>they are too fragile to serve as humanity’s “back-up”. As theme parks or transit vessels, sure. But not as our back-up.
I think this is correct. In fact, where we live now, on a (big) planet, should be our "backup" in that you can have subterranean arcologies that protect you while your habitats are blasted by gamma ray bursts, supernovae, or what have you.
(I stress big because I think we need Earth's gravity; I don't think you could lead a healthy life on Mars or much less the Moon.)
But what makes planets terrible for being your "main space" is that the climates and biology are harder to control (climate change, zoonotic pandemics, volcanos, earthquakes, tsunamis, etc.), resources are harder to get (they're buried deep while a wealth of exposed ore exists in the inner Asteroid Belt and a wealth of exposed ice exists in the outer Kuiper Belt), and as someone else here said the space is ironically much smaller than what you could have in a space habitat by surface area or open volume. The gravity's free -- you don't have to spin like you would on a habitat, but you pay for that by the fact that it's very hard to leave. You need to use half your fuel just to reach parking orbit, and it's untenable to build a space elevator. (A space fountain[0] might be doable, but it's still an ordeal.) It only becomes tenable when the gravity's much lower, but then we'll probably run into physiological problems.
I think this is correct. In fact, where we live now, on a (big) planet, should be our "backup" in that you can have subterranean arcologies that protect you while your habitats are blasted by gamma ray bursts, supernovae, or what have you. (I stress big because I think we need Earth's gravity; I don't think you could lead a healthy life on Mars or much less the Moon.)
But what makes planets terrible for being your "main space" is that the climates and biology are harder to control (climate change, zoonotic pandemics, volcanos, earthquakes, tsunamis, etc.), resources are harder to get (they're buried deep while a wealth of exposed ore exists in the inner Asteroid Belt and a wealth of exposed ice exists in the outer Kuiper Belt), and as someone else here said the space is ironically much smaller than what you could have in a space habitat by surface area or open volume. The gravity's free -- you don't have to spin like you would on a habitat, but you pay for that by the fact that it's very hard to leave. You need to use half your fuel just to reach parking orbit, and it's untenable to build a space elevator. (A space fountain[0] might be doable, but it's still an ordeal.) It only becomes tenable when the gravity's much lower, but then we'll probably run into physiological problems.
0: https://en.wikipedia.org/wiki/Space_fountain