SUNLIGHT REFLECTIONS FROM A SOLAR POWER SATELLITE OR SOLARES MIRRORS SHOULD NOT HARM THE EYES Dr. Michael T. Hyson Bioinformation Systems - California Institute of Technology Pasadena, California 91125 A Solar Power Satellite (SPS) located at geosynchronous orbit (GEO) could collect sunlight above the atmosphere and return 5-10 gigawatts of electrical energy to the earth using a microwave beam from an array of klystrons arranged as a transmitter one kilometer in diameter. The transmitter must point continuously at a receiver on the earth. During some phases of the SPS orbit, the transmitter would reflect an image of the sun to the ground. It has been suggested that the reflected beam could harm an observer's eyes. It is shown here that this problem is minimal. The reflection, while bright, would not be dangerous. In the worst case, where the transmitter is assumed to be a perfect mirror reflecting the sun's image normal to the atmosphere, the total energy received by the eye would be 3.36 x 10“7 watts. The eye's optics would blur the 5.6 sec of arc image of the transmitter over a disk approximately 6 minutes arc in diameter, reducing the maximum intensity at the retina by 99%. A given cone in the retina would receive even less energy due to the constant random microtremors and microsaccadic movements of the eye muscles which move the retina over an area some 8 minutes of arc in radius, even during steady fixation. Therefore, very conservative estimates made here show that the reflections from the transmitter could be viewed safely for at least 3.2 hours and that the entire SPS structure could be viewed for a minimum of 1 hour. The Solares mirror is briefly considered and is shown to be safe to view for at least 2.4 minutes. Keywords: Power generation, alternate energy sources, solar power satellite, solares mirrors, solar energy, extraterrestrial resources, space industrialization, SPS environmental impacts, eye movements, visual perception. An SPS at geosynchronous orbit (Figure 1) will sometimes reflect sunlight to the ground. Solares mirrors may be used to provide increased solar insolation. It was found that the reflected light from these structures would not be at dangerous levels. The subtense of an SPS transmitter array would be 5.74 sec. arc (Figure 2). Worst cases were assumed; the SPS was treated as having albedo = 1, at GEO altitude, at the zenith, reflecting light into an 8 mm pupil of a dark adapted eye (Figure 3). The illuminace at the eye is a function of the sun's intensity, the atmosphere's transmittance and the ratio of angular area of the structure and sun, i.e.:
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