lasing gas mixture of CO2 and He was exposed to 1500°K thermal radiation for brief periods of time. A peak gain coefficient of 2.8 X 10-3 cm-1 was measured at 10.6 // wavelength and 1 Torr of pressure. A simple analytical model is used to describe the rate of change of energy distribution of the vibrational modes of CO2 and to predict the gain. Good agreement is found between predictions and the experimental data. The experimental results suggest that the maximum overall efficiency of the blackbody-pumped CO2 laser system is of the order of 12%. (Paper number IAF-ICOSP89-7-5.) 7-7. Surveying the Future of International Commercial Space Power Todd B. Hawley USA. This paper includes the results of a two-round Delphi survey conducted with over 30 world experts in the field of industrial space power, and demonstrates projections for the commercial development of this field over the next 50 years. The experts surveyed converged strongly with regard to the development of small-scale and larger-scale space power plants in orbit, beginning with a 500-kW demonstration model in low Earth orbit and culminating in the construction of 10, five-Gw Solar Power Satellites in geosynchronous orbit in the 2030s. Among the major conclusion reached in the survey regarding the use of non-terrestrial materials, primarily lunar-derived construction and propellant, which was determined to be the most critical element in the commercialization of multi-gigawatt SPS. Up to 67% of the construction mass of multi-gigawatt SPS would come from non-terrestrial materials, according to the surveyed experts. The final conclusion of the paper indicates that a steady development of space power technologies by an international consortium could be the most effective means available to commercialize space power, and that such commercialization would take place in a competitive manner within the next five decades. (Paper number IAF-ICOSP89-7-7.) 8. ADVANCED NUCLEAR SPACE POWER SYSTEMS CONCEPTS 8-6. Space Nuclear Reactor Shields for Manned and Unmanned Applications Barbara I. McKissock & Harvey S. Bloomfield NASA Lewis Research Center, Cleveland, OH 44135, USA. Missions which use nuclear reactor power systems require radiation shielding of payload and/or crew areas to predetermined dose rates. Since shielding can become a significant fraction of the total mass of the system, it is of interest to show the effect of various parameters on shield thickness and mass for manned and unmanned applications. Algorithms were developed to give the thicknesses needed if reactor thermal power, separation distances, and dose rates are given as input. The thickness algorithms were combined with models for four different shield geometries to allow tradeoff studies of shield volume and mass for a variety of manned and unmanned missions. Shield design tradeoffs presented in this study include the effects of: higher allowable dose rates; radiation-hardened electronics; shorter crew exposure times; shield geometry; distance of the payload and/or crew from the reactor; and changes in the size of the shielded area. Specific NASA missions that were considered in this study include unmanned outer planetary exploration, manned advanced/ evolutionary space station, and advanced manned lunar base. (Paper number IAF- ICOSP89-8-6.)
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