, structure and antenna respectively, we have Because of the significant contribution of the Kapton substrate, the difference is less than a magnitude. If the cells were the only reflective component, the change of reflectance from 0.125 to 0.04 would result in a change of 1.26 magnitudes. Variation in other parameters has less effect. A reduction in substrate reflectance from 0.67 to 0.2 increases wmax (algebraically) by 0.1 to 0.3 magnitude, depending on the solar cell reflectance used. Eliminating structural reflectance completely gains at most 0.1 magnitude. If, on the other hand, the antenna were diffuse rather than specular, the magnitude would be decreased by 0.1 to 0.3. Thus, the maximum plausible luminosity of the SPS, including a diffuse antenna surface, is It should, of course, be kept in mind that the areas and reflectances quoted here are estimates and subject to change as the SPS evolves. However, a major variation in parameters is necessary to effect a significant change in luminosity. All luminosities quoted above assume the sun at the equinox and the observer at the equator. At the solstices, the illumination on the array is reduced by 8%, resulting in an algebraic increase of 0.09 in the apparent magnitude. For an observer not on the equator, the increased angle between the line of sight and the normal to the surface increases the apparent magnitude by a maximum of 0.013. The solar array is always oriented toward the sun. Thus, the illuminated face of the CRl configuration is visible from the earth from about 6 p.m. to 6 a.m., local apparent time at the longitude of the rectenna, with maximum luminosity at midnight. At other longitudes, the times will vary as much as half an hour due to the At 40° latitude, an observer is about 37,500 km from a satellite at the same longitude. Using this value for/? and taking the maximum diffuse reflectances given above, we obtain
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