User Monomyth posed an interesting question on the Traveller discord that I wanted to replicate here:
hi team, just a quick discussion based question with no right answer; if youre running a game, and the players decide to veer off course into something completely out of left field (such as going to a planet you do not have prepped), is it appropriate to come up with some "delaying issue" so you can have it ready for next session?
Transposing to other settings: what do you do when the players go off-script?
I can summarize some answers we’ve got on that server, but I don’t want to prime your answers from the start.
Zozer Games has a few solo Traveller books that are well regarded.
There's one aptly named Solo for general traveller adventures, there's Hostile Solo for an Alien / Aliens feel and some really cool squad mechanics. I think there's a third supplement, but I'm not sure.
Edit: aha! The third book! Classic Traveller style, I'm guessing by the price there's minimal artwork.