A number of years ago - just a bit longer than a generation - a number of independent companies began the privately funded colonization of the Arucanis Arm. This remote section of space is believed to contain a number of species and civilizations that the Federation has yet to contact. Needless to say, the Federation government was alarmed but at the time its leaders decided to respect the right of the colonists, who were mostly humans but with a few members of other Federation species, to self determination.
But war does strange things to people, and the war with the Klingons has gone on longer than any in the Federation expected. The current stalemate as well as rumors that the Klingon empire is seeking an alliance with the Romulans have made the Federation council desperate. They have begun seeking their own allies in unlikely places, and a number of council members believe that it is time someone investigate the situation in the Arucanis Arm.
The Arm lies in an extremely strategically important are where the initial Klingon advance at the beginning of the war managed to create a sliver of Klingon occupied space between the Federation and the semi-independent colonies. If the colonies and unknown civilizations of the Arm could be convinced to join the Federation in the war, the Klingons' main supply lines to the front would be severed.
You are the crew of the USS Reliant and your mission is to survey the systems Arucanis Arm, make contact with the colonists as well as the unknown species, and convince them to join the war against the Klingons. The Reliant is a New Light Cruiser, a wartime design that provides a not inconsiderable amount of firepower at a relatively low cost. Unfortunately, this is possible due to the fact that much of the crew amenities have been stripped out, and thus this assignment is more spartan than a Federation exploration or battle cruiser. However, the Reliant was chosen for a very specific reason: the common nature of its class will mean that the Klingons are less alarmed by its crossing their borders into the Arucanis Arm. The Federation feels that any other ship would likely tip the Klingons off to the purpose of the mission, and thus endanger it.
Starfleet has made contact with the company that settled the closest section of the arm, now a small merchant empire headed by one Harcourt Fenton Mudd, a criminal from Federation space and fairly recent arrival to the Arm. How he came to be in charge of the company is as yet a mystery, but he has agreed to help the Federation in exchange for amnesty and possible asylum at some future point. The aid he is willing to provide at this point does not include fighting men or ships, but his company can offer their space stations to the Reliant for refueling and shore leave. Mudd is also adamant that Starfleet inform you that he has quite a few suggestions for the latter purpose.
This posts premise and title is taken from the somewhat obscure game Protostar: War on the Frontier, which the internet consistently tells me is mediocre at best. However, I thought it had a good setup for a game that would be easily adaptable for settings of most any genre, though sci fi is obviously the easiest for it to port to. I have expressed it in terms of Star Trek rather than Traveller partly because I think those terms are more broadly familiar, and partly because I've had a deep desire to run Star Trek that coincides with, and to some degree predates, my recent Traveller mania.
If I were to keep it Trek, I'd almost certainly borrow from a number of "non-canon" sources including the material for Star Trek Phase II (the unaired series, not the fan series with the same name), the closely related Star Fleet Universe (including that ship design up there), FASA's Star Trek supplements, and the animated series. I'm not sure what system I'd use. The two options that I would be most likely to look at are a kitbashed Traveller converted for Star Trek shenanigans or FASA Trek itself. The first has some advantages, namely that I know I like the system and I have a bunch of red, blue, and yellow d6s, but it would probably take the most work. Having looked at FASA Trek recently I see a lot to like there, but I'd probably have to houserule the combat into basically being regular old BRP combat before I'd use it.
I could also use part of the Terran Directorate setting, exchanging the Klingons for [Click], but there are a number of adventure ideas I can think of for this that would work better with Star Fleet do-gooders.