has raised questions concerning similarities and differences in military and civilian requirements, possible needs for separate military and civilian space reactor programs and whether separate programs would lead to similar or different technologies. The requirements are still evolving as are the concepts being proposed and this leads to continued evaluation of the direction and composition of the United States space power program: a process which we think requires much more information concerning both requirements and reactor designs before rational changes can be considered. There are at least four competing nuclear technologies to choose from in the United States within the 5 to 1000 kW(e) range: 1) Out-of-Core Thermionic Reactor (OTR), 2) Thermionic Fuel Element (TFE); 3) gas cooled reactors with Brayton power conversion; and 4) SP-100. Additional concept design and development work will have to be done utilizing the first three technologies before any advantages over SP-100, the technology presently being pursued in the U.S., can be confirmed. Of the concepts listed above, the OTR, TFE, and SP-100 thermoelectric concepts offer static energy conversion systems, while gas cooled Brayton concepts and SP-100 with Stirling, Brayton, or Rankine conversion subsystems are dynamic. All of the concepts use coolant loops except STAR-C, which transfers heat from the core by conduction and radiation. Those that use coolant loops utilize a liquid metal coolant except for the gas Brayton concept. The thermionic fuel element concepts offer a conversion technique and choices of liquid metal coolants that are very different from the various SP-100 concepts. (Note: Due to financial constraints, gas-cooled reactors with Brayton conversion systems were not addressed in this study). The objective of our analyses was to compare the total masses and heat rejection radiator areas of the various power system concepts. These are the only tangibles we can compare at this juncture because the concepts are in very different stages of development, some being no more than conceptual ideas produced by a few months of study while others have been through the first design iterations. All of the power systems we considered utilize near-term technology with two exceptions: the SP-100 Rankine and the SP-100 Refractory Metal Stirling Engine concepts. The Rankine conversion technology is further out in time because it requires two-phase flow in a microgravity environment. In addition, turbines and vapor separators for use with liquid metals in the Rankine turbine concept and refractory metal components for the free piston Stirling engine must be developed and proven reliable for long term use at high temperatures. These issues are not expected to be resolved for several years. It is also important to recognize that technology risk and development costs are not the same even among systems labeled "near-term". In any comparative systems analysis it is absolutely essential to pick a common set of ground rules against which to assess the various concepts. When time and resources are limited, as in this case, these ground rules must be simplified to the point where they address only the major issues. As a result, we have performed top level system mass, area, and performance analyses based on the ground rules shown in Table 3.1. Mass estimates include all satellite subsystems except the payload. Snncp Pnwer' \Annufnrturino anri hwvlrmnwnf
RkJQdWJsaXNoZXIy MTU5NjU0Mg==