This is a very well done and polished game, for it to be taken one extra level both visually and in functionality there's two things that i'd like to suggest.
The passenger ships, when they are done with one of the extraction points they don't go automatically for the next, my recommendation is to make them go for the closest one if the one that they are currently assigned to is finished. Found them idle at the delivery zone.
The ships when they shoot don't turn, you could make them turn with an offset, and that way tou could make ships that shoot from the sides or from the front, and they wouldn't look "idle" while shooting as they swap targets and aim for them.
Cheers, solid game here! :D