The design of stealth planes like the F22 is intended to create as small a radar cross section as possible, by avoiding large areas of signal reflection. If whatever is not absorbed is scattered widely, the amount reflecting to any one place is small and that's why stealth works. Using passive signals to track a drone, which is not designed to be stealthy in any way, and track a stealth fighter, which is, is a far easier problem. Not saying its impossible to track stealth airplanes that way, but saying "hey we did it with off the shelf drones so we bet it works for F22s also!" is a wild extrapolation.

Seems like the sort of thing they'd release hoping to worry the US. If they really wanted to know if it worked on F22s they'd test it on their best stealth aircraft and see how much more difficult those are to track than commercial drones. Which they probably did or will do, but they'll never release the results of THAT study!

Stealth aircraft are designed to prevent returning a radar signal in the direction it arrived from, all aircraft have a large radar cross section when viewed form above*, the problem is that when flying at low level below them is an entire planet also bouncing the signal back (Doppler shift radar fixes this).

* the only shape that will get the same radar return from any angle is a sphere.

In a vacuum?

Moo

No no no, it's a sheep in a vaccum. The correct approved El Reg Soviet sound would be "Baaaa...."

Stealth works hard to remove direct reflection. Random scattering still works. An F22 is huge, they're saying that the drone they chose has an equivalent behaviour - who knows, but sufficiently true to look for a grant for further research.

Distributed radar can easily locate a stealth airplane, as can a UHF radar.

As the author suggested, you need each link of a kill chain to work to actually get a military benefit.

So you could scramble a fighter to intercept the UFO you detected with your starlink scattering radar, and then launch heat seeking missiles at it.

Or you could discover that someone spoofed your starlink radar and you'd scrambled planes for nothing,

> As the author suggested, you need each link of a kill chain to work to actually get a military benefit.

A military benefit can be just knowing something is there. A build up of data on routes etc. starts to give intelligence…

With respect to the current situation, with China flying “weather balloons” over the USA, this can simply be China saying to the US we can see the paths your stealth aircraft are taking.

"There may be a UFO"

It's not much miltitary use unless you can find both position and velocity to a relatively high precision.

Needs to be enough to identify it as unnatural (eg going too fast) in a place where there shouldn't be anything according to air traffic control and your own military, quickly enough to be able to scramble your own assets to do "something" about it.

Given that they published, this is unlikely to be able to distinguish birds from planes from toy quadcopters - could just be information warfare, perhaps trying to get the US to waste resources on a dead end.

Or perhaps trying to convince DARPA that it is a dead end...

I'm not going to trust anything released by a Chinese state sponsored agency as it's almost certainly disinformation or of marginal use at best. Also, this work was done in Wuhan, where Covid originated, but the Chinese swore blind for years it never came from there. They have no credibility whatsoever.

As mentioned by others, stealth mainly works by minimizing reflections back to the source, not by absorbing the signals. The angles are calculated to reflect the radar "pings" off in another direction.

Newer submarines such as the German 212 CD are starting to do the same thing for sonar. They have long used acoustic tiles to try to absorb signals, but this is much less effective than reflecting the sonar pings away in another direction (the new submarines of course will use both methods). These newer submarines use a diamond shaped outer hull instead of a cylindrical one conforming to the shape of the pressure hull.

The idea of using separate transmitters and receivers for radar in order to detect stealth planes is not new. This is called bistatic radar (an old idea which has become new again) and has been known about for years and has been tested with things like television and cell phone tower signals. They look for the "holes" in radio signals rather than looking for reflections.

What these Chinese scientists have done is shown a proof of concept that it can be done using Starlink signals. Other satellite constellations of course could be used as well.

I have to disagree with the author of the Reg story however with regards to whether this is useful. If you know that something is there and have a rough location and direction of a target, you can start to bring assets in such as fighters or drones to pin point the location and use other shorter ranged detection means for terminal homing. The big problem has been knowing whether there is anything there to find, and this area of research (and other people are working on the problem as well) tries to address that.

It's like the situation with over the horizon radar. It can't be used for targeting either, but that doesn't mean that it's not extremely useful. This is why many billions of dollars are still being spent on it today.

One other advantage of using satellite signals (or other bistatic radar systems using ambient signals) is that they are much harder to knock out because they don't transmit, they just receive. American air warfare doctrine for example places heavy emphasis on suppressing enemy air defences as the first step in any war, and a big part of this is finding and destroying all radar transmitters when they turn on. Using ambient radio transmissions for air warning throws a wrench into the works in this regards. This is the aspect of bistatic ambient radar that really has people interested.

I was told by someone who was there this was used at the Farnborough Air Show many years ago to allow a ground-to-air missile system to track an F-117.

I do not know if that was just a story and I can find no evidence to support the claim, but it is plausible.

This was a US B2 bomber which was tracked by a British Rapier surface to air missile system as it flew over Farnborough Air Show. They detected and tracked it using their infra-red sensors built into the launch system. Because the missile was command guided it didn't need a radar return signal to home in if it had been launched.

In the version of the story that I read about the Rapier vendor (BAe originally, now MBDA) recorded the tracking incident and were playing it on continuous loop at their sales booth until the US made a big fuss with the air show hosts and had the latter make them stop.

Again, what I heard was that they "cheated" a bit because they knew where to look in the first place and so could point the missile launcher (which had the sensor system built in) in the right direction to pick it up.

And this is why a radar system that can't be used to provide terminal homing signals is still useful. If you can tell that something is there and give a rough location, you can then start working on the problem of find tuning the location using other sensors that have a much narrower field of view.

How is this problem specifically from LEO satellites? I would think that most spaceborn EM radiation is from sources which have been there for eons.

Starlink constellation uses a small set of frequencies and provides a near continuous level of transmission with a reasonably small power fluctuation, it's a far better starting point for backscatter filtering than anything else.

Wasn't there a B-2 downed in Croatia/Serbia the other year becasue it was tracked by disturbances in the force (mobile phone towers) and a fair bit of luck?

I guess if your signal processing is fast enough you might be able to work out a track/target from Starlink scatter in perfect conditions - in practice I think "Eve" will be able to say "oh look it took that route to that target" rather than "it's over there - get it! Quick!".

It was a F-117, and it was always following the same flight path in and out of the area... so good old Mk1 eyeballs and a flak cannon were enough to put it down.

Now the use of telecom towers to track planes has produced several papers, bu so far, officially, nobody has developed a system to use that possibility.

( otherwise there's very good chances it would already be in service in Ukraine... just to make sure it works in a real environment )

upvoted but a minor correction - it was actually an (obsolescent*) surface to air missile system that was used for the shoot down.

[*or perhaps not, given it shot down a F117)

I thought the US lost a stealth bomber over former Yugoslavia because the bomb bay door was open and that made it appear on radar?

https://en.wikipedia.org/wiki/1999_F-117A_shootdown

https://theaviationgeekclub.com/an-in-depth-analysis-of-how-serbs-were-able-to-shoot-down-an-f-117-stealth-fighter-during-operation-allied-force/

The release of this Info comes at a time, when China is starting to release it's own constellation of LEO Comms satellites (i.e. competitors for Starlink).

By making such claims, China might be hoping to whip up a bit of US congressional hysteria, which might lead to investigations and restrictions on Starlink being imposed, or just hampering their nominal operations for a while. Which would naturally give the Chinese competitors a bit of a helping hand...

If this had ANY military significance, this paper would not have seen the light of day, since naturally you absolutely dont tell anyone you can track their stealth jets. That would encourage them to go out and build new and better ones. You would keep that Info a TOP TOP TOP Secret...

The easy way to know where stealth aircraft are is to wait for shit to blow up with nothing in the airspace.