I know this thread has been dead, but I thought I could add a little info.

The idea of using an interceptor aircraft to shoot down a ballistic missile
in boost phase was evaluated by the USAF back in the early 1990s. I think
this happened after the first Gulf War. The USAF considered developing a
very long range AAM to fit underneath an F-15. It would be cued by other
sensors off the aircraft, such as AWACs or even satellites that detected the
missile launch.

The problem was that such a mission really requires around the clock
coverage of a large area. They would have to put many aircraft in the air
and keep them up for long periods of time. Expensive and not easy on
aircraft or crews.

The plan was dropped and the Air Force then evaluated the possibility of
fitting the missiles to long-endurance UAVs. I think that this too was soon
dropped, but am not sure why. One possibility is that UAVs at the time (and
still) lack payload capability and they would have to carry a couple of
heavy missiles, bigger than the AIM-54 Phoenix.

You can find a couple of articles in Aviation Week in the early 1990s
dealing with this subject.

After abandoning this method, they turned to the Air-Borne Laser (ABL)
approach using a big laser onboard a 747. You can look this up on the net.
The program has run into a lot of problems--cost overruns and delays. There
have been rumors of its cancellation, but it is currently limping along.




D