This should have been posted earlier but didnt go through for some reason. Here it is again.
As the double modules can be considered broader subjects, I figured they would be more useful in the RP as you could use it in a wider range of situations.
Stellar cartography would be to do with mapping of systems and the details of how that information is gathered, whereas astro-navigation would be to with actual navigation and moving through space such as finding the best route or simply flying a ship. The modules set out and rules laid out are only a guide and can be tweaked if something doesnt quite make sense.
I will work on adding more detailed descriptions of each module. Hopefully this will clarify them and give ideas about what they might be useful for. In doing so I might remove a couple or change them. Your character design at the moment doesnt need to be set in stone (and wont need to be as we get going either). There will be an element of trial ad improvement as we go along.
Hopefully the first scenario that I have been thinking on will give it a good test (and will be a test of my own GM skill to say the least!)