You assume we would be able to organize the social, political, and financial impetus to take on a task like that in a unified way that has a chance to succeed.

You assume we would be able to organize the social, political, and financial impetus to take on a task like that in a unified way that has a chance to succeed. Recent events seem to say that we are at least as likely to just fight about it until the asteroid hits. For greatest success I think there would need to be two but probably not many more than two major efforts going on simulatneously, in much the same way that CMS and ATLAS experiments at CERN were independently looking for the Higgs. If one fails for some unforseen technical reason, the other might not if they took a different approach.