1. Harold C. Urey, "The Chemistry of the Moon," Proceedings of the Lunar and Planetary Exploration Colloquium, Jet Propulsion Laboratory, Pasadena, Calif., October 29, 1958, Vol. I, No. 3, pp. 1-9
3. Albert R. Hibbs (ed.), Exploration of the Moon, the Planets, and Interplanetary Space, JPL Report No. .30-1 (Pasadena, Calif.: Jet Propulsion Laboratory, California Institute of Technology, April 30, 1959), pp. 93 95.
4. Project Ranger, Report of the Subcommittee on NASA Oversight of the Committee on Science and Astronautics, U.S. House of Representatives, June 16, 1964, p. 23. Three of the first six Ranger missions were not completed because of malfunctions in the launch vehicles, not the spacecraft. Moreover, Ranger flew on NASAís first Atlas-Agena launch vehicle with all of the problems entailed in proving a new system. Finally, it is fair to state that the Mercury Program took priority over Ranger in the selection of Atlas rockets as launch vehicles.