Interestingly, the voyager missions were also timed-events -- they were launched when they were because JPL realized it was a 1-in-175-year alignment of the ou

Interestingly, the voyager missions were also timed-events -- they were launched when they were because JPL realized it was a 1-in-175-year alignment of the outer planets that made it feasible to launch just a few crafts to visit the outer planets all in one go: https://en.wikipedia.org/wiki/Grand_Tour_program https://en.wikipedia.org/wiki/Grand_Tour_program