In most cases of “conventional” xrisks (< 10km diameter impactors, (current tech) wars, famine, super volcanoes, (nearly all) climate change scenarios, global computer failure, most pandemics (sub 100% lethality), most supernova scenarios) you don’t even need the shelter.
It is sufficient to have the tech necessary to be self sufficient in a small (say 1000 people) group independently from ecosystem services (i.e. food, water, maybe air—not an issue in most scenarios, organic raw materials, fossil fuels). This is the minimum requirement for a martian colony or a deep shelter anyway and much easier, especially if you use outside air. Though it is still very hard—today we don’t come close to be independent form ecosystem services even with a supply chain of 7 billion people. I doubt it is possible at all short of some sort of MNT.
As long as we are not independent form ecosystem services in a small group a space- or underground- or oceanic colony as protection from xrisks is a pipe dream, because any settlement not completely independent from the mother civilisation will die long before the mother civilisation breaks down. Especially if transport is as demanding as to Mars.
In most cases of “conventional” xrisks (< 10km diameter impactors, (current tech) wars, famine, super volcanoes, (nearly all) climate change scenarios, global computer failure, most pandemics (sub 100% lethality), most supernova scenarios) you don’t even need the shelter.
It is sufficient to have the tech necessary to be self sufficient in a small (say 1000 people) group independently from ecosystem services (i.e. food, water, maybe air—not an issue in most scenarios, organic raw materials, fossil fuels). This is the minimum requirement for a martian colony or a deep shelter anyway and much easier, especially if you use outside air. Though it is still very hard—today we don’t come close to be independent form ecosystem services even with a supply chain of 7 billion people. I doubt it is possible at all short of some sort of MNT.
As long as we are not independent form ecosystem services in a small group a space- or underground- or oceanic colony as protection from xrisks is a pipe dream, because any settlement not completely independent from the mother civilisation will die long before the mother civilisation breaks down. Especially if transport is as demanding as to Mars.