or power transistors) offer good switching speeds and could be made with little non-lunar material, but may be difficult to manufacture in space, will require radiators, and create small losses (about 99% efficient). Little information about vapor-phase switchgear was available to the study team, but the fact that it was selected in earlier SPS studies suggests that its lifetime and efficiency are high and its mass is low. Experience with lunar material substitutions in other subsystems suggests that at least 90% of the mass in a vapor-phase switch could be replaced with lunar material, e.g. aluminum conductors and glass envelopes. However, a vapor-phase switch design has not been examined to verify this assumption. Because of its acceptance in earlier designs and the belief that it can be built with little non-lunar material, vapor-phase switchgear was selected. However, further study is needed to select an optimum switchgear system. 4.3 VOLTAGE CONVERSION Previous studies (1,2,3) have used an oscillator-transformer-rectifier system for DC to DC conversion at the microwave antenna. The major mass components of this system are the transformer, the inductors, and the capacitors. The transformer requires active cooling. The only non-lunar material required in any of the major items is pumps and coolant for the transformer. Non-lunar material would also be needed for the oscillator and the rectifier. Transformers are only about 98% efficient, making the overall conversion process about 96% efficient. Modern power electronics provide DC-DC conversion at over 98% efficiency without using transformers.(4) This increased efficiency reduces non-lunar mass needed for cooling and reduces the mass of the power conversion system. The semiconductor voltage converters were assumed for this study. 4.4 ENERGY STORAGE Stored energy is required during eclipses to maintain essential systems and to keep RF amplifier cathode heaters hot. For a 5 GW SPS, the required energy storage is 6 MW-hrs.(2, vol. 4, p. 159) Storage alternatives considered in this study are compared in Table 4-1. TABLE 4-1 ENERGY STORAGE TECHNOLOGIES AND MASSES FOR 5 GW SPS
RkJQdWJsaXNoZXIy MTU5NjU0Mg==