The spectral reflectance of aluminum and graphite are shown in Figures 18 and 19. The relative specularity of polished aluminum and other spacecraft materials are displayed in Figure 20. The diffuse and specular reflectivities, r^ and rs, of materials that will be used on Satellite Power System vehicles are unspecified for the most part. Consequently, for this analysis some educated judgments are needed to get reasonable estimates at this time. One item that will appear extensively is the cover glass on solar cells. For purposes of this study, the overall specular reflectance of these solar panels is assumed to be 5%, the nominal value of smooth glass. Coatings or fine scale roughening might alter this value slightly but not enough to affect the study conclusions. The corresponding diffuse reflectivity of the solar cells is more difficult to assess due to lack of data insofar as the authors are aware. Specular surfaces generally are very poor diffuse reflectors as evidenced by the curve for polished aluminum in Figure 20. On the other hand, even black velvet has a diffuse reflectivity of 1% or so. Consequently, for this study, the value of r^ for the solar panels was taken as 0.05 which is believed to be valid within a factor of two. The present Baseline calls for polished aluminum on the back of the OTV solar panels and the SPS antenna. Its specular component has a reflectivity of 80% or so depending on the finishing process and the thermal requirements. Its diffuse reflectivity is assumed to be the remaining 20% of the total Illumination. Painted surfaces can be estimated in an analogous manner. It is noteworthy that the cat-a-lac black paint and the Z-93 paint have strong specular components like polished aluminum whereas the silicon paint is quite diffuse as shown in Figures 17 and 20.
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