I was looking and saw that the British developed a missile called the ASRAAM, which was not adopted by the United States. Why? Also, how do the AIM-9X and ASRAAM compare? In which situation would one be better than the other?
Why was the ASRAAM not adopted by the USA? Officially the ASRAAM was evaluated in the context of tender. The entries were the AIM-9X Sidewinder and the ASRAAM. However it was rejected as a result of tests conducted during that evaluation (link). Therefore, simple as that, the missile was evaluated and found to be not satisfactory, or less satisfactory then its competition (the AIM-9X).
I could however not find a source citing if explicit reasons where given. However a lot of speculation emerged if this decision was based on factual reasons such that the ASRAAM could not be deployed on aircraft carriers, does have unsatisfactory turning performance shortly after firing or if the sidewinder simply had more value because exisiting motor sections could be reused (apparently 20.000 of these sections were still around and could be reused). Other reasons could include political considerations: Perhaps the USA did not want to buy "foreign" material. But again, that is speculative.
Which of the two missiles is better? This very much depends on requirements. Both missiles use the same Hughes IR Seeker (a focal plane imaging array seeker). Both have a very similar combat deployment scenario: That of a short-range engagment. The key differences are:
- The ASRAAM has higher range due to less aerodynamic drag and a bigger motor
- The AIM-9X is better at initial turning rate which offers an advantage shortly after the missile leaves the launch rail.
- The AIM-9X has a smaller diameter (127mm vs 166mm) therefore less space for warhead, motor etc.
- The warhead of the AIM-9X is a bit smaller, therefore less lethal
- There are differences in how both missiles compute their guidance solution in response to flares, resulting in differences in performance in this respect. The exact differences are classified
However interesting to note is that both missiles acquired some upgrade in order to counter these points: The AIM-9x was upgraded in the Block III variant to improve its range (and also to gain a lock-after-launch capability), while it was apparently important for BAE to issue an upgrade for the ASRAAM which enables it to hit targets behind the aircraft (also coupled with lock-after-launch capability).