Thruster

The thruster is an important part of your ship. It allows your ship to move faster, which can be useful to dodge enemie's Ion Cannons or cannons. Since they are 2 by 2 only, you can do this with thrusters:

It will be even better if you place walls inside of them, so your ship will have more health.

Upgrading
If you upgrade it, it will just have more health, and not get any faster.