I've discussed a couple of alternate campaign frames previously, covering the Mercenary campaign along with the Squadron and Active Duty campaign frames. Though the last was only presented in terms of Navy games (and so incorporating Marines by default), it would have been easily converted for use with other active duty military games involving the Army. I'm going to start skipping around, because the other campaign frames from the classic Traveller era are either minor and not well detailed, or ones that I am not very familiar with at this time (I will be discussing the frame implied in The Traveller Adventure later on, which is related to the "default" Traveller campaign frame that I've also described previously, but includes some new concepts that are very important).
EDIT: Re-reading some of the World Builder's Handbook, I see that it includes more detail toward an exploration and contact game than I remembered. I may return to that supplement later.
The supplement didn't stop there, though. The other side of the Scout coin in SF is colonization, and World Tamer's Handbook presented a campaign frame of colonists, a first in SF gaming generally, and for Traveller specifically. A model was provided that allowed players to determine the economic output of their colony based on decisions they made about allocating resources both infrastructure- and human-related, which they could then direct toward various improvements and maintenance - a true domain-level game at last. This also saw the return of the sandbox format for a Traveller campaign, which had largely dropped by the wayside during the late Traveller and most of the MegaTraveller eras in favor of the then-popular story-based format. In addition to whatever the Referee chose to throw at them to further the story, colonial administrators (the PCs, the rules assume) would experience various random events that provided story hooks related to administering a group of people in a colony. Sadly, this wasn't well implemented, as the events mostly were defined in terms of a single task roll to resolve them ("Crime Wave, succeed in a Difficult Investigation roll" or suffer some penalty, for example). Nonetheless, this was a great idea, but didn't see much support from the community of players, something that can really be said about most of Traveller: The New Era, unfortunately. Some general notes toward scaling the colonial model up to cover entire world governments were included, but the system becomes unwieldy at the higher end. This would lead to a different system for world-spanning empires later on, and I will probably discuss that campaign frame next time.
designer's notes for that supplement, available for free on the SJG site, give more detail still toward a game using 3D star maps, including discussion of possible changes to the Jump Drive and so on. I should add at this point that if you have any interest in the GURPS Traveller line at all, you should hurry up and get the PDFs, as SJG's license to sell that edition expires at the end of this year, and they will not be renewing it. After that point, they will not be selling GT materials, not even the PDFs.