Greetings to all servants of Emperor, Ruinous Powers' minions, mutants, heretics and xeno-scum.

I'm am about to start a Rogue Trader campaign for players who are mostly unfamiliar with Rogue Trader's setting. I myself am quite familiar with the Warhammer 40K world overall, just not Rogue Traders that much. The trick is that I want to run game using Fate Core system.

I saw Lure of the Expanse recommened in many places, so that probably will be the campaign I start with. Now the question becomes: What other books I could make good use of? Will the main Rogue Trader corebook be of any use if I don't plan to use the actual rules system. Would some other campaign perhaps be better and how are the signle adventures in other sourcebooks? Has anyone here used Fate or other systems for Rogue Trader?

I've considered using Fate for 40k before, specifically Rogue Trader. I have run RT with Savage Worlds once. It transferred over very well. As far as using Fate goes, yes, I think the Core book is still very useful, if only for flavor. I think you'll find the starship combat sections very appropo, as well as equipment. Mostly, you'll want the fluff descriptions of how RT Dynasties operate, though.

I'd be interested in seeing any documents you generate for the conversion. RT in particular, is especially suited for a Fate-style RPG since so many of the scenes are well-suited for narration. It's also well-suited for player input and plot-bending.

I personally don't care for Lure of the Expanse, and IMO the Fate system would only enhance my dislike for it. In short, the timing of LotE is contrived, and contrivances are generated in Fate by both the GM and the players. All the books have flavor-enhancing stuff for a Fate game, so I don't know which to recommend (I have them all). In the end, though, I'd make my own scenarios and/or campaign (I do anyway, but...) since it wouldn't be much of an imposition to come up with loads of stuff since you aren't having to spend so much time on the minutae of NPC attributes, skills, etc., and rules/systems.

I have no idea on what Fate Core is; however, if you have a new group, and want to play WH40k, then I recommend to simply play WH40k. The core book has allot of fluff and info for anyone new to the setting to get a feel for it. Implementing a different book for a core setting is just going to confuse new players, from my experience. If you want the rules from Fate Core for your game, then be up front with your players and explain that. But if both systems are new to your players, then use the Kiss method (keep it simple silly). Best of luck to you no matter what though.

As Errant said, the CRB is good for the information it has on who and what a Rogue Trader is and what they do, as well as the information on the Koronus Expanse and Footfall. In total, about a third of the book. Other sections can still be useful for getting a feel of what's appropriate for characters and personalities in this setting - the Origins can provide ideas, as can the page-long descriptions of each career. Even the Armory could prove useful from reading the descriptions of the weapons (rather then the stat-chart).

Into the Storm could also prove useful, as it's essentially an expansion CRB, but probably isn't the most economically efficient. Still, things like Ship Roles, expanded armory, alternate career ideas and the information on Port Wander could prove useful.

Koronus Bestiary and Stars of Inequity are both good GM tool that are much more description than stats, the first being your Monsters the latter your world building.

The adventure modules (GM kit, Lure of the Expanse, Frozen Reaches, Citadel of Skulls, Fallen Suns) are, well, adventure modules - so their utility depends on if you like those kinds of things. Personally, I find myself doing a lot better when I build out and on a written module (mostly because of time...) but I know people who wouldn't touch it with a 10' sanctified pole.

For Lure of the Expanse specifically, I know a lot of people who have broken it down into 3+ mini-adventures rather than run it through as presented, and honestly were I to run it again, I'd probably do the same - drop the whole race-to-the-planet aspect and use the majority of it for planet-of-the-week episodes.

Frozen Reaches is a lot of fun, but needs some scale-work to fight correctly. Dealing with the mass combat, however, could prove difficult in the Fate system, so I'd give it some consideration first. Citadel of Skulls is entertaining if nothing else, and I & my players really enjoyed Fallen Suns, but its one that could really depend on your player/character motivation and type. I'm actually really a fan of the GM kit's Whispers module, though it needs a huge amount of build out. I find it a great way to tie your RT to the expanse and form a foundation of the rest of your game.