The Grand Tour is a NASA program that would have sent two groups of robotic probes to all the planets of the outer Solar System. It called for four spacecraft, two of which would visit Jupiter, Saturn, and Pluto, while the other two would visit Jupiter, Uranus, and Neptune. 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 concept of the Grand Tour began in 1964, when Gary Flandro of the Jet Propulsion Laboratory (JPL) noted that an alignment of Jupiter, Saturn, Uranus, and Neptune that would occur in the late 1970s would enable a single spacecraft to visit all of the outer planets by using gravity assists. The particular alignment occurs once every 175 years. [1] 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.
In 1969, NASA created the Outer Planets Working Group, which favored the concept of two missions that would visit three planets each (including Pluto, 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. [2] : 256 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 of the University of California, Santa Barbara. [3] President Nixon gave White House support to the concept in a statement released on March 7, 1970. [4]
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, 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-derived probes. [2] : 260–261
The Mariner Jupiter-Saturn project was approved in early 1972, with an estimated cost of less than $360 million for each of two probes. [5] 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. [2] : 263
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. [6]
In March 1977, just a few months before launch, NASA held a competition to rename the project. [2] : 269
The two spacecraft that launched retained the same mission concept. Voyager 1 's course was optimized for the Titan flyby and Voyager 2 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. [6] : 155 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 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.
Note: Pluto was still classified as a planet when the Grand Tour was proposed and at the time New Horizons was launched.
The Mariner program was conducted by the American space agency NASA to explore other planets. Between 1962 and late 1973, NASA's Jet Propulsion Laboratory (JPL) designed and built 10 robotic interplanetary probes named Mariner to explore the inner Solar System – visiting the planets Venus, Mars and Mercury for the first time, and returning to Venus and Mars for additional close observations.
Pioneer 11 is a NASA robotic space probe launched on April 5, 1973, to study the asteroid belt, the environment around Jupiter and Saturn, the solar wind, and cosmic rays. It was the first probe to encounter Saturn, the second to fly through the asteroid belt, and the second to fly by Jupiter. Later, Pioneer 11 became the second of five artificial objects to achieve an escape velocity allowing it to leave the Solar System. Due to power constraints and the vast distance to the probe, the last routine contact with the spacecraft was on September 30, 1995, and the last good engineering data was received on November 24, 1995.
Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is currently carried out mainly by astronomers with telescopes, its physical exploration is conducted both by uncrewed robotic space probes and human spaceflight. Space exploration, like its classical form astronomy, is one of the main sources for space science.
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 the interstellar space beyond the Sun's heliosphere. It was launched 16 days after its twin, Voyager 2. It communicates through the NASA Deep Space Network (DSN) to receive routine commands and to transmit data to Earth. Real-time distance and velocity data are provided by NASA and JPL. At a distance of 164.0 AU from Earth as of August 2024, it is the most distant human-made object from Earth. The probe made flybys of Jupiter, Saturn, and Saturn's largest moon, Titan. NASA had a choice of either doing a Pluto or Titan flyby; exploration of the moon took priority because it was known to have a substantial atmosphere. Voyager 1 studied the weather, magnetic fields, and rings of the two gas giants and was the first probe to provide detailed images of their moons.
Voyager 2 is a space probe launched by NASA on August 20, 1977, as a part of the Voyager program. It was launched on a trajectory towards the gas giants Jupiter and Saturn and enabled further encounters with the ice giants Uranus and Neptune. It remains the only spacecraft to have visited either of the ice giant planets, and was the third of five spacecraft to achieve Solar escape velocity, which will allow it to leave the Solar System. It has been sending scientific data to Earth for 47 years, 14 days, making it the oldest active space probe. Launched 16 days before its twin Voyager 1, the primary mission of the spacecraft was to study the outer planets and its extended mission is to study interstellar space beyond the Sun's heliosphere.
The Voyager program is an American scientific program that employs two interstellar probes, Voyager 1 and Voyager 2. They were launched in 1977 to take advantage of a favorable alignment of the two gas giants Jupiter and Saturn and the ice giants, Uranus and Neptune, to fly near them while collecting data for transmission back to Earth. After launch, the decision was made to send Voyager 2 near Uranus and Neptune to collect data for transmission back to Earth.
A gravity assist, gravity assist maneuver, swing-by, or generally a gravitational slingshot in orbital mechanics, is a type of spaceflight flyby which makes use of the relative movement and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft, typically to save propellant and reduce expense.
Mariner Mark II was NASA's planned family of uncrewed spacecraft for the exploration of the outer Solar System that were to be developed and operated by JPL between 1980 through the year 2010.
Gary Arnold Flandro is an American aerospace engineer who is currently the professor for the Boling Chair of Excellence in Space Propulsion (Emeritus) at the University of Tennessee Space Institute. He is also the Vice President and Chief Engineer for Gloyer-Taylor Laboratories (GTL).
The exploration of Uranus has, to date, been through telescopes and a lone probe by NASA's Voyager 2 spacecraft, which made its closest approach to Uranus on January 24, 1986. Voyager 2 discovered 10 moons, studied the planet's cold atmosphere, and examined its ring system, discovering two new rings. It also imaged Uranus' five large moons, revealing that their surfaces are covered with impact craters and canyons.
The exploration of Saturn has been solely performed by crewless probes. Three missions were flybys, which formed an extended foundation of knowledge about the system. The Cassini–Huygens spacecraft, launched in 1997, was in orbit from 2004 to 2017.
Neptune has been directly explored by one space probe, Voyager 2, in 1989. As of 2024, there are no confirmed future missions to visit the Neptunian system, although a tentative Chinese mission has been planned for launch in 2024. NASA, ESA, and independent academic groups have proposed future scientific missions to visit Neptune. Some mission plans are still active, while others have been abandoned or put on hold.
Discovery and exploration of the Solar System is observation, visitation, and increase in knowledge and understanding of Earth's "cosmic neighborhood". This includes the Sun, Earth and the Moon, the major planets Mercury, Venus, Mars, Jupiter, Saturn, Uranus, and Neptune, their satellites, as well as smaller bodies including comets, asteroids, and dust.
Spaceflight in 1977 included some important events such as the roll out of the Space Shuttle orbiter, Voyager 1 and Voyager space probes were launched. NASA received the Space Shuttle orbiter later named Enterprise, on 14 January. This unpowered sub-orbital space plane was launched off the top of a modified 747 and was flown uncrewed until 13 August until a human crew landed the Enterprise for the first time.
The exploration of Pluto began with the arrival of the New Horizons probe in July 2015, though proposals for such a mission had been studied for many decades. There are no plans as yet for a follow-up mission, though follow-up concepts have been studied.
Argo was a 2009 spacecraft mission concept by NASA to the outer planets and beyond. The concept included flybys of Jupiter, Saturn, Neptune, and a Kuiper belt object. A focus on Neptune and its largest moon Triton would have helped answer some of the questions generated by Voyager 2's flyby in 1989, and would have provided clues to ice giant formation and evolution.
Shensuo, formerly Interstellar Express, is a proposed Chinese National Space Administration program designed to explore the heliosphere and interstellar space. The program will feature two or three space probes that will purportedly be launched in 2024 and follow differing trajectories to encounter Jupiter to assist them out of the Solar System. The first probe, IHP-1, will travel toward the nose of the heliosphere, while the second probe, IHP-2, will fly near to the tail, skimming by Neptune and Triton in January 2038. There may be another probe—tentatively IHP-3—which would launch in 2030 to explore to the northern half of the heliosphere. IHP-1 and IHP-2 would be the sixth and seventh spacecraft to leave the Solar System, as well as first non-NASA probes to achieve this status.
Interstellar Probe (ISP) is a proposed NASA space probe designed to explore and characterize the heliosphere and interstellar space. The study was originally proposed in 2018 by NASA for the Applied Physics Laboratory. It would have a baseline launch between 2036 and 2041. The probe would launch on a direct hyperbolic trajectory to encounter Jupiter after six to seven months, after which the probe would travel at a speed of about 6–7 astronomical units (900,000,000–1.05×109 kilometres) per year, leaving the heliosphere after only 16 years.
The sending of the unmanned "grand tour" craft on cruises to the outer planets — Jupiter, Saturn, Uranus, Neptune and Pluto — in 1977 and 1979. Such probes, which could take a decade or longer to complete, have long been proposed by scientists because the alignment of the planets will not favor such an effort again for about 180 years after this decade. Mr. Nixon's announcement was the first giving White House support to the attempt.