The Grand Tour was a
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
program that would have sent two groups of robotic probes to all the planets of the
outer Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
. It called for four spacecraft, two of which would visit
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
,
Saturn
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
, and
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
, while the other two would visit Jupiter,
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
, and
Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
. The enormous cost of the project, around $1 billion, led to its cancellation and replacement with Mariner Jupiter-Saturn, which became the
Voyager program
The Voyager program is an American scientific program that employs two robotic interstellar probes, ''Voyager 1'' and ''Voyager 2''. They were launched in 1977 to take advantage of a favorable alignment of Jupiter and Saturn, to Flyby (spacef ...
.
Background
The concept of the Grand Tour began in 1964, when
Gary Flandro
Gary Arnold Flandro (born March 30, 1934 in Salt Lake City, Utah) is an American aerospace engineer who currently holds the Boling Chair of Excellence in Space Propulsion (Emeritus) at the University of Tennessee Space Institute. He is also the V ...
of the
Jet Propulsion Laboratory
The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States.
Founded in the 1930s by Caltech researchers, JPL is owned by NASA an ...
(JPL) noted that an alignment of
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
,
Saturn
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
,
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
, and
Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
that would occur in the late 1970s would enable a single spacecraft to visit all of the outer planets by using
gravity assist
In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the p ...
s. The particular alignment occurs once every 175 years. By 1966, JPL was promoting the project, noting it would allow a complete survey of the outer planets in less time and for less money than sending individual probes to each planet.
Grand Tour
In 1969, NASA created the Outer Planets Working Group, which favored the concept of two missions that would visit three planets each (including
Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
, which was considered a planet at the time). These missions were referred to as the Grand Tour. One would launch in 1977 and visit Jupiter, Saturn, and Pluto, while the other would launch in 1979 and visit Jupiter, Uranus, and Neptune. This would reduce total mission time compared to a single Grand Tour from over thirteen years to seven and a half years. The Working Group also called for the development of a new spacecraft to carry out the flyby missions.
[
] These probes, called Thermoelectric Outer Planets Spacecraft (TOPS), were being designed at JPL and featured an operational life of over ten years.
The plan was set out in a report by 23 scientists, released on August 3, 1969. The study panel was co-chaired by
James A. Van Allen of the University of Iowa and
Gordon J. F. MacDonald Gordon James Fraser MacDonald (July 30, 1929 – May 14, 2002) was an American geophysicist and environmental scientist, best known for his principled skepticism regarding continental drift (now called plate tectonics), involvement in the developmen ...
of the University of California, Santa Barbara. President Nixon gave White House support to the concept in a statement released on March 7, 1970.
By 1971, the estimated cost of Grand Tour was $750 to $900 million, plus over $100 million to launch the spacecraft. Congressional pressure, combined with internal competition from the recently approved
Space Shuttle program
The Space Shuttle program was the fourth human spaceflight program carried out by the U.S. National Aeronautics and Space Administration (NASA), which accomplished routine transportation for Earth-to-orbit crew and cargo from 1981 to 2011. Its ...
, led to the decision to cancel the project in December 1971. The Grand Tour and TOPS were replaced with a proposal to visit only two planets using a pair of
Mariner
A sailor, seaman, mariner, or seafarer is a person who works aboard a watercraft as part of its crew, and may work in any one of a number of different fields that are related to the operation and maintenance of a ship.
The profession of the s ...
-derived probes.
Mariner Jupiter-Saturn
The Mariner Jupiter-Saturn project was approved in early 1972, with an estimated cost of less than $360 million for each of two probes.
The probes would be built by JPL, with the intention that they would last long enough to complete the original Grand Tour of the four giant planets, but be advertised as missions to only Jupiter and Saturn to reduce estimated total project costs.
The probes were to visit Jupiter, Saturn, and Saturn's moon
Titan. Titan was a valuable target, as it was the only moon known to have an atmosphere, and a flyby would gather information that would not otherwise be obtainable, including the density, composition, and temperature of the atmosphere.
Two trajectories were selected. One was designated JST: its mission would take it to Jupiter, Saturn, and Titan, with the probe's trajectory designed to optimize the Titan flyby. The second was designated JSX: it would be launched on a trajectory that would preserve the option of a Grand Tour, while serving as backup for the first probe. It would arrive after JST, and if JST were successful, it could continue with the Grand Tour. If JST was unsuccessful, JSX could be diverted to perform the Titan flyby itself, which would eliminate the possibility of a Grand Tour.
In March 1977, just a few months before launch, NASA held a competition to rename the project.
Voyager
![Titan's thick haze layer-picture from voyager1](https://upload.wikimedia.org/wikipedia/commons/c/c7/Titan%27s_thick_haze_layer-picture_from_voyager1.jpg)
The two spacecraft that launched retained the same mission concept. ''
Voyager 1
''Voyager 1'' is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and interstellar space beyond the Sun's heliosphere. Launched 16 days after its twin ''Voyager 2'', ''Voya ...
''
's course was optimized for the Titan flyby and ''
Voyager 2
''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, ''Voyager 1'', on a ...
'' for the Grand Tour. ''Voyager 2'' would reach Saturn nine months after ''Voyager 1'', giving plenty of time to decide if it should proceed with the Grand Tour. Additionally, by launching ''Voyager 2'' first, ''Voyager 1''
's launch could be re-targeted to perform the Grand Tour if ''Voyager 2'' were lost in a launch failure.
An option to skip ''Voyager 1''
's Titan flyby and proceed from Saturn to Pluto was identified, though Titan was still considered the more interesting target, especially after images from ''
Pioneer 11
''Pioneer 11'' (also known as ''Pioneer G'') is a robotic space probe launched by NASA on April 5, 1973, to study the asteroid belt, the environment around Jupiter and Saturn, solar winds, and cosmic rays. It was the first probe to encounter ...
'' indicated a very substantial atmosphere.
Though atmospheric haze obscured any images of Titan's surface, ''Voyager 1''
's flyby obtained valuable information about the moon, including data that offered compelling evidence for the existence of liquid hydrocarbon lakes on Titan's surface. With ''Voyager 1''
's mission complete,'' Voyager 2'' was cleared for an extended mission to Uranus and Neptune, fulfilling the goal of a Grand Tour as proposed in 1964.
The planets originally to be visited in the Grand Tour
File:Jupiter System Montage - GPN-2000-000451.jpg, Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
(''Voyager 1'', March 1979)
File:Saturn (planet) large.jpg, Saturn
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
(''Voyager 2'', August 1981)
File:Uranus.jpg, Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
(''Voyager 2'', January 1986)
File:Neptune - Voyager 2 (29347980845) flatten crop.jpg, Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
(''Voyager 2'', August 1989)
File:Nh-pluto-in-true-color 2x.jpg, Pluto
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
(image from ''New Horizons
''New Horizons'' is an Interplanetary spaceflight, interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research ...
'' mission, July 2015)
Note: Pluto was still classified as a planet when the Grand Tour was proposed and at the time ''New Horizons'' was launched.
See also
*
Interplanetary Transport Network
The Interplanetary Transport Network (ITN) is a collection of gravitationally determined pathways through the Solar System that require very little energy for an object to follow. The ITN makes particular use of Lagrange points as locations whe ...
References
External links
The Outer Solar System: A Program for ExplorationReport of a Study by the Space Science Board, June 1969
{{Voyager program
NASA programs
Voyager program