I have found that AMMs apparently cannot intercept ICBMs even if they do spend 5 minutes in orbit, the following is a direct transcript from the log:
7th April 2040 07:37:46,Sol,Salvo of 10x AMM-3 Spartan has intercepted its target. Chance To Hit 0%: (Missile Speed 52500 km/s / Target Speed 10 km/s) x Missile Agility 31 x GradeBonus 8%
7th April 2040 07:37:46,Sol,Missile #1 Missed
7th April 2040 07:37:46,Sol,Missile #2 Missed
7th April 2040 07:37:46,Sol,Missile #3 Missed
7th April 2040 07:37:46,Sol,Missile #4 Missed
7th April 2040 07:37:46,Sol,Missile #4 Missed
7th April 2040 07:37:46,Sol,Missile #6 Missed
7th April 2040 07:37:46,Sol,Missile #3 Missed
7th April 2040 07:37:46,Sol,Missile #8 Missed
7th April 2040 07:37:46,Sol,Missile #9 Missed
7th April 2040 07:37:46,Sol,Missile #10 Missed
The bit that got me was the Chance To Hit 0%. Since none of the ICBMs did hit, it may not actually be true, but it could account for the rather profligate use of missiles. I have the database if Steve's interested.
Regards