There was a fun cold war movie about it .

While earth is threatened by an asteroid, Russian - USA discussions happens on cooperation to defend our planet. Rough quote:

"We all knows no one has nuclear weapons in orbit, as it is forbidden by treaty XXX

But in the hypothesis some nuclear weapons actually existed in orbit anyway... how good would they perform against an asteroid ?"

In the end, >!maybe 50 % of the nukes randomly failed before reaching the asteroid!<

Not sure of the exact movie, probably [Meteor](https://en.wikipedia.org/wiki/Meteor_(film))