Voyager 2
1977
The only spacecraft ever to visit Uranus and Neptune - the only one ever to lay eyes on any ice giant. Launched 20 August 1977 (sixteen days before its twin Voyager 1, but on the slower, outer track), it turned a rare outer-planet alignment that recurs every ~176 years into a tour of four worlds, then crossed into interstellar space on 5 November 2018.
Specs
Mass 825 kg; encounters: Jupiter 1979, Saturn 1981, Uranus 24 January 1986, Neptune 25 August 1989; each flyby timed to bend the trajectory toward the next planet - a gravity assist chain that no other window makes possible this century. Science today: cosmic-ray, magnetometer and plasma-wave instruments (NASA status table, 2026). Cameras off, like Voyager 1, to save power.
Why it matters
Every close-up picture of Uranus and Neptune that exists, exists because of this spacecraft - we have sent nothing else to either, before or since. It also taught remote repair: in 1986 a stuck scan platform was rescued by switching to backup flight software patched together on the ground within days - the ancestor of every rover fix made from a desk. And flown with its twin, it is the pair of instruments with the widest baseline ever deployed against the edge of the Solar System: two probes, two directions, one question.