You can’t just skip positions if the mirror moves linearly across the FOV. If you want to go from one side of the FoV to the other the only way to do so by moving through whatever is between those two points. The mirror can’t just teleport to a new position. I guess you could speed up the scanning of the sections you want to avoid, but considering the thing is already scanning 80 times a second getting it to speed up and slow down without messing up the image processing for the rest of the frame is no small engineering task.
I’m sure the IRIS-T is resistant to LDIRCM, what I’m less sure of is if it is meaningfully better than any other IIR missile.
Where’s that from by the way? In this video the seeker image quality of IRIS-T looks pretty terrible compared to ASRAAM images you shared:
Simple: A Shutter. The shutter is closed while the optics move to the next line to scan. Instead of opening on a line it keeps being closed for the one line in question and opens only at the line after that.
With a Focal Array like the ASRAAM or AIM-9X (128x128 pixels) you can’t do that.
You can though, the same way you deal with the sun; the smaller the aperture in the optical train the less light from the scene get though to the detector array so you minimize what you can see, or use the optical train to deliberately defocus the image on the detector or you use the very low gain Sun-Staring detection diode.
And is there any evidence at all that such a system is used on IRIS-T?
The cost and complexity of implementing such a system seems disproportionate to the benefit when evidence suggests that all IIR seekers are inherently highly resistant to LDIRCM. You’d need a shutter that can close and open again within in less than 1/5000 of a second, do so 80 times per second, and stay perfectly in sync with the sensor while the missile is pulling over 50g.
All of that work for a seemingly fairly marginal benefit. Particularly considering that at the time IRIS-T was being designed there was not a single operational LDIRCM system fielded anywhere in the world.
Isn’t it necessary to have a shutter for a line-scan device? Otherwise you would get streaks/motion blur on the image as the semiconductor cells never get properly discharged. Same effect as if you move a camera too fast causing motion blur. Every commercial line scan camera I found has a shutter (of varying type). Shutter times of 1/5000 aren’t that uncommon by the way as they can go up to 1/16.000 for consumer cameras (and that was 2012).
I’m not aware of scanned focal plane arrays requiring a mechanical shutter but it is really not my area of expertise.
From what I can tell from a quick search in the late 90s when IRIS-T was developed, cameras topped out at around 1/8,000. And those cameras didn’t have to function under more than 50 g’s of lateral acceleration.
So what I found: A line-scan camera has to use a shutter, otherwise the picture would be just “muddy” (they don’t work without a shutter). However modern cameras use electronic/global shutters without moving parts by activating and deactivating the CMOS cells.
If it’s an electronic shutter the g-forces are irrelevant.
But then the only advantage against LDIRCM would be the extremely short exposure time of the cells the moment they look directly into the LDIRCM transmitter (0,1 - 0,2 ms for one line scanned, 12,5 ms overall over one second or 1,25% of the time).
We dont know what the IRIS-T was actually tracking in this video, so its kind of wild of you to state the seeker image quality looks terrible when you dont even know what you’re looking at in the first place. Could be a small drone with a comparatively large IR source attached for example.
Or you know, you can go around the point you dont want to scan, rescanning an area you’ve already scanned? The seekers controller would know the position of the mirror at all times through the scan, since that info is required for constructing the final image from the scan, so it can just have the mirror pass through zones its already scanned and just omit said duplicate data from the final image processing. Its not like the mirror only has 1 DoF…
Its theoretically intensity gradient tracking at that point as a method of DIRCM HoJ, so it doesnt actually need an overly accurate image, it just needs to know where the approximate brightest spot that remains within the expected angle-gate. Dont need a whole lot of accuracy in tracking an intensity gradient…
Could also be a very distant target with maximum magnification and the pictures only shows a section of the image (the three pictures get gradually bigger the later they are in time).
The mirror itself does only have one degree of freedom, it spins around a fixed axis to sweep a 128 px tall row of pixels across a 128 px wide FOV to generate a 128 x 128 image. You seem to be suggesting the seeker scans the FOV like in the left image, it actually scans it like the right image (these are 5 x 5 images instead of 128 x 128 because I can’t be bothered to colour in that many squares).
Sure I guess the missile could hypothetically move the FOV around within the field of regard to try and force the mirror to miss part of the frame, but that would require some insanely rapid and precise seeker movement.
I doubt it is footage of a distant target because it seems to be synced near perfectly to the other two videos that show the missile hitting the target (whatever it is).
Piezo-electrical acutated mirrors used in aerospace applications can do that extremely well and have no problems with g-forces. Things like PIRATE use Piezo electric actuated mirrors to compensate vibrations for example. Wouldn’t be difficult to actuate the mirror so that it skips a line.
Moving the mirror inside the seeker is not the same as moving the seeker optics. Which are you talking about? You quote a part of my message about moving the seeker optics then talk about moving the mirror.
I thought we were talking about the ability to skip a line via the optics? By using a piezo actuated mirror (or prisma) inside the optics you wouldn’t have to move the seeker optics at all.
How would you skip column 3 with the laser in it? As far as I can tell, the mirror in the these images typically rotates around a fixed axis to sweep the linear detector across the fov. So if you want to scan columns 4 and 5, the mirror must move over column 3 to get there. You can move it very quickly over column 3, but at the end of the day the mirror is still moving over column 3.
Theory: You could let the mirror focus the line in question outside of the sensor array so the energy is directed onto an absorber block of sorts. The sensor then will only see “black” for this line as the energy/light never reaches it.
I think Typhoon is the only top tier CAS jet that needs to linger while it guides it’s Brimstone like a Pseudo Bullpup. Makes it so vulnerable to IR SAMs, IFVS and now Tanks with delayed rounds.
Not only do you have to worry about the big powerful sams but the shtty little ones too.
I can only imagine the power having FnF CAS would give you.
Against an IR threat, that is entirely on the shoulder of the MAWS to detect, deploy CMs and direct the pilot into the best maneuver to evade.
Though also just flying high helps a lot against those too and only dropping down low when really needed, like with a gunstrafe, at which point you’d do what Mike Sutton did in his book, throttle down and approach with the sun behind. Make a MANPAD shot quite hard
But this is entirely ahistorical remember. We are forced into such tactics because we dont have our IRL weapons.
They would not be using 15km SAL weapons in an enviroment that contained known Anti-air assets. Youd fire off a volley of Brimstone 2s at 60kms
