4.0 CONCLUSIONS AND RECOMMENDATIONS 4.1 CONCLUSIONS The ground illumination from sunlight reflections off the Space Power System spacecraft have been evaluated for the Baseline Design. A variety of configurations, orientations, and operational conditions were considered in this analysis. Because of the expectation that these vehicles will be viewed by many ground observers, those conditions that are thought to produce the brightest ground irradiance have been selected for evaluation. For the most part, only normal operations with controlled orientations have been assumed; however, a couple out of control abnormal orientations are also treated. A summary of ground irradiance levels that have been calculated is presented in Table 5. The large size of the Space Power System elements causes even diffuse reflections to appear as very bright light sources. The present Baseline vehicles are held together by beams that are painted with highly reflective material. However, the dominant surfaces for reflected light are the solar panels of the OTV and SPS. These areas consist of highly specular, low reflectivity cover glass over dark absorbing cells on the front side and shiny aluminized plastic dielectric on the back (see Tables 2 and 3). Consequently, most of the reflected light is very directional; diffuse reflections are proportionately much dimmer due to a lack of large diffuse surfaces. The diffuse cases summarized in Table 5 are all relatively bright in comparison with stellar sources. For example, the SPS in GEO is comparable to the stellar magnitude of Venus at its brightest. The OTV/SB combination in LEO is visible during daylight hours but, of course, is at too low an altitude to be illuminated at night. The specular cases cited in Table 5 produce much brighter ground illumination. However, this irradiance is restricted to small, fast moving spots. The actual duration of these "glints" of specular reflections varies from about one second for the OTV/SB in LEO to two minutes for the SPS antenna. An important consideration is the sudden onset of the specular irradiance compared c to the much dimmer diffuse irradiance. Enhancements of 10 are common. An
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