The game is a little klunky with space stations and constructors. If you send constructors to a space station you need to park them one square away so the game will prompt you that the ship is idle. If you send them directly to the space station they will go to the station and get added to "the bucket list" for that station. Then you need to periodically go through each station to find out if there are constructors that are there, just cooling their heels and not working to making improvements.
Also, with constructors, if you send them to a station and there are no more techs that you can apply (until you up your technology) the constructors will sit there, as if they are docked, there is no prompt that maybe you need to check up on things.
I also suggest adding another class of vessel. "Drones" that work within the area of influence of the station. These may be mining-bots, defense-bots, influence-bots (missionaries), (loan sharks for finance? <lol>).
Another one, when you upgrade a ship (like in deep space) it takes a certain number of turns (cost?). If your ship is within the zone of influence of a shipyard (or station) can that time/cost be decreased? Maybe for something like a shipyard, if they undertake repairs of nearby ships they can get a few more hit points? (kind of like experience gained when making an upgrade can help your own shipyard (or station).