especially if the worst case is far away from the normal situation and occurs seldom during the operational life of the system. As an example a solar power satellite operating in a geostationary orbit can be considered. The maximum eclipse time amounts to 72 minutes. In order to fulfill the continuous power output requirement the storage capacity has to be twice as big as for the Space Station orbit. Such a storage would be oversized for 90 % of the eclipses. Furthermore, the eclipse itself represents only 4 % of one orbit, as can be seen from Figure 1. Consequently, a solar power satellite should reduce its energy production during eclipse in order to optimize the power system. This optimization process of the power system highly depends on the flexibility of the user. For manned missions a minimum power in the order of 500 We per person has to be available also during eclipse. Unmanned satellites also might require some minimum power for communication and/or attitude and orbit control (AOCS). Consequently, some energy storage is inevitable. Additionally required power depends on the flexibility of the power consuming devices and the time scheduling. For example furnaces for micro gravity experiments should be operated during sun phases exclusively, reducing the eclipse power demands. As shown in Figure 6 for the 370 km Space Station orbit the actual thermal energy delivered to the heat engine varies slightly (around 10 %) during one orbit. This
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