Could you use Traveller RPG rules to play Star Wars?
Could you use Traveller RPG rules to play the Star Frontiers setting?
How about Star Trek, could you do that with Traveller?
Could you do the Expanse with Traveller?
How about Larry Niven's Ringworld/Known Space setting?
Can you do Isaac Asimov's Foundation or Robots setting with Traveller?
Star Wars: Yes, was very unsatisfying.
Star Frontiers: Kind of... back when I wanted to, I was really into simulationism, and CT wasn't detailed enough to to the job I wanted; by the time Mega gave me the rules, I no longer wanted to do the Frontier in Traveller.
Star Trek - done with CT Bk5 plus AM drives backported from MT. APAWs as phasers. Was VERY unsatisfying, especially since FASA-Trek had better ship combat, and players weren't unsatisfied by random positions in the crew.
Ringworld/Known Space: either you make monomolecular shells low TL, and ships are immune to hull damage, but can be stripped of sensors and drive controls, or you run the TL way up and no longer have the right weapons...
The CoDo-verse, however... (Niven & Pournelle) Yes. Just reskin the rules for Black Globes, and take away the invisibility.
Foundation is baked into Traveller's blood. I was shocked how much of the Foundation Radioplay was represented in CT... and, for that matter, MT.
Fundamentally, the question shouldn't be «Can one do ___ in Traveller?» but «Is Traveller a good fit for ___, or is something else better?»
And also, for a homebrew conversion, «
Is it worth my time to alter something when there's an already altered game out there?»
I have done a few crossovers that weren't horrible. My Tron based adventure was a mixed success. My port of the OTU into 2300 was actually a lot of fun. My use of the Twilight 2000 2.0 engine (given the Survival Margin conversion) was far more fun for me and my players than T:TNE... (which was 2.2 based.)
I did a GURPS traveller game based upon the fan version on SJG's internet BBS... right after GT was announced, and before Loren's version was printed. And ran into the issue that Zhodani Teleport Troops are over 1000 points... or are much shorter ranged than the CT, MT, or TNE versions.
Different assumptions. Incompatible assumptions...
T20 was actually a lot of fun... but I still preferred MT to it.
I loved Mongoose Playtest draft 3.2... best rules I've run for ship combat and ship operations yet. Too bad Thrash convinced them to drop the rolling rather than fix it. Fix wasn't even hard.