Thought experiment: Launch windows and travel times for probes to Uranus and Neptune?

Thru luck of timing, we were able to take advantage of a once in 175-year planetary alignment to allow Voyager 2 to merrily hopscotch from Jupiter to Saturn to Uranus and then to Neptune.

Let’s say we don’t want to wait 175 years for the next Grand Tour, but we still wanted to send a probe to the Ice Giants.

Assume for this thought experiment we want to visit Uranus, and that we want at a minimum to swing by Jupiter for a little extra boost.

What would be the launch window(s) for that.

Same question for Neptune.

(If Saturn also happened to be in the correct place to facilitate either of those, that’s cool, but it doesn’t have to be.)

What would be the expected travel times. (Voyager 2 took nine years for Uranus, and 12 for Neptune.)
[I called it a ‘thought experiment’ because I realize there’s not a chance in heck we’ll ever see another probe to Uranus or Neptune in our lifetime. Not very interesting, too long for travel time, and too much competition for funding]

An answer to your question calls for a magician, not just a scientist. With a sufficiently-complicated trajectory, you can get pretty much anywhere with pretty much any configuration of planets. But finding just which complicated trajectory will do the job is a task which is very difficult for both computers and for the vast majority of humans. There are a small number of humans who are good at this task, but they generally can’t explain how they do it. It is, in that sense, black magic.

Gravity assisted trajectories can get quite complicated. To send the Gallileo probe to Jupiter it did a “VEEGA”: Venus-Earth-Earth Gravity Assist. I.e., it was sent to Venus first, then did two passes by Earth and then onto Jupiter.

Hence Chronos’ comment about the difficulty of coming up with them. Sure, going by several bodies, even repeating some, takes more time but then you don’t have to wait as long for a faster route. The specifics of what options are available, which ones to choose, trade-offs for launch time vs. transit time, etc. quickly become overwhelming.

Note that hardware trade-offs play a role. If you want to leave soon, you have to use off-the-shelf rockets, etc. But if you specially build something, it could get you there faster. But building and testing a new system takes a lot of time.

There isn’t a remotely simple answer to the question.

And this isn’t even getting into more complex things like the Interplanetary Transport Network, keyholes, etc.

Well, yeah, I realize that you can get some really complicated swingbys (Mercury MESSENGER was really intense) but. . .
New Horizons was designed for a straight shot to Jupiter without a lot of inner planet swingbys. If we had missed that launch window, the next one would be a year later–and it would lose Jupiter’s assistant, taking an extra three or four years to make it to Pluto.

So that’s why I was trying to keep it. . . eh. . . ‘simple.’ We could probably launch a probe ‘directly’ to Uranus or Neptune, and it would probably take at the most about 15 years. A Jupiter swingby would cut off time, but. . . if Jupiter would not be in a convenient place for another 20 years, we would have to settle for the <15 year trip.

Is this why Mechjeb’s pork chops are not as good as Scott Manley’s intuition?

Hmmm… I read the title of the OP as, “Launch Windows and…” I actually read this thread because I thought that the next version of Windows and travel through time and go to Neptune. Where, of course, I would immediately perish.

I don’t think so. Mechjeb’s “problems”, such as they are, are pretty much just that it only looks at Hohmann transfers. But Hohmann transfers are pretty much exactly what you don’t want if you’re looking for complicated multiple swing-by transfers.

Also, KSP strictly uses two-body gravity calculations. If you’re not in the Jool’s sphere of influence, it has no gravitational effect on you, for example. This vastly simplifies figuring this sort of thing out. The basic principles aren’t that hard - pass behind a planet to gain energy, in front of it to lose energy. Make inclination changes by passing slightly above or below the planet’s orbital plane.

If you want to play around with this sort of thing, bouncing around among Jool’s moons is the way to go as you get waaaaay more encounters. It’s pretty hard to make a complete elliptical orbit of Jool crossing the orbits of the three inner moons without encountering at least one of them. Only problem is that you are likely to run into one of KSP’s most persistent bugs, which will not show encounters with outer satellites if you have an upcoming encounter with an inner satellite.

I take it that Mechjeb is something connected with Kerbal Space Program? Who or what is Scott Manley?

Mechjeb is a KSP add-on that provides all manner of calculations and automation, up to and including plotting and executing maneuvers.

Scott Manley is a Youtuber well-known in the KSP community. He will fairly routinely say things like, “Oh I’ll just eyeball this one,” only to perfectly execute some rather difficult maneuver.