It's simple for the position you are playing in Pirates of Drinax as they have the navigator/sensor operator station.
The core book Crew Requirement section lists a navigator as a minimum. Merchant vessels and scouts allow anyone to pick up Sensors so the position is a bit casual while a Navy career focuses on Crew assignment to receive the Skill and Advanced Education to specialize in Astrogation. Checking out High Guard - Crewman, it's the same deal. That said, there can be Sensor Op crewmen galore but the Astrogator is a specially skilled person who will more than likely have Sensors as part of their package. Now, looking at the Command Section for Crew compliment, they mention Computer Officers, Navigation Officers and Communication Officers. I wish they actually describer their actual functions. The Computer Officer is the iffiest even with Traveller computers. Since the Navy likes to compartmentalize functions and stations as ships and crews get bigger, I'd say on larger vessels, the Navigator concentrates on navigation, Jump and intersystem, while a Computer Officer is also the Sensor crew. Smaller vessels with limitations on crew will combine the navigator and sensor functions.
As said earlier, other positions can have the sensor skill but don't concentrate on the combat functions without taking penalties for Multiple Actions.