Spaceports are required to allow resource (minerals, organics, radioactives, research and intelligence) points to contribute to your empire. Only 1 spaceport per system is required, but you can make more if interested in redundancy so that an attack on the spaceport planet won't necessarily cut off the whole system. The exception to this is the Natural Merchant ability which allows you to not need any spaceports, your homeworlds will have an extra Mineral Miner Facility or Research Center in that slot. Planets in a system without a spaceport are marked with a red spaceport icon, and on (F5) Colonies/Production, their output is shown in parentheses because those resources are not being added to the empire resource pool.
If a planet with a spaceport is blockaded, the resource sharing ability for the whole system still works, but no contribution of resources is made by the blockaded planet. So in this case non-blockaded planets in that system would still contribute to the general resource "pool".
If a system does not have a spaceport (or the Natural Merchant trait), no resources from that system contribute to the empire general "pool".
You can always build anything (facilities, ships, etc.) in a system even if the system does not have a spaceport. The resources used for construction will still be deducted out of the general "pool" even if there is no spaceport in the system.
It doesn't matter if a system is "cut off" from the rest of your empire; your spaceports will still work and planets will still contribute to the resource pool and that system will still be able to use resources. "Cut Off" meaning either disconnected by warp point closing or isolated by enemy systems.
| Manual (SEIV)