Do long range anti-air IR missiles exist?

[michaelemouse]

Semi-active radar homing (SARH) missiles have the disadvantage of needing midcourse guidance and terminal illumination when the launching faction might prefer to be doing something else than weapons guidance. Active radar homing (ARH) missiles tend to be the most expensive and usually require midcourse guidance anyway if they want the target to be within the missile seeker's 20-30km independent acquisition range.

How about 100km+ range anti-air missiles which rely on pre-set intercept point or midcourse updates until they're close to the target then rely on an IR seeker to find the target during the terminal phase? It could be cheaper than using an active radar seeker. Its terminal phase guidance would be passive and therefore stealthier. Since midcourse updates only require tracking quality signal rather than targeting quality signal, the target might never realize it's being targeted.

There is the risk that without midcourse updates, the target would fall outside seeker range in terminal phase but the same thing can happen with ARH. It would also have a more difficult time dealing with targets at lower altitude but I understand that a missile's radar seeker which has a small antenna, low power and limited processing power might have a similar problem. It would have quite poor range resolution but higher azimuth/elevation resolution which seems like it would matter more in terminal phase. Proportional navigation might be good enough in terminal phase. Imaging infrared might be better than a radar at target discrimination. At high altitude, its seeker might have greater range than active radar seekers since IR's limited range chiefly comes from atmospheric attenuation.

So, how much is this a possibility? What liabilities would it have?

[weasel1962]

mica ir or r-27et comes to mind but if a target can be picked up by radar, it makes sense to just hit it with a radar guided missile rather than just mid course guidance.

[zero-one]

what about Aim-9X block 2 or 3. IR with data link. It doesn't make sense to put 2 seekers. If can be picked up by radar, why not just use radar to hit it? Unless IR offers substantially more accuracy

Or maybe the goal is to have the missile use 2 seekers for cross checking and counter counter measure purposes.

[popcorn]

mica ir or r-27et comes to mind but if a target can be picked up by radar, it makes sense to just hit it with a radar guided missile rather than just mid course guidance.

Also the A2A variant of Stunner fitted with both an active RF seeker and IIR seeker for the best of both worlds.

[f4u7_corsair]

The only true medium range IIR missile so far would be MICA IR. Unlike the R-27ER, it is fitted with a datalink. 9X is as well, but quite shorter legged.

[hornetfinn]

There is the risk that without midcourse updates, the target would fall outside seeker range in terminal phase but the same thing can happen with ARH. It would also have a more difficult time dealing with targets at lower altitude but I understand that a missile's radar seeker which has a small antenna, low power and limited processing power might have a similar problem. It would have quite poor range resolution but higher azimuth/elevation resolution which seems like it would matter more in terminal phase. Proportional navigation might be good enough in terminal phase. Imaging infrared might be better than a radar at target discrimination. At high altitude, its seeker might have greater range than active radar seekers since IR's limited range chiefly comes from atmospheric attenuation.

So, how much is this a possibility? What liabilities would it have?

IR seekers have the problem that they have to choose between range and search area. If the optics is good for range, then the search area will directly suffer as it would have very narrow Field of View (FoV). If the FoV is wide then the search area is large, but range will directly suffer. There is not enough space in missile seekers to have optics that is good for both.

Range performance depends on target properties. Against some targets IR seeker will have much superior range than radar and vice versa. I'd say that radar usually has superior range performance and is much less affected by weather for example. Of course IR seeker is totally passive, which would be good as it makes it more stealthy attacker.

You are correct that IIR seekers have better target discrimination and ID capabilities as it has higher resolution due to wavelengths involved. Radar naturally has far superior range resolution which gives it own advantages.

A real problem with long-range IR missile is the seeker window heating which directly affects performance. A long-range missile has to be fast to reach a target in time and the seeker window would heat up and the system might well become useless before it reaches the target. It would be possible to shield the seeker window with detachable shield, but that adds pretty significantly complexity and cost.

[collimatrix]

This idea was definitely looked at. Look up the AIM-97 Seekbat and AIM-152 AAAM.

Historically, I don't think the concept would have worked well. The infrared seekers in the analog electronics days were fiddly. Listen to the radio recordings of the USN pilots splashing Libyan SU-22s and MiG-23s; they spend a lot of time trying to get good missile lock tone. I think the hand-off from SARH to IR homing would have been technically challenging. It's probably much easier with modern digital electronics.

Heating of the sensor dome doesn't seem like that much of a problem. A lot of AIM-9 models had gas-cooled seeker heads. The AIM-9 was also a lock-on-before-launch missile, so on the gas-cooled models the host aircraft would need to pump argon to chill the seeker heads to get them up to ideal sensitivity.

On a hypothetical long range AAM with terminal IR homing, just include a little tank of evaporative refrigerant to flash-chill the seeker head right before the sensor hand-off from radar to IR occurs. True, the tank would need to be on the missile, but it wouldn't need to last as long because the IR seeker is only being used in the very last phase of the missile's flight. This is a long range AAM we're talking about, so a coolant tank wouldn't be an enormous mass driver, relatively speaking.