for planetary landing missions, TR 32-231, Jet Propulsion Lab., Pasadena, Calif. (May 1, 1962). 3 Speiser, E. W., Performance of nuclear-electric propulsion systems in space exploration, TR 32-159, Jet Propulsion Lab., Pasadena, Calif. (December 15, 1961). 4 Stearns, J. W., Electric propulsion requirements for planetary and interplanetary spacecraft, TR 32-403, Jet Propulsion Lab., Pasadena, Calif, (to be published). 5 Hayes, R. J., Hoffman, M. A., and Stuhlinger, E., The manned electric rocket challenge, Preprint 2222-61, ARS Space Flight Report to the Nation, New York (October 1961). 6 Melbourne, W. G. and Sauer, C. G., Optimum thrust programs for power-limited propulsion systems, TR 32-118, Jet Propulsion Lab., Pasadena, Calif. (June 15, 1961). 7 Volkoff, J. J., Protection requirements for the resistance of meteorite penetration of interplanetary spacecraft systems, TR 32-410, Jet Propulsion Lab., Pasadena, Calif, (to be published). 8 Davis, J. P., A nuclear reactor concept for electric propulsion application, TR 32-385, Jet Propulsion Lab., Pasadena, Calif. (March 4, 1963).