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. A part of the Voyager program, it was launched 16 days before its twin, Voyager 1, on a trajectory that took longer to reach gas giants Jupiter and Saturn but enabled further encounters with ice giants Uranus and Neptune. Voyager 2 remains the only spacecraft to have visited a combination of either of the gas giants and both ice giant planets. Voyager 2 was the fourth of five spacecraft to achieve Solar escape velocity, which allowed it to leave the Solar System.
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 fly near them while collecting data for transmission back to Earth. After launch the decision was taken to send Voyager 2 near Uranus and Neptune to collect data for transmission back to Earth.
In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the 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.
New Horizons is an 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 Institute (SwRI), with a team led by Alan Stern, the spacecraft was launched in 2006 with the primary mission to perform a flyby study of the Pluto system in 2015, and a secondary mission to fly by and study one or more other Kuiper belt objects (KBOs) in the decade to follow, which became a mission to 486958 Arrokoth. It is the fifth space probe to achieve the escape velocity needed to leave the Solar System.
Mariner Mark II was NASA's planned family of unmanned spacecraft for the exploration of the outer Solar System that were to be developed and operated by JPL between 1980 through the year 2010.
The Grand Tour was 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 New Frontiers program is a series of space exploration missions being conducted by NASA with the purpose of furthering the understanding of the Solar System. The program selects medium-class missions which can provide high science returns.
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.
Neptune has been directly explored by one space probe, Voyager 2, in 1989. As of April 2022, 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.
Neptune is the eighth planet from the Sun and the farthest known solar planet. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, and slightly more massive than its near-twin Uranus. Neptune is denser and physically smaller than Uranus because its greater mass causes more gravitational compression of its atmosphere. It is referred to as one of the solar system's two ice giant planets.
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.
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.
The Planetary Science Decadal Survey is a publication of the United States National Research Council produced for NASA and other United States Government Agencies such as the National Science Foundation. The document identifies key questions facing planetary science and outlines recommendations for space and ground-based exploration ten years into the future. Missions to gather data to answer these big questions are described and prioritized, where appropriate. Similar decadal surveys cover astronomy and astrophysics, earth science, and heliophysics.
The Uranus Orbiter and Probe is an orbiter mission concept to study Uranus and its moons. The orbiter would also deploy an atmospheric probe to characterize Uranus's atmosphere. The concept is being developed as a potential large strategic science mission for NASA. The current proposal targets a launch in 2031 using a Falcon Heavy expendable launch vehicle with a gravity assist at Jupiter allowing arrival at Uranus in 2044. The science phase would last 4.5 years and include multiple flybys of each of the major moons.
New Horizons 2 was a proposed mission to the trans-Neptunian objects by NASA. It was conceived as a planetary flyby mission in 2002, based on the New Horizons spacecraft, which was in development at the time. In March 2005, the proposal was not selected for further development because of a shortage of plutonium-238 needed for the radioisotope thermoelectric generator (RTG). The New Horizons 2 study was funded out of the New Frontiers program, and was delivered to the U.S. Congress in June 2005.
Trident is a space mission concept to the outer planets proposed in 2019 to NASA's Discovery Program. The concept includes flybys of Jupiter and Neptune with a focus on Neptune's largest moon Triton.
Neptune Odyssey is an orbiter mission concept to study Neptune and its moons, particularly Triton. The orbiter would enter into a retrograde orbit of Neptune to facilitate simultaneous study of Triton and would launch an atmospheric probe to characterize Neptune's atmosphere. The concept is being developed as a potential large strategic science mission for NASA by a team led by the Applied Physics Laboratory at Johns Hopkins University. The current proposal targets a launch in 2033 using the Space Launch System with arrival at Neptune in 2049, although trajectories using gravity assists at Jupiter have also been considered with launch dates in 2031.
Interstellar Express or Interstellar Heliosphere Probe is the current name for a proposed Chinese National Space Administration program designed to explore the heliosphere and interstellar space. The program will feature two 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.
