Well I just finished building two ~50,000 ton Destroyers to act as a quick defense for Earth until I get some PDCs, and actual defense capable ships. Well it turns out I totally failed I forgot to put engines on the damned things, so they are now just chunks of Duranium with 30 Dual 15cm Laser Turrets and 6 20 CM Railguns floating around Earth
Orbital defense bases!
Started a new game today, and already thinking about another Aurora LP. Undecided if I want to do a narrative style LP, or maybe a hybrid LP/tutorial since everyone complains about the lack of an up to date one.
Edit: Does a railgun on a defense platform have a tracking speed of 0?
No it will have tracking speed equal to the tracking speed you have researched.
Which is usually a bit slower than you want, so I'd recommend putting turrets on platforms rather than built-in guns. The extra weight of a turret isn't nearly as much of an issue for a platform.
CIWS are not something any sane person would want to use. Feasible or not, they're useless.
....I use them all the damn time.
Against an enemy that fires manageable salvoes (Precursors in my main game have a slew of ships that fire 3-9 size 8 missiles in a volley) they're golden once you get the gauss ROF up to 4. Now, they get hopelessly overwhelmed by the 60-shot volleys of AMMs that the orbital platforms launch, but that's a different issue.
I find that putting 1-2 CIWS on a scout vessel drastically improves its survivability when meeting new and interesting lifeforms who decide they want to kill me.