Okay. I get and agree with the perceived issue. See my options for a solution....
What I don't get is the ' I am personally hoping for a population cap mechanic for space stations, which works similarly to what we have for orbital bodies.' What mechanic is this that differentiates between the two? What mechanic solves this issue for orbital bodies? 'Stable' doesn't stop pop from making babies.
I'm not trying to be difficult Aurora constantly teaches me that I need to keep asking questions to learn what I don't know. That statement sounds like there is a mechanic to stop pop from growing on orbital bodies that I am unaware of.
Is the difference one of having habs around a body but no colony on the body? Makes me curious as to when that is a reasonable action. What is the point of habs if there is no colony housing installations that need workers?
An orbital habitat adds orbital habitation capacity to a planet
on top of whatever population capacity the planet has - this means that workers living in habitats will work installations on the surface, hence why there aren't any "ship" component that need workers. More importantly, orbital habitats provide population capacity that is independent of the colony cost of the world in question. This means for planets like Venus it is easier and cheaper to use orbital habitats instead of infrastructure.
Another important point is how workers are distributed in a planetary work force. There are three sectors; agricultural, service and manufacturing. Service isn't too important for this discussion but it starts at 0% and goes to 70% max as the colony grows in size. Agriculture takes a minimum of 5% of the workforce and for every 1 CC it takes an additional 5% (might be wrong on the specific number but you get the gist) so a colony cost 1 world will need 10% agriculture. Lastly the manufacturing sector is whatever remains - this is the workforce available to work in your factories on the surface.
The problem with high colony cost worlds is that they might need too much agricultural workers leaving no workers for a useful manufacturing sector. This is where orbital habitats come in. Population living in an orbital habitat
requires no agriculture sector, as such you can use orbital habitats on high colony cost worlds that would otherwise not provide a useable workforce.
So we finally arrive at the population growth issue that people are on about. You are absolutely correct, you can set the planet to "stable" in order to prevent colonists from being brought in but it wont stop people being born. Normally this is fine, but if you have a planet that is colonizable with infrastructure like Venus that also has orbital habitats you encounter a problem. The orbital habitation capacity is independent of the surface population capacity, so if a planet can house 2.5bn people but the orbital habitats can only fit 400m, eventually the orbital habitats will fill up and newborns on that colony will instead go on the surface and automatically build infrastructure to live there.
This causes two problems:
- Unrest starts to rise because the people who initially land on the surface die to the planet (overcrowding) since they haven't built the infrastructure yet to support living on the surface.
- Now that there are people living on the surface
the entire population needs an agricultural sector, on high CC planets like Venus this is a disaster because you will actually lose workers.
So what people are asking for is not an option to stop births in general - it's to allow someone to mark the colony as an orbital only colony - that way people do not go down on the surface automatically and ruin an otherwise viable colony.
Edit: There will always be a colony on a body regardless of whether or not there are orbital habitats present