# Space station stable population

An isolated space station that has 18 lab grown babies every day. The average lifespan is 120 years. What is the total size of the population for the birth death rate ratio to be even? Im having a hard time figuring this out and Im trying to design the station around the population. If Im postimg in the wrong area please tell me where I should ask instead.

This is a relatively simple math problem.

18 people/day x 365 day/year x 120 years = 788,400 people.

This is assuming that every single person born lives for exactly 120 years. Realistically, there would be some variance (e.g. some people may die very young due to accident or disease, some people might live significantly longer), but this is still a good estimate. There will probably not be a significant difference between a society with a population of 787,000 and one with 790,000.

This is also assuming that none of the people reproduce - perhaps all the children are the same sex? If members of the population are capable of sexual reproduction, then they will reproduce. In this case, the population will grow logistically (exponentially if resources are unlimited) until they level out at an amount based on how many resources are available.

• @Fred yes it does, as after 120 years that will be the total population and an equal number of births and deaths will occur each day (on average). Jul 6, 2021 at 8:12
• Thank you. Thats what my calculator said but I wanted to double check. They are all infertile. Thats why they clone. Both genders more or less equal ratio. Jul 6, 2021 at 8:23
• +1 for the "some variance" paragraph. Jul 6, 2021 at 12:26
• Unlimited resources will not lead to an exponential growth of the population on a space station if the species are human-like. The malthusian theory does not work for post-industrial societies with high levels of education. Jul 6, 2021 at 19:01
• @Otkin That is a good point. It is true that many developed nations now have a R < 1 or are expected to in the near future. Historically, however, human population has grown exponentially when resources are plentiful. I'm not sure yet how long this recent trend will last. Some of the causes of reduced fertility rates seem to be scarcity-related (education/housing/medical costs and availability of time to be spent not at work are factors cited by the NCBI), so the trend might not occur in a truly post-scarcity society. Jul 7, 2021 at 7:50