Let's think some more about D&D Moons of Jupiter. Let's also establish none of this is based in physics or actual astronomical reality. We're dealing in broad brush strokes.
This is what I am christening a Ring Map. I've arranged the moons of Jupiter into sections of rings. (Not actually related much to their real orbits.) The way it works is as follows.
Every d6 days the innermost ring rotates one section clockwise. (The irregularity is to do with fluidity of the phlogiston, direction of Jovian Winds, etc.) Every 2d6 days, the second ring rotates one section clockwise. Every 3d6 days, the third ring rotates... And so forth. This is not difficult to keep track of - you just make the rolls at the start of the campaign for all the rings, keep a tally of days, and reroll for a given ring on the predetermined rotation date.
Ships are limited in how far they can travel. Ordinary ships can move only as far as the next moon over in any direction before needing to resupply (or running out of aether or whatever). Very expensive, fancy ships can move two. Sailing between moons takes d3 days.
So, for example, imagine the PCs are on Euporie. They want to get to Adrastea because on that rock lives a medusa who owns a magical amethyst which can cure lycanthropy or whatever. They can get there by hopping to Leda, then Europa, and then Adrastea. Each time they have to stop to resupply and each journey risks an encounter with pirates, dragons, slaad raiders, floathing aboleths, Jovian krakens, plogiston sorcerors, and so forth.
On the other hand, imagine the PCs are on Europa. They need to get to Carpo, because they've heard their enemy, the spinagon Malakofrex, is building a fortress there. They could hop from Europa to Carpo, which would take a number of 'moves'. Or they could simply wait until Europa's orbit catches up with Carpo's and make the move in one easy step - perhaps taking the time in between to research Malakofrex's weaknesses and prepare.
Needs more work: the moons which are just code numbers need Greek sounding names, and maybe some empty spaces would be good to make travel in some regions riskier. But serves as a sort of proof of concept.