The Grand Tour Outer Planets mission is proposed to NASA by the Jet Propulsion Laboratory. Using a combination of the gravitational assist trajectories computed by JPL’s Michael Minovitch in 1961, Caltech/JPL grad student Gary Flandro has identified a favorable alignment of the outer planets which would allow for a single spacecraft to reach Jupiter, Saturn, Uranus, Neptune and Pluto within two decades. Vehicles taking advantage of this planetary alignment must lift off at very precise times during 1977 and 1978, and the alignment will not occur again for nearly 200 years. An ambitious plan is laid out for multiple flyby vehicles with atmospheric probes for every gas planet and landers for specific moons of interest, launched by Saturn V rockets. Budget realities scale this plan back: flybys will be carried out by two cheaper Mariner vehicles (later renamed Voyager), while the atmospheric and satellite probes – eventually to be renamed Galileo and Cassini – wait even longer to reach their destinations, and the Pluto flyby is scrapped until the 21st century New Horizons probe lifts off. JPL also recommends an inner solar system tryout of the gravitational assist maneuvers required, resulting in the Mariner 10 mission to Venus and Mercury.
