45 minutes warning
For the smaller comet fragments, what you need is about 45 minutes warning of the exact impact location. With that, you can safe the nuclear power plants, safe the industrial facilitites, shut down the natural gas supplies, safe the pipelines - and get the population into cover from the blast - even weak shelter like a basement or bathroom will do - alert your recovery teams
You only loose those few at the immediate center of the impact -
The internet docs on CAPS may be found by googling CAPS and Mazanek, who was the team leader. But to get what's publicly available of the study you'd have to contact the Langley PAO.