Planetary Grand Tour

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For other uses, see Grand Tour (disambiguation).
The trajectories that enabled NASA's Voyager 1 and 2 spacecraft to tour the four gas giant planets and achieve velocity to leave the Solar System.
Voyager 1 's close view of Titan, attempted in place of a Pluto flyby.

The Planetary Grand Tour was a plan to send unmanned probes to the planets of the outer Solar System. Conceived by Gary Flandro of the Jet Propulsion Laboratory in 1964,[1][2] the Grand Tour would exploit the alignment of Jupiter, Saturn, Uranus, Neptune, and Pluto, an event that would occur in the late 1970s and not recur for 175 years.[3]


A probe could use Jupiter as a gravitational slingshot to extend its trajectory to the outer Solar System, a solution provided by Michael Minovitch working on the three-body problem in 1961. President Kennedy approved preliminary planning of such a mission.

Mariners 11 through 14[edit]

The original proposed mission design included four probes. The first two, with proposed launch dates in 1976 and 1977, were to fly by Jupiter, Saturn, and Pluto. The other two, with proposed launch dates in 1979, were to fly by Jupiter, Uranus, and Neptune.[citation needed] These were dubbed "Mariner Mark II" and were considered part of that program. The vehicles' systems were to be multiply redundant to ensure reliability for up to 12 years.

The Voyager project[edit]

NASA budget cuts threatened to doom the Grand Tour missions in 1972, cancelling Mariners 12 and 14. Renamed Voyager, the remaining probes were only supposed to go to Jupiter and Saturn. The two Voyager probes, launched in 1977, were originally meant to fly by Jupiter and Saturn. The Voyager 2 mission used the fortunate alignments of the outer planets and was extended to include close flybys of both Uranus and Neptune. Voyager 2's mission has come to be regarded as the "Grand Tour".

Voyager 1 could have been sent to Pluto after Saturn but was instead sent to fly by Titan; Voyager 2's trajectory could not be altered to bring the probe by Pluto after the Neptune flyby in 1989.

Pluto remained unexplored until the New Horizons spacecraft flew by it and its five known moons on July 14, 2015.[4]

The planets originally to be visited in the Grand Tour[edit]

See also[edit]


  1. ^ Flandro, G. (1966). "Fast reconnaissance missions to the outer solar system utilizing energy derived from the gravitational field of Jupiter". Astronaut. Acta 12: 329–337. 
  2. ^ Flandro, Gary. "Fast Reconnaissance Missions To The Outer Solar System Using Energy Derived From The Gravitational Field Of Jupiter" (PDF). NASA-JPL Contract #7-100. 
  3. ^ Butrica, Andrew J. (1998). Mack, Pamela E., ed. From Engineering Science to Big Science: The NACA and NASA Collier Trophy Research Project Winners. Washington, D.C.: NASA. ISBN 978-1-4102-2531-3 Archived from the original on 2014-08-25. Retrieved 2014-08-25.  Missing or empty |title= (help); |chapter= ignored (help)
  4. ^ Dunn, Marcia (14 July 2015). "Pluto close-up: Spacecraft makes flyby of icy, mystery world". AP News. Retrieved 14 July 2015. 
  • Weaver, Kenneth F. "Voyage to the Planets.' National Geographic, volume 138, number 2 (August 1970), pp. 147–193.