ORIGINAL: Evrett
So I designed a star base (research based) but it wont show up in the build options at all of my planets (or construction ship) Any idea what I'm missing ?
Here's what I found based on my own experimentation:
Spaceports can only be built at one of your colonies. Someone above said they could only be built at planets, but I found I could only build them at *colonized* planets that belong to me. Since the colony builds the Spaceport, you don't have to use a Construction ship, although you can use one if you want at small colonies since it can be faster. Spaceports can be refitted, and they don't have a maximum size. You can throw a Mining and/or Luxury Extractor on and it will increase the colony's mining rate, if it isn't already maxed.
Star Bases are different in that they can be built anywhere, even in deep space. You can even build one at colony that already has a Spaceport. Unfortunate, they can't be refitted, even when built at a colony, so it's best not to use them at colonies. This also means it's best to keep your Star Base designs within your Maximum Base Size limit.
In systems with a Spaceport or Star Base, the AI for the freighters will automatically use smaller freighters to move resources from the nearby mining stations to the Spaceport/Star Base. Larger freighters will then move needed resources to other systems. If a system doesn't have a Spaceport/Star Base, then the various mining stations must be served individually, which is much less efficient. So, you want to have a Spaceport in every system that has one or more colonies in it.
Ok, so what about when you start mining one or more systems that's far away from the nearest Spaceport and there are no colonizable planets in sight? That's where a Star Base can be handy. Have a Constructor build one around the planet with the most valuable resources, give it mining, gas, and/or luxury extraction modules, and it'll mine that planet for you too. A Construction Yard and Weapon, Energy, and HighTech Plants are optional.
A Star Base is also a good option when you want a full-service station out in the middle of nowhere at a Caslon or Hydrogen nebula. It can be a better option than simply building a well-armed Gas Mining Station. If it's really far out, throwing on a Construction Yard and a Weapon, Energy, and HighTech Plant will allow ships to repair without having to travel all the way back to the nearest Spaceport. A lot of pirate bases located in a nebula use this model.
The freighter AI may see a Star Base between two Spaceports that are too far apart as a place where it can drop goods off and let another freighter pick them up, but I haven't been able to test that. It's more likely that it'll simply refuel and keep going.