Of DAS, EOTS etc..

Cockpit, radar, helmet-mounted display, and other avionics
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quicksilver

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Unread post13 Apr 2020, 17:17

“If you see a dot moving across the horizon, you don't know if it's an F-35 cruising at subsonic speeds 100km away, or an F-22 flying at supersonic speeds 200km away - the amount of IR energy that arrives at your sensor can be the same if the F-22's higher IR output is matched by the inverse-square law delivering less of that energy to your sensor.“

...or a Falcon rocket launched from a location in Florida several hundred miles away. 8)

IR sensors very good at DOA.
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Dragon029

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Unread post14 Apr 2020, 03:21

ricnunes wrote:Well, with DAS you also have multiple sensors. It has 6 sensors around the aircraft so some or many of the times you can have two (2) DAS sensors looking at the same target which would allow for the same 2D triangulation (between 2 DAS sensors and the target).

DAS sensors on the same aircraft are infrequently / rarely going to be looking at the same target; the more overlap the sensors have, the lower the resolution / performance the sensors have. Also, if you have 2 DAS sensors looking at a target, you have a 3D triangulation, though it'll have limited range resolution given the proximity of the DAS sensors and image resolution limits. But anyway, given that there'll be minimal overlap I don't expect them to have programmed in such a functionality.
ricnunes wrote:But even if it doesn't then I believe you could still build a fairly approximate range solution (nothing too precise, of course) using data such as a generic target/aircraft size, position relative to the own aircraft (F-35), current own aircraft (F-35) speed and heading, apparent target path, gathering if the target getting closer or getting away (could be done by an increase or decrease in pixels) which helps calculate the apparent target path, etc... (not to dissimilar to what happen with passive-sonar tracking on Submarines).

The issue though is what kind of generic target do you select? A fighter? An air-to-air missile? Again, for things like SAMs you can narrow down your assumptions, because there aren't any fighters that can launch vertically and accelerate upwards at several Gs, but for threats detected near or above the horizon, you have a very wide range of possible targets. Sensor fusion with the ASQ-239 or radar can help a lot with narrowing that down, but we're apparently talking only about the DAS's individual capability.
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ricnunes

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Unread post14 Apr 2020, 17:49

Dragon029 wrote:DAS sensors on the same aircraft are infrequently / rarely going to be looking at the same target; the more overlap the sensors have, the lower the resolution / performance the sensors have.
Also, if you have 2 DAS sensors looking at a target, you have a 3D triangulation, though it'll have limited range resolution given the proximity of the DAS sensors and image resolution limits. But anyway, given that there'll be minimal overlap I don't expect them to have programmed in such a functionality.


If you are correct above then I would say that there's 'plenty' of other ways to achieve a successful triangulation even using a single DAS sensor.
For example you previously mentioned something interesting which is regarding the better capability to track a missile launched from the ground due to have a launch-point on the ground. I guess that you can do the same regarding tracking air targets such as an aircraft such as for instance:
1- A point on the ground is generated or used (it could be an existing waypoint or a Bullseye or any other generated point generated "on the loop"). The distance and direction (resuming, the position) of such point from the F-35 is of course well known. Afterall everything on the F-35 communicates (sensor fusion).
2- The own F-35 position is obviously well known.
3- The direction of the aerial target is also known due to the (even if lone) DAS sensor.

So with the 3 points above you should be able to create a successful triangulation and with that know roughly the target's position and range.


Dragon029 wrote:The issue though is what kind of generic target do you select? A fighter? An air-to-air missile? Again, for things like SAMs you can narrow down your assumptions, because there aren't any fighters that can launch vertically and accelerate upwards at several Gs, but for threats detected near or above the horizon, you have a very wide range of possible targets. Sensor fusion with the ASQ-239 or radar can help a lot with narrowing that down, but we're apparently talking only about the DAS's individual capability.


Well, I would say that there are also some possibilities to discriminate between an aircraft or a missile. For example during the missile's launch DAS can clearly see missile plumes and those plumes can be seen from very far away (as seen in the DAS rocket test video). So such targets would instantly be classified as missiles.
The other remaining aerial targets could be classified as aircraft. I guess that a fighter size would be fine in case it isn't possible to gather any further size data on the target, this either by DAS or by any other sensors (such Radar, EOTS or Barracuda). In case if the target is for example a Bomber or a Cessna 172 then the range solution would be much less accurate but this wouldn't be nearly as critical as it would be compared to a fighter aircraft, I guess.

And about the above I would even add the following:
- If the aerial target is closer to the F-35 and as such closer to a DAS sensor where the target can be presented as several pixels than DAS should be able to ID the target (due to its shape) and thus gather its size.
- If the aerial target is farther from the F-35 and as such farther from the DAS sensors where the target is presented as a single pixel which means that DAS isn't able to ID the target then EOTS could be aimed at the target and as such positively ID the target and thus gather its size.
- Target ID can also be gathered resorting to the Barracuda (ASQ-239) like you said but for this the target must be emitting or otherwise the ASQ-239 won't help.

But an independently of the above, the (official) video that I'll share below clearly hints that DAS performs target ranging, this after minute 1:50 where it is stated the following:
Situational Awareness IRST is also a key function of DAS
DAS detects and tracks approaching aircraft from any angle reducing the potential of mid-air collisions


So DAS being an IRST and being capable to detecting an tracking approaching aircraft in order to even avoid potential of mid-air collisions then it certainly must have ranging capability.

“Active stealth” is what the ignorant nay sayers call ECM and pretend like it’s new.
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quicksilver

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Unread post14 Apr 2020, 18:09

“So DAS being an IRST and being capable to detecting an tracking approaching aircraft in order to even avoid potential of mid-air collisions then it certainly must have ranging capability.“

The answer is hiding right there in plain view — that’s a two-ship angle/angle triangulation.
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wrightwing

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Unread post14 Apr 2020, 18:56

Dragon029 wrote:


DAS sensors on the same aircraft are infrequently / rarely going to be looking at the same target; the more overlap the sensors have, the lower the resolution / performance the sensors have. Also, if you have 2 DAS sensors looking at a target, you have a 3D triangulation, though it'll have limited range resolution given the proximity of the DAS sensors and image resolution limits. But anyway, given that there'll be minimal overlap I don't expect them to have programmed in such a functionality.






Actually being staring arrays, DAS sensors are continuously looking at everything in their field of view. Additionally, DAS provides over 540° of coverage, so yes 2 sensors could see the same target. That's why there's seamless coverage, because each sensor's FOV doesn't stop where the next one starts. Every sensor overlaps with the one next to or across from it.
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quicksilver

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Unread post14 Apr 2020, 21:33

“Actually being staring arrays, DAS sensors are continuously looking at everything in their field of view. Additionally, DAS provides over 540° of coverage, so yes 2 sensors could see the same target. That's why there's seamless coverage, because each sensor's FOV doesn't stop where the next one starts. Every sensor overlaps with the one next to or across from it.“

The areas where they overlap are somewhat limited — which I took to be his point. Thus, ‘DAS’ — by itself...one lone sensor — has virtually no range estimating ability unless and until it is combined with other inputs from other sources, whether they be own-ship or off-board.

How do you spell ‘fusion’? :wink:
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wrightwing

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Unread post14 Apr 2020, 22:17

quicksilver wrote:“Actually being staring arrays, DAS sensors are continuously looking at everything in their field of view. Additionally, DAS provides over 540° of coverage, so yes 2 sensors could see the same target. That's why there's seamless coverage, because each sensor's FOV doesn't stop where the next one starts. Every sensor overlaps with the one next to or across from it.“

The areas where they overlap are somewhat limited — which I took to be his point. Thus, ‘DAS’ — by itself...one lone sensor — has virtually no range estimating ability unless and until it is combined with other inputs from other sources, whether they be own-ship or off-board.

How do you spell ‘fusion’? :wink:

~30° per sensor, so yes there are gaps, but I'm not sure I'd go so far as saying "somewhat limited." If the F-35 changes its attitude slightly, it can bring targets back into view. Now combine that with at least 3 other F-35s, and the gaps in coverage disappear.
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quicksilver

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Unread post14 Apr 2020, 23:36

“...so yes there are gaps, but I'm not sure I'd go so far as saying "somewhat limited."

I would. Take a look at where the sensors are mounted and what field of regard exists from each location.

“Now combine that with at least 3 other F-35s, and the gaps in coverage disappear.“

I rest my case. Fusion is not just about own-ship sensors.
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wrightwing

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Unread post15 Apr 2020, 06:48

quicksilver wrote:“...so yes there are gaps, but I'm not sure I'd go so far as saying "somewhat limited."

I would. Take a look at where the sensors are mounted and what field of regard exists from each location.

“Now combine that with at least 3 other F-35s, and the gaps in coverage disappear.“

I rest my case. Fusion is not just about own-ship sensors.

Each sensor has ~30° overlap on either side, by a neighboring sensor, so any 2 sensors will have a ~60° FOV. Thats not perfect, but it's pretty significant. Obviously it gets even better as a multi-ship formation.
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quicksilver

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Unread post15 Apr 2020, 15:47

“Thats not perfect, but it's pretty significant.”

I guess we’re quibbling about ‘somewhat limited’ vs ‘pretty significant’... :wink:

“Obviously it gets even better as a multi-ship formation.“

We agree. :thumb:
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wrightwing

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Unread post15 Apr 2020, 20:00

quicksilver wrote:“Thats not perfect, but it's pretty significant.”

I guess we’re quibbling about ‘somewhat limited’ vs ‘pretty significant’... :wink:

“Obviously it gets even better as a multi-ship formation.“

We agree. :thumb:

Would you not agree that a 60° shared FOV between any 2 sensors is fairly useful, even in a 1v1 situation? It's not perfect, but it certainly greatly increases the probability of getting some range/geolocation data. The EOTS could also be slewed for an extra point of reference (as well as radar/ESM.)
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energo

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Unread post15 Apr 2020, 20:42

That LM ditched NG in favor of the upgraded DAS from Raytheon makes you wonder about the rationale behind the decision for canceling the alternative engine way back. :crazypilot:
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wrightwing

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Unread post15 Apr 2020, 20:54

energo wrote:That LM ditched NG in favor of the upgraded DAS from Raytheon makes you wonder about the rationale behind the decision for canceling the alternative engine way back. :crazypilot:

LM didn't ditch NG. NG opted not to compete.
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ricnunes

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Unread post15 Apr 2020, 20:57

quicksilver wrote:“So DAS being an IRST and being capable to detecting an tracking approaching aircraft in order to even avoid potential of mid-air collisions then it certainly must have ranging capability.“

The answer is hiding right there in plain view — that’s a two-ship angle/angle triangulation.


In the video you have a triangulation made by a 2 F-35s, that's correct.
But then again, it should be possible to perform triangulation without a second F-35 (although and granted with a 2nd or better a 3rd and 4th F-35 would be better/preferable), this by resorting to another source. Again, using a second DAS sensor or better yet, the EOTS would provide a good source of ID and triangulation.
“Active stealth” is what the ignorant nay sayers call ECM and pretend like it’s new.
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energo

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Unread post15 Apr 2020, 20:59

wrightwing wrote:LM didn't ditch NG. NG opted not to compete.


Either way, it's interessting that Raytheon saw the potential and developed a competing product which is already now available. Keep 'em comming. :mrgreen:
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