DSP and more recently SBIRS are satellite-based systems, both use IR. If you tra...

DSP and more recently SBIRS are satellite-based systems, both use IR. If you track the missile to the end of it's burn you'll have a pretty good idea of where it's going after that -- ballistic trajectories are fairly predictable.

https://en.wikipedia.org/wiki/Defense_Support_Program

https://www.lockheedmartin.com/content/dam/lockheed-martin/s...