That seems like a problem in itself, it needs to be on a hair trigger to fire soon enough to catch a weapon soon after launch. Sure would be bad to accidentally shoot down an unannounced manned rocket launch after the software thought it was a nuclear launch.
Oh, so as long as the humans in every country that announce the rocket launches and the humans that enter known launches into missile defense systems do their jobs perfectly every single time, then everything will be ok.
this got miscommunicated once and led to Boris Yeltsin opening the nuclear football and weighing launch orders when the call came in that it was actually a Norwegian sounding rocket, not a surprise Arctic first strike.
