James M. Naughton (March 8, 1970). “Nixon asks start of a 'grand tour' of planets in '77”. The New York Times. http://timesmachine.nytimes.com/timesmachine/1970/03/08/129337852.html. "The sending of the unmanned “grand tour” craft on cruises to the outer planets — Jupiter, Saturn, Uranus, Neptune and Pluto — in 1977 and 1979. Such probes, which could take a decade or longer to complete, have long been proposed by scientists because the alignment of the planets will not favor such an effort again for about 180 years after this decade. Mr. Nixon's announcement was the first giving White House support to the attempt."
