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Comment by Sanzig | Hacker News Reader

I'd also be curious about the detection range, even on a sunny day.

Stealth doesn't mean the aircraft is invisible to radar, it just means it has a very low radar cross section, so you can't detect it from very far away. Fly close enough to an air defense radar, it will reflect enough energy to show up, it's not a black hole. The point of stealth is to make it impractical and uneconomical to build an air defense system with a high enough density of expensive high performance radars to reliably detect the aircraft.

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The video says up to 100km. With a jet moving at mach-whatever and air-to-surface missiles they can launch from 200+km out, not super useful in practice, even if it worked at night or on cloudy days.

Ultimately this is an economic argument. With about $10k you can buy a few dozen machine vision cameras [I would say "webcams" if I knew less about webcam compression], a PC with mobile modem, and a self-contained solar power supply. For $10M you can buy a thousand of these. A thousand of these evenly distributed within a few hundred kilometers of your country's borders are going to add dramatic capability to your air defense network compared to going from 5x $10M radar systems to 6x $10M radar systems. The key bit is that $10k costs far, far less than a single strike missile to take out one of these optical detection sites.

A full Patriot battery is $1100M, with the durable radar and command components being more like $400M.

Add another $10M and build passive radars from consumer stuff that listens for ruccus in telecom and television fields and you have a pretty annoying defensive baseline.

few old iphones or android smarthphones would do the trick even better - they have much better cameras than webcam, old iphones can even record at 240fps. NPU, GPU, LTE, GPS, battery, IMU, stereo microphones also already included in one package.

not really as most modern airborne weapons platforms operate bvr, even if they were on the horizon, and your array of cameras were operating in optimal conditions there is a still a hard limit on the effectiveness of such a solution.

For offensive work, yes. If you control the ground, though, and are policing a defensive perimeter against air attacks on targets in the interior of your territory, you can make and distribute the camera stations cheaply enough that it doesn't make sense destroying them.

Could the advantage be that a military monitoring installation of cameras is less detectable than a high-frequency radar monitoring installation? My understanding is that active radars are easily detectable, but perhaps cameras could be less so and that advantage could allow them to be deployed closer and might require less protection themselves.

Yup, that's certainly one. I see this technique as simply one more tool in the toolbox. Air defense (and really, all of warfare) is not a single "this thing is better than the rest" but a system of things that work in conjunction with one another. This system has advantages (passive, cheap, portable) and disadvantages (short range, clear weather only). It's good and useful work, and could conceivably be part of a larger system.

Most stealth aircraft are only stealthy against the higher frequency radars.

And only the higher frequency radars are really useful for interception or weapons targeting. The lower frequency radars are good at long-range detection but they're far less precise.

Early stealth aircraft designs like the F-117 and B-2 were optimized for signature reduction in the frequency bands most typically used by air defense and fighter radar sets. Newer designs like the B-21 and F-47 supposedly have "broadband stealth" which reduces radar cross section across a broader range of radar bands but details are classified.

The "stealth aircraft hate this one weird trick" conversation also has to contend with jamming, because many of the techniques that work great at spotting stealth aircraft in peacetime are especially vulnerable to jamming. This makes them far less useful in an actual conflict.

The Saab Gripen is said to be particularly effective in this regard.

I'm pleased at the discussion in this chain of replies, as it illustrates the cat-and-mouse game stealth (low observability?) is. Stealth never was a perfect defense, as it's detractors claim. It forces the adversary to make tradeoffs, such as increasing the costs needed to detect such craft, which can then be exploited for gain.

Jamming is a function of power and there are few radars that put out more power than the low frequency surveillance radars. Duga was colocated with the chernobyl nuclear power plant.

It's the tailless triangle shape. F117 used facets and coatings.

Insert: energy harvesting skin provides 2 microwatts of power

Aren't some folks just watching the reflection of cell phone signals? Why bother with an expensive radar system when the cell phone system is flooding the sky with radiation anyway?

Depending on the war, you might not have cell phone (basestation) signals everywhere during actual fighting, relying on that seems a bit limiting.

Sure because at end of day, radar is all about detecting bouncing radio waves.

However, it's accuracy of detection that changes the battlefield and my guess is detecting disturbed cellular signals gives very low detection chance/range.

Also, if enemy thought it was problematic, hit cellular tower with missile is extremely easy.

Cells are highly directional, and should ideally not be installed facing the sky. Add stealth coatings to the mix, and your return signal may not be enough to detect. Radars use high power emitters.

https://www.rcrwireless.com/wp-content/uploads/2023/08/Pictu...

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