The FHQ is not implemented, and should not be built. We may pull it from the game until it is ready.

Normally combat involves only the ships at the particular orbital location. What the FHQ did was let -all- your ships in the system join the fight, even if they weren't there. So if you had 50 battleships each at four planets, and somebody flies in with 90 battleships thinking they can beat your 50 at one planet, in fact they would be taking damage from all 200 but they could only shoot back at the 50 that were in orbit with them. It let all your ships fight as one fleet wherever they were needed.

It was impossible to do under the old combat system, and was incredibly complex under the new one, which has problems of it's own, so time just ran out before I could get back to it.