grows [7], The main reasons were higher risks and higher development costs involved in the use of the dynamic option. Table 1 summarizes the latest data available to compare the two solar power systems envisaged for the Space Station at that time. Current planning of a joint Russian-US Space Station based on the Mir 2 design again includes the solar dynamic option [8], This paper discusses certain aspects of solar dynamic power systems, not solely with regard to LEO application. It focuses on the influence of the orbit parameters on mass and efficiency of such a dynamic system. Assumptions and Requirements The following investigation will concentrate on circular orbits, because they are most relevant for Space Stations and other high power converting satellites. Furthermore the earth is considered as being a sphere with a homogenous 1/r2 gravitational field. Another assumption is that the main part of the aerodynamic drag is caused by the area of the solar collector. The area of the radiator of a solar dynamic system is neglected. This is a realistic approach, because the radiator is either in the aerodynamic shadow of the collector or it can be turned in a position parallel to the orbital velocity vector without decreasing its performance. Especially for a manned Space Station it is important to satisfy power demands during the whole orbit, independently whether the solar collector is in the sunlight or in the earth's shadow. Therefore, a solar power system for orbit application usually is equipped with a storage subsystem which is charged dining the sunlit portion of the orbit and delivers energy during eclipse. The Space Station photovoltaic option relies on batteries, whereas the solar dynamic system stores heat in a latent heat storage. The heat storage allows a continuous - instead of a stop-and-go - operation of the heat engine. This is necessary to achieve an appropriate operational life in the order of ten years. In a first approach it is assumed that a continuous power supply is required. As a typical size a 25 kWe power module is considered. In order to satisfy the continuous power demands the system, especially the storage capacity, has to be designed according to the orbit with the lowest insolation, i.e. the lowest energy input (worst case). The lowest energy input to the receiver results: • when the Earth to Sun distance is maximum, i.e. the solar flux is minimum (1326.3 W/m2) and • when the shade period reaches its maximum (maximum eclipse) and • at the expected end-of-life (EOL) performance of the collector. These minima determine the size of the solar collector and the storage subsystem.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==