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Bash the F-35 thred.


Belesarius
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http://www.lockheedmartin.com/us/news/press-releases/2016/september/160913-rms-f-35-and-aegis-combat-system-successfully-demonstrate-integration-potential-in-first-live-missile-test.html

 

During the Sept. 12 test, an unmodified U.S. Marine Corps F-35B from the Marine Operational Test and Evaluation Squadron 1, acted as an elevated sensor and detected an over-the-horizon threat. The F-35B sent data through the aircraft’s Multi-Function Advanced Data Link (MADL) to a ground station connected to the Aegis Weapon System on the USS Desert Ship (LLS-1), a land-based ship. The target was subsequently engaged and intercepted by a Standard Missile 6.

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The commentator seems very skeptical of LPI (low probability of intercept) techniques for radar and insists that as soon as it turns on its active sensors, a stealth fighter is no longer stealthy.  I am curious why; the idea behind LPI is fairly straightforward and at the very least theoretically sound.  The radar (which has to be AESA to do this) spreads out its emission energy onto multiple, random frequencies instead of using only a single frequency.  The total energy output is still high enough to get a clear picture, but to a radar warning receiver it doesn't look like a radar signal, it looks like random noise.  This, combined with the AESA's extremely precise and rapid beam steering means that hostile ECM will have a hard time determining that it is being pinged.

The receiver has access to the same technology as the transmitter these days, you know. RWR's aren't the kind of 60's thing that simply turns the received radar sweep into an audible sine wave so you can hear it go beep in your headset anymore. Sure, you'll fool older systems but if the other guy has the same level of technology you're back to the radar equation and the defending side always has the advantage of their energy being inversely proportional to R² rather than R⁴. If the transmitting radar can detect the bouncing signal the illuminated aircraft sure as heck can.

Also related, someone on SA posted this thing in response to a post about ~aerospace technology~ in acoustic noise cancelling headphones:

 

I actually have a provisional patent that does that cancellation (super-position of opposing amplitudes at the same phase) through a combination of digital and analogue systems adaptively in real time (<5ns delay , anyway) across broad bands of non-contiguous spectrum.

It works great, we've done > 80 db reduction on a broadband Gaussian white-noise chirp in a lab environment.

If there is an audiophile out there who wishes for this kind of performance please let me know, my rates are quite reasonable and I would be happy to implement this in the room of your choosing for mid 7 figures (hardware included). Unclassified whitepaper available upon written request, US Citizens only please. Military & governmental customers welcome.

e: That ad specifies 1uV on the power supply lines (40 db). Pshah, we beat that by orders of magnitude over RF.

I'm pretty sure I recall Saab mentioning something like this in connection to the Gripen E, and I think that stuff (well all the EW computer thingies in general) is one of the reason for the new cooling air intake on the base of the tailfin. It wouldn't surprise me if that kind of technology is on all the 4.5th generation fighters within the next ten years or so.

edit: then one of the guys who work with future warfare stuff posted this in a different discussion:

It seems to me like emission control is one of the things that laypeople really don't understand very well about the modern battlefield. It is absolutely crazy when you see graphical representations of how emitters "look" to collection assets...it really is like turning on a flashlight in a dark room, except that you can tell exactly who manufactured the flashlight, and when, and you can be pretty sure who the specific owner of the flashlight is, and how much juice the flashlight batteries have left, and etc

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The receiver has access to the same technology as the transmitter these days, you know. RWR's aren't the kind of 60's thing that simply turns the received radar sweep into an audible sine wave so you can hear it go beep in your headset anymore. Sure, you'll fool older systems but if the other guy has the same level of technology you're back to the radar equation and the defending side always has the advantage of their energy being inversely proportional to R² rather than R⁴. If the transmitting radar can detect the bouncing signal the illuminated aircraft sure as heck can.

 

 

That was the thinking in the 1980s, but given modern technology it ain't necessarily so.

 

A radar warning receiver can positively identify a radar pinging it from further away than the radar can make out precisely because of the 1/R^2 1/R^4 mismatch you identify, provided that the RWR knows the transmitting radar's frequency and pulse width.

 

MSA and PESA radars are constrained to a single, or fairly narrow range of frequencies.  AESAs aren't, and furthermore not only can they hop frequencies, they can spread their power over multiple frequencies at once.  And change which frequencies they transmit with each pulse.  And change PRF at will too.  It would be trivial to design the software controlling the frequency hopping to do so in a cryptographically secure manner, so it should be assumed that it does.

 

There are fundamental trade-offs in antenna design which mean that no actual antenna has equal gain over a wide range of frequencies.  There are trade-offs in sensitivity to a peak frequency vs sensitivity over a wide band.  The RWR needs to be able to detect signals from millimeter band radars used in short range SAMs to the L band radars used in long-range detection systems.  There are also trade-offs in coverage vs sensitivity, since antenna gain is a linear function of directivity.  The RWR has to give spherical coverage.

 

So the RWR is necessarily compromised in a number of ways the LPI AESA is not.  Additionally, there's going to be a certain amount of RF noise hitting the RWR.  In order to avoid processing spurious signals, the RWR is going to need a clutter cut-off threshold.  The AESA is going to need to filter out clutter as well, but it can turn down its clutter rejection threshold for the frequencies its broadcasting on at the time its broadcasting on them; the RWR doesn't know exactly what signals it's listening for, so it has no such luxury.

 

So, given the above, it is at least theoretically possible that 1/R^4 is bigger than 1/R^2.  Those who know for sure are not speaking.

 

Also related, someone on SA posted this thing in response to a post about ~aerospace technology~ in acoustic noise cancelling headphones:

 

I'm pretty sure I recall Saab mentioning something like this in connection to the Gripen E, and I think that stuff (well all the EW computer thingies in general) is one of the reason for the new cooling air intake on the base of the tailfin. It wouldn't surprise me if that kind of technology is on all the 4.5th generation fighters within the next ten years or so.

 

 

AIUI, wide-scale active cancellation is too computationally intensive for conventional (4th and 4.5th gen) fighters.  The sheer number of modes in which radar waves can bounce off, or creep around, or interfere on a conventionally-designed aircraft is simply too large for a computer to handle.  I mean, look at the weird shit that radio waves can do:

 

surface_wave_types.jpg

 

Yes, active cancellation works in audio.  In headphones.  Have you seen any active cancellation stands that can muffle out all sound that passes by them in an open area?  Neither have I.  It's that sort of problem.

 

Furthermore, a device that would actively cancel out radar waves has a lot less time to respond with an out of phase waveform than one that's dealing with audio.  Human hearing is hertz to kilohertz.  L-band is a few gigahertz and millimeter wave is a lot more than that.

 

Not counting passive, cheaty bullshit like Salisbury Screens, I would expect active cancellation to be limited to a narrow frequency window and to be of limited effectiveness.  But it would work much better on aircraft that restrict radio reflections to a limited number of modes and directions, i.e. 5th gen.

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I'm pretty damn sure that if you have an AESA yourself your own radar antenna is a significant part of your RWR. Even back in the early 70's radars had passive modes that let you see and record whatever jamming was coming at you (I know for a fact that the AJ 37 had this when it entered service in '71 and I'd be really surprised if everyone else didn't have it too). Today, it'd be really silly to have all this emissions control and then not use your best antenna for listening. It's not like shuffling signals around between different systems is a hard problem these days.

As far as active cancellation goes, I can only reiterate that the dude claims that they could do wide spectrum radio cancellation. Granted, in a lab, but still.

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Yes, the AESA radar is tied into the RWR and probably also the jamming suite on any fifth-gens.  So RWR performance will be better in the frontal sixty degrees.

 

Point still stands; the AESA can use frequency hopping, frequency spreading and pulse width modulation to hide its total signal strength in the RF noise and suffer no loss in sensitivity thanks to matched filtering.  The RWR just has to hope that it's still sensitive enough to tell the spread-out AESA signal apart from this noise.

 

On top of that, even if the RWR does identify that it's been lit up by a radar, the aircraft with the radar still has an advantage.  RWR doesn't have the same resolution as a radar, basically due to antenna design compromises.  Also, it fundamentally can't provide range data the way a radar can, because the radar can time the difference between sending out the pulse and receiving it, and the RWR just knows when it got hit.

 

There was some talk of AN/ALR-94 being able to sling an AMRAAM off in the direction of an RWR contact, and Russian firms were working on something similar.  But this technique would necessarily be less accurate and shorter ranged than properly painting the target with the radar in order to get a firing solution.

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Also, FWIW, the Swedish army textbook "Electronic warfare handbook for the air defense forces: radar and radar technology" from 2004 (an excellent book, it's a pity I don't have time to translate it) briefly discusses stealth/signature reduction and says there are three practical ways to reduce radar returns, namely:

1) shaping (the single most important method)

2) using radar absorbent materials (several techniques are discussed)

3) active interference (the active cancellation thing we're talking about here)

but that only the first two are operational "today" (so in 2004).

So they seem to have viewed it as thing that was not yet practically achievable in 2004 but one that was likely to become so in the near future. I really do wonder if there's a newer edition of this book somewhere...

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Also, FWIW, the Swedish army textbook "Electronic warfare handbook for the air defense forces: radar and radar technology" from 2004 (an excellent book, it's a pity I don't have time to translate it) briefly discusses stealth/signature reduction and says there are three practical ways to reduce radar returns, namely:

1) shaping (the single most important method)

2) using radar absorbent materials (several techniques are discussed)

3) active interference (the active cancellation thing we're talking about here)

but that only the first two are operational "today" (so in 2004).

So they seem to have viewed it as thing that was not yet practically achievable in 2004 but one that was likely to become so in the near future. I really do wonder if there's a newer edition of this book somewhere...

 

 

Active interference is possible, pending improvements in electronics processing speed.  So eventually it will be a useful technique if it isn't already, since Moore's Law exists.

 

But last I'd heard, the processors weren't there yet, and also active cancellation would be much easier to achieve if it were combined with stealth shaping.

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http://breakingdefense.com/2016/09/flight-ops-of-15-f-35as-suspended-due-to-fuel-tank-problem/

 

The US Air Force and Norway announced the temporary suspension of flight operations for 15 F-35As today because of “peeling and crumbling insulation in avionics cooling lines inside the fuel tanks.”

 

The problem, caused by a supplier, was discovered during depot modification of an F-35A and affects a total of 57 aircraft, 42 of them still on the production line.

 

The Air Force statement by Ann Stefanek says 10 planes at Hill AFB, Utah, four at Luke AFB, Ariz. (including the two Norwegian planes), and one at Nellis AFB, Nev. are affected. Of the aircraft still in production, 28 belong to the U.S. and partner nations (three are Norwegian) and 14 are Foreign Military Sales aircraft.

 

The problem “was discovered during depot maintenance on one of the impacted jets where loose insulation was discovered. The issue is confined to one supplier source and one batch of parts,” Mike Rein, Lockheed Martin spokesman, says in a statement.

 

The Joint Program Office provides some more detail, identifying the all-important “root cause.” It was the “use of nonconforming material for the tubing insulation and improper manufacturing processes during fabrication of the cooling lines.” The material, sad to say, “is not compatible with fuel, causing degradation of the insulation and resulting in it falling off the tubing.” I wouldn’t want to be that supplier.

 

The fleet aircraft will probably have go to the depot to fix the problem. The others will be fixed before delivery.

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I'm curious as to how it got that far. Usually the first question you ask in regards to materials that will be in/around fuel tanks is something along the lines of "Can this withstand prolonged exposure to said fuel?" It sounds like somebody knows what material was supposed to be used, but someone along the way decided to use a "nonconforming" material for whatever reason. The TDP was given to you for a reason, follow it and you won't have these problems.

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Active interference is possible, pending improvements in electronics processing speed. So eventually it will be a useful technique if it isn't already, since Moore's Law exists.

But last I'd heard, the processors weren't there yet, and also active cancellation would be much easier to achieve if it were combined with stealth shaping.

As I understand it we're already post Moore, and starting to get uncomfortably close to the end of being able to reasonably expect more than maybe three more node shrinks for CMOS if we're lucky. We might get something good for more progress but that's not the sort of promise it used to be.

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