APPARENT LUMINOSITY OF SOLAR POWER SATELLITES L. E. LIVINGSTON Lyndon B. Johnson Space Center Houston, Texas 77058 Abstract — The objective of this investigation was a quantitative characterization of solar power satellite luminosity as seen from the earth. The reflective characteristics of the reference photovoltaic satellite configurations are defined. Diffuse reflection from a single satellite will, at maximum, fall between magnitudes -4 and -5. A 60-satellite fleet will have a maximum total luminosity equivalent to a single object of magnitude -9. Specular reflections from the array and antenna will be of magnitude -12 to -15, but visible only occasionally for about 2 minutes at a given location. Methods of preventing specular reflections from striking the earth are presented. Thermal cycle power conversion systems are discussed qualitatively as a means of reducing diffuse luminosity. 1. INTRODUCTION Several large artificial satellites, such as Echo, have been easily visible to the naked eye. Since the proposed Solar Power Satellites (SPS) will be much larger than any satellite launched to date, they can be expected to appear much brighter than previous satellites. The objective of this paper is a quantitative characterization of SPS luminosity. Because optical astronomy will be directly affected, luminosity is expressed herein in terms of conventional astronomical magnitudes as seen from the ground. The two current reference configurations (1) are illustrated in Figure 1. The gallium arsenide configuration has a concentration ratio (CR) of two to reduce solar cell area; the silicon configuration is unconcentrated (CR1). In both cases, the satellite is in geostationary orbit, the solar array is oriented toward the sun with the long axis perpendicular to the orbit plane (POP) at all times, and the transmitting antenna is continuously pointed toward the rectenna on the ground. 2. REFLECTIVE CHARACTERISTICS For optimum thermal properties, the surface of the antenna is presently envisioned as a specular surface with a reflectance as high as 0.98. The radiating slots account for about one percent of the gross antenna area, and gaps between subarrays and other irregularities might be two percent, giving an effective reflectance of perhaps 0.95. Efficient microwave performance requires that the subarrays be parallel
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