Planetary Grand Tour
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, 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. 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.
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.
The vehicles' systems were to be multiply redundant to ensure reliability for up to 12 years.
NASA budget cuts eventually doomed the Grand Tour missions in 1972, along with 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 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.
The New Horizons spacecraft is scheduled to fly-by Pluto and its five known moons in 2015.
- 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.
- Flandro, Gary. "Fast Reconnaissance Missions To The Outer Solar System Using Energy Derived From The Gravitational Field Of Jupiter". NASA-JPL Contract #7-100. GravityAssist.com.
- Butrica, Andrew J. "Voyager: The Grand Tour of Big Science".
- Weaver, Kenneth F. "Voyage to the Planets.' National Geographic, volume 138, number 2 (August 1970), pp. 147–193.
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