So, here's the situation:

-The PCs are on a ship they were stowing away upon.

-They overpowered the crew.

-They checked the navicomputer and interrogated one of the crew, and realized they were in hyperspace to an enemy fleet.

The question is, can you start plotting a new hyperspace route while still in hyperspace? They want to be able to flee as quickly as possible, and have about 40 minutes before dropping out of hyperspace in the middle of a bunch of enemies.

My thoughts:

1. There are probably some holoNet updates (interstellar 'weather' among them) that are probably needed for the calculations. Not having those calculations should probably add a difficulty die.

2. However, the base algorithms that predict planet/star/other collideable object movement ARE probably stored in the computer, so I think it is POSSIBLE to try to do it.

I'm curious to see what other people think on the matter.

It's doable, at least there's a Rebels episode where they do it. Kanan asks if it's possible (suggesting he knows the possibility at least exists), and Hera responds hesitantly that she can. Hera's response could be read a number of ways. Perhaps she just didn't want to reveal the information to the crew. Perhaps it's only because the Ghost has special equipment. Perhaps it's just dangerous to do.

Personally I'd go with a Daunting or even Formidable Astrogation check, with upgrades. Failure could mean "not quite ending up where you expected", or ending up somewhere dangerous that has its own complications. Threat could be Strain damage to the ship. Despair could be damage to the hyperdrive or some other component.

Despite the fine example from Rebels given above, I have not allowed it in my games as it's just not possible to gather the required location/destination information to make the jump while traveling through hyperspace. They can always drop out of hyperspace early (likely in deep space far from anything) and calculate a new destination. This is just my house rule, so go with what you like but just try to stay consistent.

Wording is quite important here. Can you plot a new hyperspace route while in hyper space? No. The astrogation calculations are made based on using points of reference (Objects with sufficient planetary mass) to plot a course. (One of the reasons why interdictors use gravity well generators is that suddenly adding planetary mass not only prevents you from going to lightspeed it messes up all your calculations) now these are calculations based on a planetary system scale so moving at sublight scale does not change your points of refrence. However if your already IN hyperspace you move so fast you cannot establish a point of origin to start your calculations from.

In quite a number of the books its described how they use small jumps in diffrent directions to shake pursuers, if you could easily change your heading while in hyperspace there would be no need to do this. But you do have the option to drop out of hyperspace prematurely and then replot a course. The dangers of making essentially a blind jump (randomly activating your hyper drive and going wherever your ship was turned) are detailed quite well and you face these same issues if you drop out of hyperspace prematurely. They are: Materializing inside a planetary body where you'll pretty much be instantly crushed, Moving through the core of a Sun or a Black hole (which will incinerate you EVEN if you pass through them in hyperspace.) Or getting stranded in the void between galaxies where no objects with sufficient mass exist to plot an astrogation course as no points of reference exist.

However you COULD change your course while in hyperspace. Note that I said change a course not plot one, as you'll essentially be turning whicever way blindly and have no idea where your going. With all of the risks associated with a blind jump. In general most pilots consider this absolute suicide and it's rarely done except out of sheer desperation. Can you do it sure, should you? you'd probably have better odds of survival materializing in the middle of that fleet and trying to dodge blaster fire long enough to plot a new short course. Then drop out of hyperspace and use the tactic of a series of short jumps in diffrent headings that i described earlier to shake a pursuer.

This is one of those things where at least in my game I diverge a little from the new cannon. Back in the "bad old days," hyperspace was a straight line from point A to point B, where even traveling along well traveled trade route required you to revert to sublight, plot a course correction when you need to dog leg a nebula, jump to light speed and rinse/repeat. Now, if you find yourself on a rocket sled to the enemy fleet, either you aren't on the last leg, in which case you just have to wait until the leg of the trip you are on completes and hope people aren't waiting for you, or if you are on the last leg and/or really don't want to end up wherever you are heading, there are a couple of ways to pull the "emergency stop" cord.

Option 1) Just tell the navcomputer you are having an emergency and disengage the hyperdrive. Shutting it down prematurely will run the risk of damage, but it's gotta be better than showing up in the middle of an enemy fleet and trying to "NOPE" your way out, right? The problem with this solution is there is probably some kind of command override in place with a password or a biometric scanner, or you get the idea to prevent someone from just pulling the plug for funsies. Probably a computer check to bypass the security.

Option 2) Hyperdrives have safety mechanisms that shut them down when they detect a significant mass shadow in their path. This is why pirates tug big rocks into trade lanes and Interdictors have gravity well generators. Because that will automatically trigger a ship reverting to realspace and until they can get around the rock or the Interdictor, they aren't going anywhere fast. Now, actually arranging someone to get ahead of you and do this may not be possible in hyperspace, but you might be able to trick the sensor. Again, probably a computers check, but you may be able to macguyver something with mechanics to trick the sensors.

Option 3) "Sabotage" the hyperdrive. While options 1 and 2 run the risk of damaging the hyperdrive, there is no risk here. It's a certainty! The trick is finding a way to break the hyperdrive in such a way it's easy to fix (hopefully) and you don't trigger some kind of cascade failure that leaves you in a much worse lurch than you are currently in. But this is why ships have back up hyperdrives, right? Just in case?

Now, once you have dropped out of hyperspace early, if you -really- want to turn the screws as it were (and to borrow a little from the movie Stargate) it may take 6 points to define a destination, but you can't plot a course without a point of origin. If your navigational computer isn't absolutely sure of where you are, it may take it a while to rebuild a pulsar map ( http://www.pulsarmap.com/- a cheeky and easy to understand explanation of pulsar maps and why they are so cool for navigating a galaxy) to for sure know where it is so it can validate jump coordinates.

Anyway, just my thoughts on the matter. Hope it helps or gives you ideas!

WEG had the N-CRAB, I believe it was called, a prototypic contraption to plug into your navcom for just that purpose.

But, just as above poster pointed out, you can always pull the emergency break; 40 min should translate to more than 100 ly distance from the original destination.