GURPS Prime Directive allows characters to be anything, from the bridge crew to the Marines, from diplomats to archaeologists, from a bunch of reserve officers looking to recapture the adventures of their long-lost youth, to a squadron of fighter pilots whose parties are as wild as their dogfights. Or you could be a Prime Team, Star Fleet's elite problem solving teams that combine the skills of scientists, diplomats, and commandos.
I read this ruleset awhile back. All in all it's an interesting role-playing game take on Star Trek, albeit a seriously non-canon one. It takes its basis from the Star Fleet Battles universe filtered through a bit of Franz Joseph and beefed up with a large helping of space opera-like aliens and technology. Some of it is familiar, other bits are borrowed from various SciFi tropes. It is fun stuff as long as you understand that there is a significant divergence from the TV shows and films. If you are looking for an RPG that uses GURPS rules (or D20, it is available in that flavor as well) and gives you the Star Trek vibe with out going all Kirk or Picard or even Janeway, this will fill the bill nicely.