It is noteworthy that, at most, the enhancement would be only threefold in LEO and 15-fold in GEO beyond normal controlled operations. Some perspective on the relative importance of these irradiance levels can be derived by a comparison with the solar irradiance. In- solation is about 1400 W/m , substantially greater than any of the reflections. However, the sun is an extended source subtending 32 arc minutes; whereas, the OTV in LEO subtends 11 arc minutes (500 km altitude) at the most, and well beyond LEO both OTV and SPS subtend less than one arc minute, the resolution of the eye. Thus, the power density in this direct solar image would be as much as 10-fold less than that for the OTV in LEO, and 1000-fold less than the OTV and SPS in GEO. Apparent stellar magnitude provides another useful basis for comparison. Using the sun as the standard, the formula for the visual magnitude of a light source is given by where H is the ground irradiance. Thus, for example, diffuse reflection from SPS in GEO (D2) would have an apparent magnitude of -3.6, and specular reflection from the SPS antenna in GEO (S3) would have a magnitude of -13.8, comparable to the full moon. The methodology for calculating sky brightness created by a diffuse source is also presented. This calculation requires elaborate tabular entries. The sky irradiance for a typical set of observation directions, displaced a reasonable angular distance away from the source, is on the order of 1% of the direct irradiance from the source. The sky brightness for other observation conditions would be evaluated on a case-by-case basis using the tables in the report. These worst case irradiances might be reduced significantly and perhaps eliminated by appropriate modifications to the design and/or operation of the spacecraft. By slight changes in the vehicle orientation, the specular reflections from the large solar panels could be directed away from the earth. Another modification might be to introduce surface curvature or misalignment of flat panels that would diverge the specular beams. Finally, the specular surface quality of other structures might be eliminated (or sharply reduced) by etching or coating the materials to create a diffuse reflection.
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