So I have managed to find people foolish enough to allow a first time GM to lead their first ever game of Rogue Trader. They are going through the first book of the Warpstorm trilogy so there is some frame work to help me out. Now I am just curious how much help or hindrance I should be to my players. Any person familiar with this game or these forums knows PCs will find impressive and some times confusing ways of solving problems, sometimes even when there is no problem to fix. As an example the parties rogue trader, arch-militant, senschel, and void master decided to attend the gala event. Their navigator and astropath, both who would have been useful to have at the party, hit upon the idea to to sneak around and rig explosive charges though out the factories in the city "just in case". Should I let them do these kind of things or caution them away from something that will likely get them caught?

That is a strange use for an Astropath and a Navigator, but RT is like that. My advice is to let them, and then just set appropriate consequences if/when they are caught. If someone sees a psyker and a mutant planting explosives in Imperial Manufactoria, that person, having been born and raised in the world of "Abhor the Witch" and "Know the Mutant, Kill the Mutant" is about 50/50 to either attack them with a wrench or scream very loudly. And Emperor help them if the Arbites hears about that. There could also be investigations when some whirring servo-skull inevitably finds and flags them, though in that case the players should have ample time to quietly board their ship and get outta dodge, as no one would have the power to simply arrest the Rogue Trader's senior officers without a great deal of evidence. However, whatever you do, do not make them feel like they are simply being punished for having off-the-wall ideas. I've seen some weird things in RT, and quite frankly in my opinion it should be no other way. Just don't be dropping the NO-hammer on them for their weird ideas is what i'm trying to say through that rambling nonsense, just be prepared to give consequences. (of course, be prepared to reward them as well)

So the two most conspicuous members of the crew, typically the ones least talented in demolitions, decide to sneak around and place remote explosives in the factories of a city that's about to go to war with Orks.

Death by stupidity is never the GM's fault; let them try to place a few explosives, have guards catch on to it and try to capture or kill the 'terrorist Ork sypathisers' or 'Ork Kommandos masquerading as foul abhuman monsters', drag them before the governor in the middle of the gala. Both characters now have to explain what they were thinking. RT then gets to try and salvage the situation and hopefully embarrass the characters into behaving in the future.

I generally find it's handy to ask players why they want to do something, if it's abundantly stupid. Oftentimes they'll latch onto something you've mentioned and forgot about, and work up a huge theory of what they should do based on that. Having them explain their logic can allow you to go "Oh, no, you've misunderstood. What I meant by that was x;it's pretty common knowledge that y, so your character probably wouldn't want to z."

I don't see why they should necessarily get caught. Impose appropriate (and perhaps parallel or alternate) opportunities for silent move, concealment, deceive, etc. type tests (Telepathy on the Astropath would obviously represent a tremendous boon to their efforts here). If they plan it properly or luck out, then good for them. If things work out poorly then they'll have some rather unfortunate consequences. It should be a difficult and risky affair, but discovery and failure shouldn't be a foregone conclusion just because it isn't the best idea in the world. Their rolls and tactical decisions should be the final determinant of that. Even an Astropath and a Navigator can wrap themselves in rags or heavy industrial suits and there many possible uses of psychic powers that could help decrease the peril of their course of action.

In a straightforward situation like this, I'd be happy to allow it. If they can figure out a workable plan, good for them. Their characters ought to be aware of their limitations, however, and if they *are* terrible at sneaking and demolitions (which isn't necessarily the case), and the areas in question are under heavy guard, the odds should not favour them. Let them roll their stealth, and let the guards roll their awareness, and see where it goes from there. Personally, I think this is a wonderful idea and could lead to lots of cool chase scene shenanigans and stuff.

The number one thing I would advise against is making them fail by GM fiat unless what they're doing is literally impossible. Removing the players' agency is the very definition of railroading.

On the other hand, while it has nothing to do with this specific situation, I personally have put a complete ban on technobabble and plot devices. If you happen to sneak into a hive and blow up their void shield generators, that's fine. If you want to hack into someone's cogitator core and drain their information, that's also fine. If you want to tailor a gas bomb that will target the DNA of a specific dynasty, forget it. Likewise, if you want to jury-rig your plasma drive to emit an EMP to disable the invading Mechanicus forces, that is also not going to happen. You may not create win-buttons out of thin air.

Well their plan had some decent reasoning behind it, the navigator has peer(AdMech) and an interest in archeotech. She figured that distracting any tech priests with an archeotech laspistol and letting them play with it could distract them long enough for them to plant charges as they are being given a guided tour as thanks for being able to examine the pistol. My response was to warn them it had a very high chance of going horribly wrong and suggested maybe asking the rest of the groups players about it before doing something that could potentially wreck the game on day one.

Yeah, sometimes you just don't know what is going through your players' heads, and if you play the antagonist GM you never will because the players won't trust you with their schemes. On the other hand, encouraging lunacy will derail your game.

The first thing that comes to my mind when I hear something like this is, "Why are these players breaking the party apart on a mission that will likely take up an hour or more of game time from other people when the majority of the party decided that another course of action is better? Does this have a real purpose or are the players just looking to showcase themselves?" I'm not against characters going in different directions but I do monitor the amount of time players monopolize.

Yeah, this whole set-up made me go "huh?" Are they hoping to cripple the area, in order to allow an Ork victory? (Do they even know Orks are an upcoming thing?) Are they trying to hinder an enemy? Make an opportunity for an ally? Do they just want to see a BOOM!!! Does the rest of the team know what their peers are doing?

I agree that, especially with a theme like Rogue Trader's, it is important to let the players feel that they have some decent choice in what to do, and how to go about it, but I'd balance that with making sure that they want to do it for a reason, rather than "I'm bored or uneducated in this setting, and I just want to see what what I might do will result in." The grimdark future is grimdark, and should not tolerate stupid-pointless. Players can sometimes get past this, but they should HAVE TO get past this.