So, I'm about to GM the Lure of the Expanse campaign, and one particular part of it is confusing me, namely chapter 2. The planet gazetteers have lots of info that has been previously discovered about the planets by the Imperium. The question is: How much of this do the players know? Then there's Zayth, where the players are supposed to land on a very specific land-ship to speak to a very specific crew member. How do they even know which land-ship to land at? I find that there are many situations in this adventure where it's very unclear what the GM is even supposed to let the players know or even figure out with research, and there are situations where the author seems to make grand assumptions that the players will know to do a specific thing with no indication of how this knowledge is imparted on them.

Any tips?

I would go with this :-

Whichever city thing they make actual contact with is the one they want. Have the various factions send them greetings and formal invitations to dinner / trade negotiations or whatever to make it plain that there is no unified social order and that they're dealing with the best of trade opportunities (the ones where multiple factions are looking to get their deal above everyone else). The one they accept is the one that leads to the plot hook.

As for how they know who they're talking to, the individual will introduce him or herself. Possibly a secretary or master of protocol will give them the details that the individual wants to be known with a little extra juicey gossip / lies if they make some good social rolls.

Business between people of substance is carried out face to face, in private and usually after some form of bread breaking ceremony / sharing a drink.

How this translates to the mechanicus I can't really say as they are a bunch of techno-religious lunatics.

As for how much they know about the various planets or regions of the expanse that is up to them. If they say "what do we know" then you can decide what they know. Always remember that in the grim darkness of the 41st millennium that rumor and superstition are far more common than actual fact. Their knowledge may be from the records of the previous holder of their warrant of trade, rumors and intelligence reports gathered by the seneschal's network of spies or just tavern gossip (the highest class of tavern of course).

Zyarth is pretty clear, the land ship the explorers end up on is the one which the data they find in the crashed shuttle points them to, and the individual they find is again named in the data. The data should include descriptions of both the particular landship and the person they are looking for and the position held by the man they are looking for, which when they arrive they can simply ask after. I'd lay bets that you could also monitor local vox traffic to identify different landships as well.

Finding out who and where they need to go and see is part of the adventure, it's up to the explorers to find these answers in imaginative ways, such as looking through archives to find the old imperial reports, or hacking data traffic and questioning locals.

Holes in the knowledge of the explorers is not a barrier, but a challenge they need to think to overcome.

Alternitively you can simply pass onto them anythng you think that they would know without difficulty, or anything which should be immediately obvious through observation, like the ten foot high letters emblazoned on the side of a landship should you decide that to be the case.

I always assume my players know nothing about the various worlds unless they make a relevant lore skill check. Common lore: Koronus Expanse would be highly relevant here. Maybe Forbidden Lore: Adeptus Mechanicus would let them know that the Admech have been interested in the world due to the mobile cities. Maybe a Scholastic lore: archaic or legend might reveal ancient legends about moving hive cities and fabulous hoards of archeotech buried under shifting sands.

Thanks for the replies! Some good input there that will come to good use when I start the adventure. It's just too bad that this info isn't printed in the book. It does a great job of giving you suggestions for skill use in all cases but knowledge checks, and I can't figure out why. Coming up with the correct knowledge skill to use on the fly when you're new to the system isn't really an easy task.

I found that 90% of the information in Parts 1 and 2 of Lure of the Expanse assumes the Explorers are going to go about things a certain way, which I think most groups will not do. On Footfall for example, the encounters seem to assume they will wander round with very little regard to their own security and allow small groups of semi-skilled thugs to attack them, from which they'll eventually find out enough information to move on. There really isn't anything to cover their actual legwork, and sweeping statements all over the place (I forget the wording, but essentially "By now everyone on Footfall will know what the Explorers are looking for". In my opinion the best way to manage this is relax, make up details to fill the gaps in what the book gives you, and let them do things their way - unless their way blatantly won't work.

For the planets in Part 2, I gave them the first paragraph of the description in the Main Rulebook where there was one, so they essentially knew 'war world', 'desert world', 'feral world' as well as the names. I used these as a guide to create similar descriptions for the other points based on what the scenario gave me. This was the sort of generalised information that allowed them to make distinctions between the worlds, but not necessarily enough to make a workable plan (e.g. "We'll trade for primitive jewellery on Dross and sell it to the people on Zayth" - if they knew more, they'd know that's unlikely to work). If they make Koronus Expanse Lore rolls they'd get more useful info (e.g. "Only one person has ever made it back from Dross before) that would prepare them better.