Well, if I recall correctly, Nausica is a heavily polluted world, in addition to being heavily populated. Given that, along with the various other dramatic elements that you can throw in (sensor malfunctions, need for re-calibration, etc), it could be exceedingly difficult.
Obviously, you as the Narrator have to decide if you want the ship to be able to locate the PC's. If you do, do you want it to be for a dramatic escape, or just whenever the PC's (or NPC's) on the ship would be able to manage it?
For me, Trek sensors have always been a tricky thing, and they're generally something that I use for story advancement and/or drama. If the PC's come up with a good idea for sensor use, I'm never opposed to it, since stumping the Narrator is part of the players' jobs...
Greg
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