Option 3 offers potential advantages since the radiator can be an integral part of the facet structure. However, there are two major problems. The first is the NAK mass between the radiator and the turbomachine. The NAK alone can weigh more than 136 000 kg, depending on the allowed flow losses. This mass is greater than the radiator mass for option 1. Secondly, the facet surface is not continuous, having NAK line connections between the facets. This study has not revealed any mass advantage for option 3. Based on the study to date, option 1 is the best choice. The radiator will consist of two panels that are 180 m long and approximately 60 m high. A summary of the mass assessment for the three options is presented in Figure 7-35. These conclusions are based on an inlet temperature of 245°C, an outlet temperature of 110°C, and tube-fin type construction. The SPS concept configuration does not complement the radiator size, since the radiators have to be structured relatively close to the main structure. With the exception of option 3, the view factor can never be greater than 0. 5. Nevertheless, minimum combined radiator/support structure mass is represented by a combination of options 1 and 2. The radiator size is very sensitive to its inlet and outlet temperatures. Some consideration has to be given to the effect of turbo machinery efficiency on radiator temperature. The sensitivity of radiator size to the inlet temperature is illustrated in Figure 7-36. If the inlet temperature is too low, the entire system suffers a severe mass penalty. Since total SPS cost is most sensitive to mass, tradeoffs are necessary between turbomachinery performance and total system mass. For this study a design point, as indicated, was selected. Optimization of the radiator mass and area on a cost basis has not been completed. 7. 2. 4 POWER DISTRIBUTION AND CONTROL SUBSYSTEM Based on a preliminary analysis, an operating voltage of 20 kV de was selected for the thermionic-Brayton system. Low voltage de power from the thermionic diodes is converted to 20 kV by a motor-generator set or an equivalent static converter. The output of the thermal engine is converted to 20 kV de with rotating generators. Thermionic-Brayton modules producing 32. 25 MW are connected through circuit breakers in groups of 40 to 16 main power lines. Thin wall aluminum tubes are used for all power conductors.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==