>>12880736Phobos is ironically shaped to be perfect for a seed ship. The impact crater is nearly convex and perfect for an exhaust port for engines. It's also large enough that you can drill a hole into it on one side and excavate and carve out an internal volume to create a RAMA like environment.
Dimensions 27 × 22 × 18 km (Usable mean radius of 11.267km)
This means you create a usable volume that's 6km in diameter and 12km in length. It creates a usable volume of 1,357km^3. That's also 678km^2 surface area on the inner surface of the cylinder.
https://worldbuilding.stackexchange.com/questions/9582/how-many-people-can-you-feed-per-square-kilometer-of-farmland#:~:text=Since%20a%20square%20kilometer%20is,land%20can%20feed%20111%20people.
1km^2 can support 111 people. Phobos' inner cylinder theoretically, if you were to dedicate 25% of it to farmland, which is 169.5km^2. That would be able to support 18,814.5 people. But we know that farmlands in space will be inefficient for growing crops--but will be kept around because they're psychologically positive; it reminds us of Earth, green fields, home; etc. The 6km radius at the caps of the cylinder would likely be where much of the scientific and production facilities would be. The 2nd shell of the cylinder 1km thick can also support all the dirty (mining, refining, manufacturing) industries--keeping the inner drum pure.
So the caps would contain all the clean material facilities and mostly vertical farms. If you assume 6km for the radius and 250 meters height cap, that gives you 226km^2 of workable area. If you further assume that half on both ends will be dedicated to vertical farming for the colony, that's 226km^2 usable flatland.
According to this source:
https://www.researchgate.net/publication/259702659_Up_Up_and_Away_The_Economics_of_Vertical_Farming | 0.25ha VF yields 516x the yield of an equivalent traditional farm.
IF 2030-40 tech + 1km^2 ref to compare, 226km --> 226 * 516 * 111 = 12.9M pop support.
