An indispensable device which gives you a 360 degree view of your immediate surroundings, allowing you to know where your enemies are even when they are out of view.
Not a necessary device, but a good one. You get quite a bit of money from a single tonne of cargo space. You do get some information about your opponent, but it rarely changes your fighting strategy.
A must have for small/medium ships that can't withstand many missile hits. The naval one is preferred, but a bit expensive. Large ships with a lot of shields can survive a few missiles and don't need it.
Before damaging your ship, enemy shots have to go through your shields. This means you'll have to take significant damage before you lose vital equipment like your autopilot. Having a lot of them is nice, but remember you are not indestructable. Occasionally an opponent with a 20MW beam laser will show up and kill you no matter how many shields you have.