I thought of something, for sending probes to the outer planets, like for orbiting them, that's planets Uranus, Neptune and Pluto. That can of course also be for going to Neptune's moon Triton. I would have mentioned it in the Uranus Orbiter? thread, but it was closed for comments.
With current technology of rockets and probes, these need to have large retro-boosters attached to them. That's because of those planets being so distant. Planet Uranus for instance is about seven times further from the sun than planet Jupiter, and planet Neptune about twice as far as planet Uranus. So, when approaching the destination, the retro-boosters fire, in order to slow it down into orbit, and falling down into the planet. The retro-boosters then detaching. The probes could also have coverings over them, with the boosters attached to those. When the boosters detach, the coverings also do.
When the Horizons probe went to planet Pluto it was going too fast to go into orbit, so just did a flyby, and it still took nine years. So, having wanted it to be going slow to go into orbit, probably would have taken about 24 years - way too long. Hence, those booster rockets for such orbital probes.