In LEO there is a problem due to atmospheric drag which reduces the satellite altitude. This requires regular orbit compensation manoeuvres which increases the overall mass of the system. Since Solar dynamics systems are inherently more efficient than photovoltaics systems, less area is exposed (even after allowing for the large radiators required to reject the waste heat) requiring less orbit correction to be provided. Other Factors Pointing Solar dynamic systems have a pointing requirement of 0.1° in order to obtain the high concentrator ratios necessary. This is a lot higher than photo-voltaic array type systems which can handle de-pointing typically of 1-2° with little impact on the power output. Figure 7.12 Cost Comparison for Space Station Freedom Power Generation [Fordyce,1992] Heat Rejection In the process of generating heat energy, a SDS produces waste heat which must be rejected using some kind of radiating surface. For large systems, a heat transport system using pumped liquid or two-phase fluid loop is necessary to transport heat to the large radiator that is required. For a photovoltaic system no waste heat is produced and therefore no radiator is required making it a simpler system. 7.1.4 New Technologies This section will cover power collection technologies different from the technologies having to do with the photovoltaic and solar dynamic conversion systems. Thermoelectric and thermophotovoltaic theory will be explained. We will also describe a new type of solar dynamic generator. Special attention will be given for describing the actual state of these technologies and their effect on the implementation of any large scale SPS. Additional subsystems involving promising technologies will be investigated. For example such a system is the liquid droplet radiator.
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