these cycles. A recuperator was used in the high temperature steam cycle. Coolers are not needed in any of the cycles because the cycle working fluid can be utilized as the radiator fluid. 2.5.4 Rankine Cycle Technical Discussion The Rankine cycle SPS design (1) has the same general configuration as the Brayton cycle SPS. The input power necessary for the Rankine cycle engines depends on the efficiency of each cycle. The mass of each major component of the Rankine cycle after substitution of lunar materials is given below. The suggested lunar materials for use in these components are also listed below. These materials were chosen based on the available information about the temperature, stress, and conduction requirements. 2.5.4.1 Radiator The radiators for the steam cycles are much more massive than those of the potassium cycles. This is due to the low rejection temperatures selected for the steam cycles to achieve good efficiencies. The heat pipe radiator for the Rankine cycles uses the working fluid of the cycle as coolant, eliminating the need for a heat exchanger in the cycle. The radiating sheets were assumed to be aluminum. Stainless steel was used for the heat pipe shells and the wicks. Water was used as the heat pipe working fluid.
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