The Planetary Grand Tour was an ambitious plan to send unmanned probes to the outermost planets of the solar system. Conceived by Gary Flandro of the Jet Propulsion Laboratory, the Grand Tour would have exploited the alignment of Jupiter, Saturn, Uranus, Neptune, and Pluto, an event that would occur in the late 1970s, and not recur for 176 years. A probe sent to Jupiter could use that planet as a gravitational slingshot to extend its trajectory to planets further out in the Solar System. Grand Tour can refer to: A tour of European cultural centers, once a standard feature of the education of the British elite. ... Gary Flandro, PhD is an American aerospace engineer who currently holds the Boling Chair of Excellence in Space Propulsion at the University of Tennessee Space Institute. ... For the singer/songwriter, see Jon Peter Lewis. ... For other uses, see Jupiter (disambiguation). ... This article is about the planet. ... For other uses, see Uranus (disambiguation). ... For other uses, see Neptune (disambiguation). ... For other uses, see Pluto (disambiguation). ... In orbital mechanics and aerospace engineering, a gravitational slingshot or gravity assist is the use of the gravity of a planet or other celestial body to alter the path and speed of a spacecraft. ...

The original proposed mission design had four probes. The first two, launched in 1976 and 1977, would fly by Jupiter, Saturn, and Pluto. The other two, launched in 1979, would fly by Jupiter, Uranus, and Neptune. For other uses, see Jupiter (disambiguation). ... This article is about the planet. ... For other uses, see Pluto (disambiguation). ... For other uses, see Jupiter (disambiguation). ... For other uses, see Uranus (disambiguation). ... For other uses, see Neptune (disambiguation). ...

The vehicles were to have been designed with multiple redundant systems to ensure reliability over missions lasting up to 12 years.

NASA budget cuts eventually doomed the Grand Tour missions in 1972, as well as later proposals for a "mini grand tour". However, many elements of the Grand Tour were added to the Voyager program. The two Voyager probes, launched in 1977, were originally meant to fly by Jupiter and Saturn. But Voyager 2 used the fortunate alignments of the outer planets and was able to add close flybys of both Uranus and Neptune. Voyager 2's mission has specifically come to be regarded as the "Grand Tour." For other uses, see NASA (disambiguation). ... Voyager Project redirects here. ... For other uses, see Jupiter (disambiguation). ... This article is about the planet. ... Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ... For other uses, see Neptune (disambiguation). ... Trajectory Voyager 2 is an unmanned interplanetary spacecraft, launched on August 20, 1977. ...

Voyager 1 could have been sent to Pluto after Saturn, but was instead sent on a trajectory which brought it close by Titan, eliminating Pluto. Voyager 2's trajectory could not be bent to bring the probe by Pluto after the Neptune flyby in 1989. Titan (, from Ancient Greek Τῑτάν) or Saturn VI is the largest moon of Saturn and the only moon known to have a dense atmosphere. ...

Pluto, no longer regarded as a planet after the 2006 redefinition, is scheduled for exploration by the New Horizons spacecraft set to rendezvous with the dwarf planet and its three moons in 2015. The final definition left the solar system with eight planets. ... For other uses, see New Horizons (disambiguation). ... Artists impression of Pluto (background) and Charon (foreground). ...

References

• See National Geographic, August 1970, for proposed Grand Tour project information.