for coordinated mutually beneficial research. A programmatic study, funded by the German Ministry for Research & Technology and performed by Dornier, DLR and others, will contribute to these topics, being a contribution to attain a competitive place in the commercial business of future space utilization and decentralized terrestrial energy supply. As long as there is no feasible technology available for non-material bounded energy transmission from higher to lower orbit levels—and down to earth—energy provision and consumption will be part of a stand-alone system and thus underlying the same design and operational requirements, mainly of LEOs. The provision of an increasing future power demand has to leave the lines of the realization of sequent missions, and rather enter a modular or blockbuilding based supply system. Since the size of exploitation of solar energy in space and on earth is proportional to the size of the collector area there is a strong tendency for series production similar to photovoltaic. It is obvious that it is stringent to decrease development and maintenance costs for the variable power demands of future unmanned, man-tended, manned and space processing missions. The rated power of solar thermal systems for space application corresponds to the lower end of a scale comprising stand-alone and multimegawatt grid connected terrestrial units. But high temperature materials, control strategies and quality assurance problems will profit from a joint consideration. It has been found that the evaluation of electricity cost, COE (cents/kWh), a common procedure in terrestrial energy economics, provides also a suitable tool for the assessment of design variations for space power supply. Comparing, e.g. the basic solar energy conversion systems, photovoltaic and solar-thermal, it is easily seen that thermal energy storage smoothing power supply decreases the COE of solar-dynamic systems whereas a battery storage for the same purpose increases the COE of photovoltaic systems. Furthermore terrestrial reliability, demonstrated by a pre-series production lot, is considered to be at least equivalent to a time-compressed laboratory check of a single unit under doubtfully simulated test conditions. The paper will present these aspects of a proposed coordinated development strategy in more detail, pointing out also that the economic benefit will probably be larger than in case of the commercialization of any spin-off technology. (Paper number IAF-ICOSP89-4-9.) 5. NUCLEAR SPACE POWER TECHNOLOGIES 5-5. Advanced Heat Pipe Technology for Space Heat Transport and Rejection Technologies G. Y. Eastman Heat pipe technology is playing an increasingly important role in many of the future space power systems currently being evaluated. The importance of the heat pipe to these systems becomes clear when one considers the fact that over 50% of the mass in many of these systems is in the thermal management subsystem, with the heat pipe being the principal component of the subsystem. This paper describes several of the areas where the heat pipe is currently being considered for application as well as the principal areas of heat pipe development which will lead to significant changes in the way space system designers utilize and apply the heat pipe. New technology development, simulated by the highest and broadest level of heat pipe interest and funding support ever, has resulted in an order of magnitude improvement in thermal performance in a number of areas. One area of great interest is the evaporator input power density capability. Improved understanding of the operational mechanics of the heat pipe, specifically the effect of vapour within the heat pipe wick structure, has led to the ability to design heat pipes which can operate at or beyond the power density and/or power throughput at which
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