COMPARISON OF SOLAR RAY COLLECTORS TO BE USED IN THE SPACE STATION The general features of three solar ray collectors with mirror and lens systems are compared in Table 2. The preferable candidate is shown by a circle, the less likely one by a triangle and the unfavorable one by a cross. The small lens system with a single core optical fiber seems to be most preferable. This system can take the form of a panel similar to the solar cell array and, in addition, it is light in weight. The single core fiber improves the entrance efficiency. The single core optical fiber of diam up to 1.8 mm can be fabricated by present techniques and therefore the diam of lens compatible with this fiber becomes 180 mm at the concentrate ratio of 10,000. The heat concentration is also softened in this collector system because the focal points are distributed uniformly by using many small lenses. However, when the Fresnel lens is made from plastic material, the collector is damaged by ultraviolet radiation and cosmic rays. ESTIMATED TRANSMISSION EFFICIENCY The transmission efficiency estimates for the light path in various devices are summarized in Table 3. Two different transmission systems are compared here. One is the transmission system utilized silica clad bundle fiber in both the entrance and the trunk light path. A mirror or large lens collector is compatible with this system. The other is the transmission system utilized polymer clad single fiber in the entrance and polymerclad bundle fiber in the trunk light path. A small lens collector is compatible with this system. Here are shown the efficiencies of the individual parts included in the transmission path. The former system has a lower entrance efficiency because the effective entrance area of bundle fiber is lower than that of a single fiber. A rotary joint is used to transmit light through the gap between rotative parts such as gimbal point of the sun tracking mechanism. An airtight connector must be used to make the light path penetrate through the module wall. The overall transmission efficiency is largely affected by the number of connectors and joints. Table 3 shows the overall efficiency for three cases with a different number of connectors and joints. About a 50% overall efficiency can be achieved by means of present technology. INSTALLATION OF SOLAR RAY COLLECTOR IN SPACE STATION Figure 5 shows the installation of the solar ray collector on the space station. The upper side view shows the solar ray collector installed on the solar cell array structure. In this installation, the sun tracking system of solar cell array can be utilized for coarse pointing of solar ray collector and therefore only the fine pointing function is assigned to the system. Besides, this installation makes it easy to enlarge the capability by replacing the solar array with the solar ray collector. The lower side view shows the installation of the solar ray collector attached outside of the module. In this installation, the interface between the space station and the SRSS can be made clear.
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