As an Engineering Project Manager, why would I not include a mission critical subsystem in the design? Answer...Look at what France has done with the Rafale. IRST is a secondary and OPTIONAL sensor system for both platforms. Sure would be nice to have, but it doesn't affect things enough to stop operational status.

Look at what an F-22 is designed to do. If having an IRST would offer any advantage it would be deployed. There are reasons why the F-22 is hauling around an insanely expensive APG-77 with no IRST for BVR work. There is a reason the Rafale has it's RBE2 as a mission critical subsystem while the IRST was considered an option. Seriously this is a non issue to bog a thread down over.

I know why it happens with IRST however. People think IRST's invalidate stealth technology and this is FALSE. IRST are just as vulnerable to stealth techniques as well. In fact todays stealth aircraft are designed with these features. Here is an analogy and I pray this gets through. Go outside. Look up. There are dozens of aircraft up there you can't see because they are too high and they get lost in the background(noise). Get a pair of binos and you SNR goes dramatically down. But there is a trade off. YOU NEED TO KNOW WHERE TO POINT THE BINOS. Otherwise you will not be able to search with the same efficiency. IRSTs operate like that at range. SO what you need is a radar that can blast EM energy out there over a wide arc and then listen for a return. Because you sent that signal in the first place, you know an aweful lot about it based on the characteristics of the returning signal. If you choose to, and the IRST has the range, you can slave the IRST to the last known position of the target and see it. BUt all you really know is that an IR emitter is on that bearing. You don't know if its coming, going, how far or much of anything else. If you can get close enough, you may be able to make certain assumptions. But the data is never going to be as precise as a dated signal source you control. This begs the question of how important is the capability. Thats mission dependent and by the simple fact that neither the F-22 or current Rafales have an IRST, not very. The moral of the story is...

IRST is certainly useful but cannot take the place of a radar.

-DA 

BW,

I know there are some very capable IRST's out there. I know that a skilled pilot could use one to make a surprise attack. But I also know that the range is limited due to attenuation of the signal. If you are reliant on an IRST to conduct BVR, you will be at a serious disadvantage to most other aircraft equipped with a radar. If IRSTs were as capable as you say they are or if they worked the way you are saying, I suspect that they would be a major feature in almost every combat aircraft design. THAT IS NOT THE CASE. Think about it like this. A fighter with a radar as powerful as the F-15 or Mig-31 still rely on AWACS and/or GCI to be guided to their targets. This is because the sky is HUFREAKINGMUNGOUS. Small fighter radars can only scan a very tiny portion of the sky. And we know that these radars are not nearly as attenuated by weather, aspect angle and they have the advantage of control of the signal. Knowing this, you cannot possibly be arguing in good faith that an IRST is going to be an acceptable replacement for a radar. What you are saying is like comparing an AIM-120 to an AIM-9 for BVR combat. I'm familiar with a lot of the various techniques and data I've seen suggest best case ranges for simple detection of less that half what you state. When you mention actual engagements and tracking, think 5 to 20km depending on conditions. That takes into account TMA, atmospheric propagation, LRF and apparent surface of the tgt. BW, it's just not the same as radar.

-DA 

-DA