I realize that this is a beta and that there are fewer ships/structures in this version of the game than there will be in final, but it occurs to me that a few more defensive structure options would be useful. For instance the gauss platform is decent but is only usefull in large concentrations which are easily avoided or taken out with long range ships like the LRM Frigate. Hangars are great but don't have any intrinsic defensive abilities or weapons although the fighters they launch can and will play havoc with an attack unless the attacker has sufficient anti-strikecraft units. What defenses need are a few structures or upgrades to fill in the tactical gaps between hangars and Gauss turrets. So here are some ideas:

1A longer range more powerful defensive turret would be great, maybe something like a permanent version of the Sova's missile pod.

2A command center defensive structure. Something like a giant space station with strong defensive weapons and maybe a couple squadrons that would enhance the overall performance of the defensive structures at the planet.

3This one may fit in more with one of the other races, but a spatial manipulation structure that could slow enemy ships down, interfere with their weapons or speed up and increase maneuverability of allied ships. This one could also probably be an ECM structure for some races and simply spoof enemy fire so that the enemy didn't do as much damage.

4Use the planet itself to deploy defenses, I mean the planet isn't just a waypoint, it's a giant floating tactical point in space with huge swatches of usable area that could be turned into strong defensive bonuses for the system. This would obviously have to in someway affect the planet's development, maybe make the player make a choice between military development or population development so that military development decreases the maximum number of population developments that a planet can have. You could also make planet types like Asteroids be well-suited to military development so that while an asteroid can only have 1 population development on it, it could have several military developments on it making asteroids extremely useful as defensive shield planets.