I've seen some technical drawings that say this dome is the "Main Navigational Sensor Array" and the one on the bottom is the "Planetary Sensor Array". Okay, how might a dome-shaped nav sensor work?? I have a theory about that. Imagine a bundle of thousands of very skinny meter-long soda straws that have a slight taper of, say, 0.05mm wider at one end than the other. When the straws are bound together, this taper will cause them to naturally form a dome. Each straw will have a tiny sensor on the narrow end, inside the dome. Ergo, the sensor can see only the light that enters directly into the other end of the straw. As each straw is pointed at an oh-so-slightly different angle than the next straw, the array can measure with pin-point accuracy the direction to each star it sees. Also, the sensor can determine the spectral signature of the stars and thus identify which stars it sees. From that data, it's simple math to triangulate the ship's location in the know galaxy. It makes sense in my head. Does it make sense to you??