IR guidance IRL

[nickexists]

I'm wondering how an IR missile calculates it's intercept angle. A radar missile launched in HOJ mode fly pure pursuit (doesn't lead the target), presumably because without any ranging information the missile can only fly towards the target. But as far as I know IR missiles don't have any accurate way to getting a range either so how do they know how to intercept?

[Frostie]

Proportional navigation, something along the lines of the missile using the error that is being presented in the seeker ie. a target constantly moving from centre, and converts that to an intercept.

[nickexists]

Just looked it up, cool stuff. Shouldn't a radar missile in HOJ be able to do the exact same thing?

[lunaticfringe]

Nope. Research the methods of countermeasures and you'll understand why.

[nickexists]

Nope. Research the methods of countermeasures and you'll understand why.

 

That's a big subject. If you already know then why don't you enlighten me?

[lunaticfringe]

It is a big subject, and others (such as David Adamy in his 101, 201, and 301 series) have already pared down into bite-sized examples.

 

http://www.amazon.com/Ew-101-Electronic-Warfare-Library/dp/1580531695/

 

I've spent the time to go beyond that and understand the lower level interactions going on. Problem is, those books already explain what you would want to know better than I (or anyone else here, for that matter) can do. So why try?

[GGTharos]

To add to what lunaticfringe is saying, yes and no. Depends on the jammer type and the missile's capabilities.

 

In the big picture, HoJ is really more of an ability for the weapon to be launched against a target whose data (range, azimuth, altitude, velocity) always was or has just become invalid. Pk obviously goes down.

 

Just looked it up, cool stuff. Shouldn't a radar missile in HOJ be able to do the exact same thing?

[Bushikatagi]

I've spent the time to go beyond that and understand the lower level interactions going on. Problem is, those books already explain what you would want to know better than I (or anyone else here, for that matter) can do. So why try?

 

Maybe because that's a $100 textbook and he's just asking a simple question. Besides the answer is yes, a HOJ missile can do proportional navigation just like an IR missile can.

 

An IR missile does navigation by knowing the bearing of the target (technically the derivative of the bearing for PN navigation) and guessing the closing speed. The same is possible for a missile fired on a jamming target as the bearing is known (it has to be or else the missile wouldn't be able to follow a pure pursuit either).

[GGTharos]

It might be able to utilize PN against an AOJ target, and that soft of weapons employment is certainly supported.. But HOJ is still about launching a weapon with invalid target parameters, so Pk is low.

[Dirty Rotten Flieger]

This is interesting. I'm trying to understand it.

 

I think the basic idea is that when two objects are on a collision course, the angle of line of sight won't change.

 

So if we are both flying jets and on a collision course and I am looking at your jet my head won't turn. I'll just keep looking the same angle till we hit.

 

Maybe it's as simple as that? If the seeker sees the angle is changing it alters the flight path so the heat source stays in the same angle off it's bore sight.

 

Gee that seems a lot simpler that I expected it to be. Maybe I am forgetting something.

[GGTharos]

Yep, it's "that simple".

 

That's pretty much proportional navigation. There are more advanced forms of it that some missiles use as well.

[Ragnarok]

HOJ not calculated velocity vector, but it does not work most of the older IC missiles. Not to bore with explanation from me, you can find how it works "the system with three mirrors" in IC (GSN detector or principle of Cassegrin telescope).

 

My translate serbian-english document (imprecisely)

1. aerodynamic cap

2. formwork

3. The magnetic mirror

4. The secondary mirror

5. corrective lens

6-mesh filter (modulating disk)

7. The photo-resistor

Edited March 18, 2015 by Ragnarok