We have quite a diversity of defenses prepared for you and the race you decide to choose for this journey through the Cosmos.
You can build turrets, orbitals, drones, interceptors, and missiles.
The first layer of preemptive attack are the missiles, they can reach settlements and destroy enemy fleets, seamlessly, Interceptors, in the other hand, can intercept incoming fleets at short/medium distances.
Once the attack is upon your planet, the planetary orbitals kick in to protect you, followed by the drones and finally the last line of defense will be your turrets.
Good luck defending your settlements Cosmo Crafters. Keep'em safe and sound.