Figure 4-13 Power Transmission End-to-End Efficiency By evaluating the power in and power out at each point in the chain, this approach also enables an accounting of waste heat that must be dissipated by the Thermal Control subsystem or integrated coolers/radiators. Knowledge of the power level at each point in the chain, combined with specific mass data for the relevant subsystem components, enables a determination of the individual component masses used in the cost estimation process as well as in the confutation of total subsystem mass. Component cost data, embedded in the worksheet in the form of dollars per kilogram, are multiplied by the component mass estimates discussed above, and summed to produce a recurring cost estimate for the total subsystem. This estimate is subsequently modified through links to and from the Manufacturing worksheet that adjust the recurring cost downward on the basis of required production quantities for the various components. The final costs, passed to the Summary worksheet, also include a summation of estimated non-recurring costs for the Power Transmission subsystem. Providing an ability to assess SSP architectures that employ relay satellites produces a substantial increase in the complexity of the Power Transmission worksheet as well as the space segment model in general In effect, computational provisions must be established for two additional power transmission links: a space link between the power satellite and relay, and a relay to Earth link. Other complications arise from orbit geometry considerations, which affect both the time periods and elevation angles available for power delivery to specific ground sites. Many of these computational details are handled by the Orbital Geometry worksheet, which passes the required information to the Power Transmission worksheet on a site by site basis. The computations that take place in the Power Transmission worksheet, leading to a required subsystem mass and cost, involve a two-step process. In the first step, information provided by the Orbital Geometry worksheet is used as a basis for determining the size (mass, cost) of a power transmission subsystem needed to deliver a specified power level to each identified ground site. In general for the same received power level each ground site will dictate a different size subsystem. The second step of the process then automatically produces a single subsystem size that satisfies a user-selected criterion which could either be: (1) Minimum - at least one site receives the specified power level; (2) Average -
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