Alternately, learn to upload people. Which is still probably going to require nanotech. This way, you’re not dependent on ecosystems because you don’t need anything organic. You can also modify computers to be resistant to radiation more easily than you can people.
If we can’t thrive on a wrecked Earth, the stars aren’t for us.
Kind of reminds me of a discussion of making a utilitarian emblem on felicifia.org. We never really settled on anything, but I think the best one was Σ☺.