the power delivered to all the sites averages to the specified power level; or (3) Maximum - no site receives less than the specified power level After a single subsystem size is determined, the process completes another pass through all the ground sites and computes the power delivered to each. This information, along with other site related data, is passed to the Summary worksheet where it is reported in the Ground Sites table. The mass and cost of the power transmission subsystem, sized by selection from the above criteria, is reported on the Summary worksheet as well If relays are included in the architecture, the mass and cost of the power transmission subsystem for the relay satellite is computed concurrently with that of the power satellite and also reported on the Summary worksheet. 43.2. Energy Storage Space-based energy storage has been included as part of the space segment modeling and that subsystem has been assigned a separate worksheet within the SSM. However, for purposes of requirements and sizing, the energy storage function is modeled as an integral part of the computations that take place in the Power Transmission worksheet. There, if energy storage is desired, its storage capacity requirements are computed from the input power required by the power transmission subsystem and contact times for power delivery to the ground sites. The mass and cost of any energy storage is included in the totals for the power transmission subsystem The Energy Storage worksheet acts primarily as a lookup table of mass, cost and efficiency data associated with various energy storage technologies. The table presently includes data for advanced battery, fuel cell, flywheel, and Superconducting Magnetic Energy Storage (SMES) systems. Based on user input, which provides a selection from among these choices, (“None” is also an option), the lookup table delivers the corresponding scaling factors for mass (W-hrs/kg) and cost ($ZkW-hr) along with energy storage efficiency to the power transmission worksheet for inclusion in the confutations discussed above. 433. Solar Conversion The worksheet covering the Solar Collection/Conversion subsystem is self-contained and employs an end-to-end efficiency approach similar to, but far less detailed than that used by the Power Transmission worksheet. The worksheet also contains a technology parameter database, such as used by the Energy Storage worksheet. Figure 4-14 illustrates the major elements of the worksheet with an example computation for a SunTower power satellite that uses advanced photovoltaic technology and Fresnel reflectors with an assumed concentration ratio of 5. The elements of the power efficiency chain, as well as some of the efficiency and tolerance values used, are taken directly from the 1978 SPS Reference design. Other values, reflecting the projected performance, cost, and efficiencies of various conversion technologies, are obtained from the lookup table at the top of the worksheet, keyed to the technology selected by the user on the Input worksheet. The values contained in this table were a product of the Phase H Technical Interchange Meeting at NASA/LeRC. Bolded values represent opportunities for direct user inputs into this worksheet. The worksheet uses the required output power, confuted by the Power Transmission worksheet, divided by the end-to-end efficiency to derive a required solar input power. The known value of solar flux at 1 AU can then be used to determine the required solar collection area, and in the case of the SunTower concept, the number of reflector pairs required. Note that because the performance metric for photovoltaics is often provided in terms of W/m2 as well as W/kg, subsystem mass values are computed
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