this mu st be viewed as a limiting capability that can only be mitigated by a constellation of relay satellites distributed in different orbital planes and positions, and possibly additional SunTowers to increase daily energy needs. Figure 4-12 is presented here to place the various results discussed in perspective. The comparative summary of power transmission opportunities is expressed as a somewhat simplified graph of average daily contact time vs. ground station latitude for different SSP orbital concepts. To summarize, an effective methodology based on the defining geometrical relationships, averaging concepts, and a quantitative database obtained by 'offline' simulations has been imbedded in the Space Segment spreadsheet model to account for the orbital geometry influence on power beaming performance for different SSP system architectures. The key characteristics of this methodology has been described in this section by use of selected examples. 43. Subsystem Detail The primary function performed by the individual subsystem worksheets, within the framework of the SSM model, is to compute an estimate of subsystem mass and cost based upon top-level requirements levied against the overall system by power delivery, orbit specification and ground site geometric considerations. However, an extremely important secondary function of the subsystem worksheets is to introduce the various options, technologies, and defining parameters available to the user through the Input worksheet. The following descriptions will briefly summarize the key features and operation of each of these subsystem worksheets. 4.3.1. Power Transmission The Power Transmission worksheet is central to most of the computations that take place within the SSM, and is by far the most detailed of all the subsystems modeled. It functions by taking user inputs related to power delivery, frequency, and essential transmitter and receiver system characteristics (device type, size, beam steering ability, etc.) to compute the mass and cost of the various components and subelements that make up the power transmission portion of the flight system Links to the Energy Storage and Thermal Control worksheets ensure that the mass and cost of these items are included as well Most importantly', links to the Orbital Geometry worksheet and the ground site locations on the Summary worksheet provide the basis for computing the varying beam coupling efficiencies and daily contact times between transmitting satellites and ground sites that allow the model to size the system from desired performance. The computational approach used by the Power Transmission worksheet is based on a Wireless Power Transmission (WPT) model developed by Richard Dickinson of JPL. At its core is a detailed end-to-end transmission efficiency chain, which starts from the point at which DC power from the Solar Collection/Conversion subsystem is provided to the Power Transmission subsystem, and extends through the point at which the received power is introduced into the terrestrial grid. The various efficiencies and power attenuation losses that make up this chain are identified in Figure 4-13. Use of the end-to-end efficiency value enables a determination of the solar input power needed to produce a desired output power at the grid, and this information is passed on to the Solar Collection/Conversion worksheet.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==