lpetrich
Contributor
The Case for Visiting the Outer Planets – Space Time – Medium The only spacecraft to have visited Uranus and Neptune is Voyager 2, in 1986 and 1989 respectively.
Those planets are nowadays called ice giants instead of gas giants, because much of their bulk is water. Much of that water is likely frozen as high-pressure phases of ice.
I checked on sections "A.4.1 Chemical Trajectories for Uranus" and "A.4.2 Chemical Trajectories for Neptune" and "A.4.3 SEP Trajectories for Uranus" and "", with "A.8.1 Uranus" and "A.8.2 Neptune" going into more detail. All these trajectories involve gravity assists, with flybys of Venus, the Earth, Mars, Jupiter, and/or Saturn.
For Uranus, the best case is launching in 2031 - 2033, using a Jupiter gravity assist, and arriving 11 years later (2042 - 2044). Jupiter-assist opportunities recur every 14 years, so the next one is in 2045 - 2047.
For Neptune, the best case is launching in 2029 - 2031, using a Jupiter gravity assist, and arriving 13 years later (2042 - 2044). Jupiter-assist opportunities recur every 13 years, so the next one is in 2042 - 2044.
SEP = Solar Electric Propulsion, with ion engines.
The document's authors considered a Uranus flyby with atmospheric probe, a Uranus orbiter with and without one, and a Neptune orbiter with one.
From last year is [1807.08769] Outer Solar System Exploration: A Compelling and Unified Dual Mission Decadal Strategy for Exploring Uranus, Neptune, Triton, Dwarf Planets, and Small KBOs and Centaurs
Recommends two missions: a Uranus / KBO flyby, optionally including an atmospheric probe, and a Neptune orbiter with an atmospheric probe. The Neptune orbiter will do over 10 flybys of Neptune's big moon Triton, an icy moon almost as large as the Earth's Moon.
The two spacecraft may be launched together on the same rocket, separating after a Jupiter flyby.
Those planets are nowadays called ice giants instead of gas giants, because much of their bulk is water. Much of that water is likely frozen as high-pressure phases of ice.
I checked on this issue, and I found Ice Giants Mission Planning with Ice Giant Pre-Decadal Mission Study Report from June 2017.
I checked on sections "A.4.1 Chemical Trajectories for Uranus" and "A.4.2 Chemical Trajectories for Neptune" and "A.4.3 SEP Trajectories for Uranus" and "", with "A.8.1 Uranus" and "A.8.2 Neptune" going into more detail. All these trajectories involve gravity assists, with flybys of Venus, the Earth, Mars, Jupiter, and/or Saturn.
For Uranus, the best case is launching in 2031 - 2033, using a Jupiter gravity assist, and arriving 11 years later (2042 - 2044). Jupiter-assist opportunities recur every 14 years, so the next one is in 2045 - 2047.
For Neptune, the best case is launching in 2029 - 2031, using a Jupiter gravity assist, and arriving 13 years later (2042 - 2044). Jupiter-assist opportunities recur every 13 years, so the next one is in 2042 - 2044.
SEP = Solar Electric Propulsion, with ion engines.
The document's authors considered a Uranus flyby with atmospheric probe, a Uranus orbiter with and without one, and a Neptune orbiter with one.
From last year is [1807.08769] Outer Solar System Exploration: A Compelling and Unified Dual Mission Decadal Strategy for Exploring Uranus, Neptune, Triton, Dwarf Planets, and Small KBOs and Centaurs
Recommends two missions: a Uranus / KBO flyby, optionally including an atmospheric probe, and a Neptune orbiter with an atmospheric probe. The Neptune orbiter will do over 10 flybys of Neptune's big moon Triton, an icy moon almost as large as the Earth's Moon.
The two spacecraft may be launched together on the same rocket, separating after a Jupiter flyby.