military and civilian applications, whether they are the same, the conditions that cause them to differ, and the realism of the scenarios that cause similarities or differences. (Paper number IAF-ICOSP89-2-1.) Note: * This work was performed at Sandia National Laboratories, which is operated for the US Department of Energy under contract number DE-AC04-76DP00789. A portion of the work was performed at NASA's Lewis Research Center in a team effort with Sandia National Laboratories. 2-2. CNES-CEA Comparative Evaluation Study of Various Candidate 20 kWe Space Power Systems F. Carre, E. Proust & P. Keirle Commissariat a I'Energie Atomique, Centre d'Etudes Nucleaires de Saclay, 91191 Gif-sur- Yvette Cedex, France (Tel: 33 (1) 69 08 54 04). A preliminary comparison study of various candidate 20 kWe space power systems, likely to meet the projected electric needs of the first European space missions from year 2005 onward, has been conducted within the framework of the cooperative program between the French Centre National d'Etudes Spatiales (CNES) and the Commissariat a I'Energie Atomique (CEA) about space nuclear power systems. The candidate power systems include the radioisotopic generators with either thermoelectric or Brayton conversion, the solar generators with either photovoltaic or Brayton conversion, and the nuclear power systems. The performances of the various space power sources are evaluated according to a list of criteria including launch safety, required development effort, estimated recurrent cost, extrapolation potential, and also important features for the integration into the future European launcher (Ariane V) and for the in-orbit operation, such as complexity of startup scenario, and operational reliability over a 7-year lifetime. Both types of radioisotopic generators are excluded from the final recommendation, for the excessive mass of plutonium 238 required for 20 kWe systems (from 210 to 650 kg, depending on the conversion efficiency), and for the resulting consequences on the recurrent cost of the generator, and on the potential threat for the environment, exposed to contamination with plutonium in case of launch abort or reentry from earth orbit. The solar dynamic conversion system, which was only investigated in a dual version for stability of the platform attitude, is also discarded for its excessive mass and volume characteristics, which exclude the simultaneous integration of a payload satellite into the Ariane V launcher. The best candidates emerging from the study, are the solar photovoltaic generator with GaAs cells and nickel/hydrogen batteries, and the nuclear power system, which both exhibit comparable performances, in terms of total mass (about 2200 kg), reliability over a 7-year lifetime, and compatibility with a payload satellite for integration into Ariane V. The major advantages of the nuclear power system, in comparison with the solar photovoltaic alternative, relate to the orbit independent operating mode, to the large extrapolation and survivability potential, and to the relatively modest recurrent cost subject to a weak dependence only on the design power. (Paper number IAF-ICOSP89-2-2.) 2-3. A Review of Nuclear Electric Propulsion Spacecraft System Concepts* IF. D. Deininger & K. T. Nock Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA. The past 25-30 years of system concepts and design philosophies for spacecraft employing nuclear electric propulsion are reviewed. Nuclear electric propulsion (NEP) spacecraft system design constraints and criteria are identified including radiation exposure of humans and
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