Liquid Nitrogen (LN2) Pour Filled Dewar Cameras

[Fraser]

Interesting. As you can tell, this is not the sort of thermal imager I normally deal with. It definitely had the Risley Prism system though.

[coppice]

Interesting. As you can tell, this is not the sort of thermal imager I normally deal with. It definitely had the Risley Prism system though.

Interesting. I thought LANTIRN was late enough that it would use a full image sensor. Either way, its not like the ground mapping line scanners. They only have a single pixel sensor, spinning on the edge of a vertical disc, sweeping the ground below. As the plane moves forward they achieve a raster scan. The electronics needs to manipulate the geometry of the scan, to allow for the actual forward speed of the plane, and may do the image manipulations needed to correct for the plane's attitude as well.

[Fraser]

I just found the detail on the LANTIRN system and I can confirm that the unit I advised on was part of the navigation pod and provides a forward thermal view of the terrain that is presented to the pilot on the HUD. It all gets very confusing with the various similar looking pods, some with fixed heads, others with moving ball heads and modern versions doing the job of both the navigation and targeting pods in a single unit. As I said, not my area so this is uncharted territory for me beyond the basic design of the thermal imaging camera core.

https://www.oocities.org/capecanaveral/5415/lantirn.html

From the provided information I can also confirm that the pod contained an “environmental control” section so that was likely why it had fluid pipes in the camera section.

Fraser

[coppice]

I just found the detail on the LANTIRN system and I can confirm that the unit I advised on was part of the navigation pod and provides a forward thermal view of the terrain that is presented to the pilot on the HUD. It all gets very confusing with the various similar looking pods, some with fixed heads, others with moving ball heads and modern versions doing the job of both the navigation and targeting pods in a single unit. As I said, not my area so this is uncharted territory for me beyond the basic design of the thermal imaging camera core.

https://www.oocities.org/capecanaveral/5415/lantirn.html

From the provided information I can also confirm that the pod contained an “environmental control” section so that was likely why it had fluid pipes in the camera section.

Fraser

If its specifically described as terrain imaging, it must have been for ground hugging missions at night. Mechanically scanned imagers usually have a rather low refresh rate. I wonder what this one achieves? A pilot needs something good if they are following the terrain at high speed.

[Fraser]

The image presented to the pilot appears decent but no idea of the frame rate. I attach an example image and, as you say, it appears to be for low level operations. We had better shut down this interesting ‘conversation’ now as we are way off topic for this thread

Thanks for your insight into military aircraft thermal imaging systems 

Fraser

[coppice]

Thanks for your insight into military aircraft thermal imaging systems 

If you are interested in thermal imaging, this is the killer application. 

[CatalinaWOW]

I just found the detail on the LANTIRN system and I can confirm that the unit I advised on was part of the navigation pod and provides a forward thermal view of the terrain that is presented to the pilot on the HUD. It all gets very confusing with the various similar looking pods, some with fixed heads, others with moving ball heads and modern versions doing the job of both the navigation and targeting pods in a single unit. As I said, not my area so this is uncharted territory for me beyond the basic design of the thermal imaging camera core.

https://www.oocities.org/capecanaveral/5415/lantirn.html

From the provided information I can also confirm that the pod contained an “environmental control” section so that was likely why it had fluid pipes in the camera section.

Fraser

If its specifically described as terrain imaging, it must have been for ground hugging missions at night. Mechanically scanned imagers usually have a rather low refresh rate. I wonder what this one achieves? A pilot needs something good if they are following the terrain at high speed.

Frame rate, scan speed and sensitivity are a trade space.  Many scanners of the era achieved frame rates well above the effective frame rate of a human pilot (20-60 fps range).

The rotating wedge system can generate a large number of scan patterns with the interesting property of widely varying scan rates over the field.  Thus information can be gathered over a large field of view with a small number of detectors, and very high quality, data information provided over a small region. 


For MrSheep - Just about every cooling gas imaginable has been used for cooling infrared systems.  Helium for systems that need really low temperatures, Neon for slightly less demanding cases.  Nitrogen and argon are widely used, and for roughly similar temperatures.  Nitrogen is widely available and cheap, argon has desirable thermodynamic properties.  Oxygen is rarely used because of fire danger, but compressed and dried air is sometimes used in cryostats.  There are even systems that use Freon and CO2.

[Fraser]

I will see whether I kept the images of the F-15 navigation pod and start a new thread about it as such might be interesting to forum members. It is not often that we get to see the inner workings of military thermal imaging systems, albeit older technology in this case.

Fraser

[Fraser]

I have found the images of the LANTIRN Thermal navigation pod internals  I am having some doubts about posting such in the public domain though ! The unit was dated 2001 so not exactly ancient technology. Posting technical pictures and details of an F-15 related thermal imaging technology may not be the brightest of ideas. I was surprised that the scrap dealer obtained a complete pod that was actually unused stores stock with only 4 hours on its cooler. When discussing the more advanced thermal imaging technologies we do have to consider why such is not already documented in the public domain.

Anyway, apologies to the OP for the off topic discussion. Now back to the topic of LN2 cooled cameras 

I own two LN2 cooled cameras, the AGA 680 thermal microscope and the AGA 780 series portable thermal imaging scanner. Neither will ever see LN2 again as they are museum pieces. I did look into sourcing LN2 and what the costs would be. Sadly in the UK, unless you are well connected with a Technical University, it is actually quite hard to obtain small quantities of LN2 on an ad-hoc basis. The storage Dewars are quite expensive as well. It quickly became apparent to me that the cost of providing LN2 for my two antique cameras far exceeded any benefit of getting them running. The situation with the LN2 cooled Amber cameras is very different though. Those cameras are worth the cost and effort of the LN2 sourcing and associated equipment. I was not previously aware of the need to refresh the vacuum on the dewars of those detector housings and was similarly unaware of the extensive equipment requirement to pull that vacuum to the required level. As has already been stated, these cameras are well suited to science roles where LN2 and associated vacuum pumps are more common. I will stick to Stirling coolers and can understand why the Stirling mechanical cooler was such a welcome development for many industrial users of cooled thermal imaging systems. We actually had an AGEMA THV880 scanning thermal camera upgraded to a Stirling cooler by AGEMA in Sweden. We were one of the first to have that upgrade installed and it cost a small fortune.

Pictures added…

AGEMA 880 LN2 model
AGEMA 880 with Stirling Cooler upgrade mounted on rear
AGA 780 series portable LN2 cooled system
AGA 680 LN2 cooled camera …. Early thermal imaging ! Not exactly small or light in weight !

Fraser

[MrSheep]

Fraser, yeah I didn't know that I needed high vacuum equipment either until I read the manual. You learn something new everyday haha 

Also yeah it is kind of a hassle to source LN2. It is easier if you live near colleges or universities as the always get it by the truck load. However not sure how willing they are to give it to you when you are not part of the department. I have however been able to source some near me via welding supply shops. Not all of them have it but some do so you have to do some research and some calling to find some. I know Airgas and Praxair sell it. But the prices near me are a bit too high $10/L. Luckily I found a store that was less at $5/L

I will prob not use the LN2 cameras as much as well but will from time to time because I do want to play around with them more.

[MrSheep]

Cool video on servicing a LN2 Detector system 
Although I do question is it safe to just pull the vacuum port like that. I at least pump mine down to rough vacuum (5mbar) before I attempt to remove the plug.

[DaJMasta]

A little bit of a necro, but a very similar topic probably relevant to very similar people:

I've recently got my hands on a very interesting cooled camera that uses an LN2 dewar with a fill port I'm having trouble making sense of.  I've talked to the company that made it and while they were quite helpful, they ultimately couldn't provide software or documentation for it - they claimed it was a legacy product out of support and that they had no software for, but I suspect it was a precursor to a current product and it never ran on published software or with guaranteed specifications.

In any case, that means it's time to poke around and see what I can get working, and the fill port on the dewar has a lot of fittings and seals that I wouldn't expect to see.  I've included some pictures, but can anyone with more experience than I make sense of it?  I was expecting a non-screw-down plug, since the boiling nitrogen would need an escape route, but instead I've got a hard plastic insert into the neck that seems to be stuck in place, a large grub screw as a cap for the center, and a pair of smaller pipe fittings on the side of the neck of the dewar that have plugs with small holes.

Best guess, the grub screw in the plastic insert covers the fill port and the side pipe fittings are the vents for the gas, but it also doesn't seem like they're currently opened - a brief low pressure test makes it seem like no gas can enter/leave (maybe the fillport is still closed?)

In any case, can someone shed some light on how this should operate before I risk further disassembly?

[MrSheep]

Ah yes I have an Amber Dewar that houses their 256x256 ROICs with a very similar port. So the top port is where you put the LN2. The side ports are pressure relief valves. Since the top is screwed on, LN2 expands very rapidly (700x in volume) when it evaporates. So in order to not create a bomb. The pressure has to be released somehow. The other LN2 dewars I have, Do not have screw on caps, but rather a loose fitting plug is used periodically letting gas escape.

Are you able to pull on the brass part of the valve. You should feel some spring pressure. This is to check if those valves are not stuck

Also do you happen to have a turbo molecular pump or high vacuum system? This is need to pump down the dewar. If not I wouldn't risk pouring LN2 into the dewar until you can confirm the vacuum is good.

[coppice]

The military could not cart around bottles of unsealed Liquid Nitrogen so other cooling methods were investigated.

Really? It never stopped them. The 70s thermal imaging I worked on and that I am aware of all used dewars of liquid nitrogen. The main problem with liquid nitrogen is its a liquid. It sloshes around. Most thermal imaging applications are mobile, even in something that doesn't do many wild manoeuvres, like a helicopter doing simple observation work. In another message you talked about orientation issues. Although its a long time ago, and I can't remember what short of slosh control measures were in our systems, sloshing was definitely a big deal, whatever the orientation.

[DaJMasta]

@MrSheep very much appreciated!  The brass sections come out very easily and when I pull one out I can confirm that now blowing air into the chamber from the fill port completes the circuit so to speak.  There is mention in the literature that one design goal was long (8h+) duration operating time on a fill, and I suppose the smaller port and sealed system is a way to insure that.

As this camera purportedly has some operating uses at room temperature, I will probably try LN2 as a check to see if the dewar sweats, but I've got a full vacuum system, so if it needs to be evacuated, it will take some fittings, but can be done.

[MrSheep]

Nice! Yeah the only part that you need then is the vacuum operator, it is shown earlier in this thread. It cost around $300ish and can be KF or CF.

One thing to note on these operators is to not screw them on too much. Once I evacuated a dewar and ended up not being able to separate the screw plug from the operator shaft, It kept spinning inside the vacuum port. I had to re-evacuate the system again . While not under vacuum test to see if the operator shaft can unscrew off of the plug without having it spin in place.

[Fraser]

Coppice,

An interesting insight, thank you. How did the Army & Special forces recon units, that spent days away from base, cope with the finite LN2 life before it boiled off ? As I read your post, I had mental images of our guys yomping across the Falkland Islands and finding that their thermal surveillance scopes were useless because the LN2 would have boiled off during the journey. The fact that LN2 boils off whether or not the scope/camera is used can be an operational support problem. The Argon Gas / Air cooled scopes/cameras did have a finite run-time but the gas was only used when the unit was actually in use.

Fraser

[coppice]

Coppice,

An interesting insight, thank you. How did the Army & Special forces recon units, that spent days away from base, cope with the finite LN2 life before it boiled off ? As I read your post, I had mental images of our guys yomping across the Falkland Islands and finding that their thermal surveillance scopes were useless because the LN2 would have boiled off during the journey. The fact that LN2 boils off whether or not the scope/camera is used can be an operational support problem. The Argon Gas cooled scopes/cameras did have a finite run-time but the gas was only used when the unit was actually in use.

Fraser

The only thermal systems I saw in the 70s for army use were fixed to vehicles. The stuff I worked on was for airborne use. The fire services had hand held mechanically scanned thermal cameras, but I never saw one of those close up. I think they were pretty basic, for cost reasons. The Falklands war was sufficiently after I did that work that I expect things had moved on. Things were quite bulky and heavy in those days, though, so anything being carried long distances would have had to be very basic.

[CatalinaWOW]

 As far as I know, in that era the army had no foot mobile infrared.  But they did have image intensifiers, which were was pretty new still.  About like uncooled IR a decade ago.  Well developed for well heeled players, but out of reach of those limited to the budgets
Of smaller nations.

[MrSheep]

Found an interesting article while looking for information on Amber Raytheon Cameras. Saw some information on Liquid nitrogen cooled arrays on page 33

"U.S. Air Force and Navy aircraft of the 1950s and 1960s, such
as the F-101B Voodoo, F-104 Starfighter, F 106 Delta Dart,
F-8 Crusader, and F-4B Phantom, were equipped with these
early sensors. Air Force interceptors carried nose-mounted,
nitrogen-cooled, lead selenide (PbSe) cross-array IRST sets
to detect high flying Russian bombers, such as the Bear and
Bison. "

https://dsiac.dtic.mil/wp-content/uploads/2021/10/DSIAC-Monograph-FLIR.pdf

P.S. Worth it to read the entire thing, learned a good amount on the history of IR in this one read

[Fraser]

This is the beastie that I was thinking of when discussing the gas cooled surveillance  thermal imaging systems used in the military. It was made by Thorn EMI.
I note that this example has a date code of 1991 and documentation for it shows 1987. As has been stated, this is after the Falklands conflict of 1982. The units internal design principals appear similar to that of the Hughes Probeye Argon gas cooled thermal imager that was available in 1974 !

https://www.prc68.com/I/ThermalIMagerDFOV.html

Hughes Probeye….

https://www.prc68.com/I/Probeye.shtml

Fraser

[Fraser]

MrSheep,

That document you referenced is a very interesting read. Thank you 

The Javalin AT system is detailed…. I expected more thermal pixels in the missiles seeker head (64x64 pixels FPA) for a system designed as an anti-tank direct and indirect fire weapon. It just goes to show that it is not always about how many thermal pixels you have, but rather how you use them 

Fraser