Mistaking an asteroid for a nuke
Hope this wasn't already posted here, but apparently space command defense authorities are starting some planning to avert the catastrophy resulting from mistaking a couple hundred meter asteroid hit for a nuclear attack. Given the current geopolitical situation, a country could launch a retaliatory strike against a perceived enemy that would in fact be a 1st strike. And so on...
Jay Manifold, Rand Simberg and Glen Reynolds have been commenting on this issue on their blogs.
-p