2.0 STATEMENT OF PROBLEM 2.1 BACKGROUND Limited terrestrial energy sources have led to investigation of Space Power Systems that would collect solar energy and beam it via microwaves to power stations on the ground. The Reference System consists of a Staging Base in LEO, a fleet of Orbit Transfer Vehicles for movement of supplies from LEO to GEO and assembly and operation of Solar Power Satellites in GEO. All of the structures would be very large in comparison with today's satellite sizes, and include large plane surfaces to collect solar energy. As many as 60 SPSs are presently contemplated for deployment early, in the next century, which would require a substantial entourage of assembly and service vehicles. Due to the enormous size of these spacecraft and their assembly vehicles, they may be viewed routinely by large numbers of ground observers. The brightness of sunlight reflections off various components changes markedly as the vehicles rotate along their trajectories. Many surfaces will undoubtedly be coated with optically diffusing material, but the present baseline configurations also include large flat areas that are specular such as glass, polished metal, and smooth composites. Owing to the large size, relatively low altitude (at LEO), and/or specularity, some reflections will be exceptionally bright. A typical reflection configuration for SPS at GEO is illustrated schematically in Figure 1. The level of ground illumination is needed to evaluate potential effects, if any, such as radiant energy in observer's eyes, skybrightness for optical astronomy, and changes in animal behavior. For example, there is reason to investigate how well the human eye can adapt to this unusual light source. The reflections will appear to ground observers as very bright starlike points of light in relatively dark night sky. Since contraction of the iris is controlled by overall illumination levels, the eye pupil may accept more light energy than desirable from these point sources, and produce abnormally high retinal irradiance. Since the eye relies only on the iris and blink reflex to control total irradiance, it is important that the power density of such point-source retinal images does not exceed safe limits.
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