I got sidetracked for a while, but here are some answers from that chat:

Ideally you just swap planets. Whatever you have set up for them on planet one is now surprise on planet two.

[in response to the above] This is the default solution for story focused games. The story continues to the next act, the players dictate how.

“I hadn’t thought of that! I don’t have anything prepared. Why don’t we just pause things here for now and chat. I’ll have it ready next time.”

I guess the question is how far off the path? Jump 1 away or Jump 6? GM completely unprepared? Or not as prepared as you’d like? As a Traveller GM I’ve got

• The notes for every planet and system within range of the PCs ship x2. I.e. for J2 every system within 4 parsecs.
• A list of 100+ random NPC names
• A couple sentences about each system
• Same for the two to five largest factions in my setting

So if the PCs wander I’ve usually got enough material for one night’s worth of material

An easy delay is simply to go into more detail. For example, have them go through the steps of Customs at the new starport, or notice something interesting about another ship, etc. It adds texture to the game, is interesting, and gives you the extra time to prep.

For my group (not sure if it will work for every group) i just leveraged their completionist mindsets. I told them "here are 15 jobs" and the first thing they did was plot an exact course to hit all of them, so they prevented themselves from wandering.

The last one is my favorite of this bunch, because as a player I'd fall for that hook, line, and sinker.

Thank you everyone for participating!