It'll never happen. The green misanthropes would love nothing more than to have a large rock smack the Earth and reduce to human species to "manageable levels" if not outright eradicating it. And, these environazis have enough clout with the world's governments to put the kabosh on any plans to put nuclear weapons in space.
And, these environazis have enough clout with the world's governments to put the kabosh on any plans to put nuclear weapons in space. And the problem then is...?
After the big show...
Let's just find some big rocks, deal with the weenies and start over.
Malthus is vindicated... ditto Darwin...
Everybody wins.