Introduction In general, the mass specific power, i.e. the electrical power output related to mass in kWe/kg is the main factor to judge the performance of a space power system [1], [2], When considering solar power systems in Low Earth Orbit (LEO), also the efficiency of the system becomes important. This is due to the fact that the collector area, either the area of solar panels or the area of a mirror system, which both are directly related to the system's efficiency, causes an aerodynamic drag in the upper atmosphere. This aerodynamic drag has to be compensated by orbit keeping maneuvers during the lifetime of the solar-powered satellite. Hence the system efficiency determines, among other parameters, the propellant mass which is necessary to keep the satellite in its orbit during its operational life. Consequently, the overall system optimization has to consider both, the mass specific power and the system efficiency. Such a study was performed at the Technical University of Munich in cooperation with the German Aerospace Research Establishment (DLR), Stuttgart, for solar dynamic systems in comparison with photovoltaic generators [3], [4], In both cases the systems were designed to power the Space Station Freedom with 25 kWe per power module. The main result of this study was that a solar dynamic system would result in drastically lower operational costs due to its three times higher system efficiency. Although NASA has been investigating solar dynamic systems for more than 25 years, such a system never has been flown up to now. In 1989 NASA was planning to use solar dynamic systems to cover the high power demands of the Space Station Freedom of up to 300 kWe. Cost estimations indicated that the use of dynamic systems would reduce the operational costs over the 30-years lifetime of the station by 3 to 4 billion US-Dollars [5], [6], In mid 1989 NASA decided not to use dynamic systems to power the baseline Space Station but to continue studying them for use as the station insolated input power (S*AcOL) solar flux eclipse time / duration orbital time / period collector efficiency efficiency of the power conversion unit efficiency of the receiver/storage unit sun-to-user efficiency
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