The Planetary Grand Tour was an ambitious plan to send unmanned probes to the planets of the outer solar system. Conceived by Gary Flandro of the Jet Propulsion Laboratory in the late 1960s, 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 175 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.
The original proposed mission design had 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.
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. 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 specifically come to be regarded as the "Grand Tour."
Voyager 1 could have been sent to Pluto after Saturn, but was instead sent on a trajectory which brought it close by Titan, eliminating the Pluto flyby. Voyager 2's trajectory could not be bent to bring the probe by Pluto after the Neptune flyby in 1989.
Pluto is scheduled for exploration by the New Horizons spacecraft set to fly by the dwarf planet and its five known moons in 2015.
Famous quotes containing the words planetary, grand and/or tour:
“What is a television apparatus to man, who has only to shut his eyes to see the most inaccessible regions of the seen and the never seen, who has only to imagine in order to pierce through walls and cause all the planetary Baghdads of his dreams to rise from the dust.”
—Salvador Dali (1904–1989)
“The great object of Education should be commensurate with the object of life. It should be a moral one; to teach self-trust: to inspire the youthful man with an interest in himself; with a curiosity touching his own nature; to acquaint him with the resources of his mind, and to teach him that there is all his strength, and to inflame him with a piety towards the Grand Mind in which he lives. Thus would education conspire with the Divine Providence.”
—Ralph Waldo Emerson (1803–1882)
“Left Washington, September 6, on a tour through Ohio, Kentucky, Tennessee, Georgia, and Virginia.... Absent nineteen days. Received every where heartily. The country is again one and united! I am very happy to be able to feel that the course taken has turned out so well.”
—Rutherford Birchard Hayes (1822–1893)