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2. W. E. Moeckel: Fast Interplanetary Missions with Low-Thrust Propulsion Systems; NASA TR R-79, 1961.
3. J. W. Stearns: Electro-Propulsion System Application; Astronautics, vol. 7, March 1962.
4. L. Rosenblum and R. English: Nuclear-Electric Systems in Space; Proc. of Seminar on Advanced Energy Sources and Conversion Techniques, ASTIA AD 209301, Nov. 3-7, 1958, Pasadena, Calif.
5. W. D. Weatherford, Jr., J. C. Tyler, and P. M. Ku: Properties of Inorganic Energy Conversion and Heat Transfer Fluids for Space Applications; TR 61-96, WADD, Nov. 1961.