US satellite jammer is set for delivery as flaws are fixed
50 comments
·October 25, 2024echoangle
Is there some more info on what exactly this system is jamming? Radar satellites? It probably can’t prevent optical images and downlinking of collected data to enemy ground stations.
Edit: according to this ( https://www.dailymail.co.uk/sciencetech/article-14001079/amp... ), it jams enemy communication which is relayed over satellites. I imagine this only works if the receiving antenna on the satellite isn’t highly directional enough to only pick up signals where enemy troops are known to be. If the satellite has a phased array, the origin of the signal could be filtered very fine grained as far as I know and this kind of jamming could be removed (unless it is so strong that it completely saturates the amplifiers of the receiver?).
moandcompany
Communication satellites generally need to have multiple antennas to provide spanning coverage over large geographic areas, which are divided up into coverage cells; some of the antennas may be phased array antennas; antennas and their associated coverage "beams" are generally steerable to some degree, electronically for phased array, and/or mechanically via physical gimbal mechanisms. In some or most cases, communication signals are non-viable without focused coverage because the signal strength would otherwise be insufficient.
Received signal strength, from the point of view of a terrestrial satellite communications terminal on the ground/airborne/maritime can also vary based on where the terminal is located within the footprint of a communication satellite's coverage beam; it's typically strongest at the center of a beam.
The most primitive conceptual model for a communications satellite is often described as a "bent pipe," where signals transmitted up to a satellite from the ground are relayed as-received by the satellite back down to terrestrial receivers. In the linked article, the diagram reflects a concept such that: if a "jammer" can interfere with the transmitted signal to the satellite in a manner that the satellite cannot discern the true signal from noise contributed by the "jammer," what is relayed back down to terrestrial receivers by the satellite is "drowned out" because the relayed signal is now a combination of the true signal and sufficiently more noise contributed by the jammer rendering the communications channel and any signals over that channel non-viable (i.e. "jammed").
echoangle
> Received signal strength, from the point of view of a terrestrial satellite communications terminal on the ground/airborne/maritime can also vary based on where the terminal is located within the footprint of a communication satellite's coverage beam; it's typically strongest at the center of a beam.
That’s why I was asking, the jammer would have to be very strong to overwhelm a „real“ signal which is located in the main lobe when the jammer is outside.
moandcompany
>That’s why I was asking, the jammer would have to be very strong to overwhelm a "real“ signal which is located in the main lobe when the jammer is outside.
The mobile jammer in the article's scenario is transmitting toward the satellite, not the terrestrial terminals on the ground.
Imagine in the primitive example case that the "real" signal transmission must also be coming from a terrestrial terminal as well. The real terrestrial terminal is likely be similar in size to the mobile jammer, and subject to the same kinds of constraints as the jammer. However, the jammer doesn't have to consider much about the quality of its radiated energy at the target frequencies. Let's also assume that that both the real transmission terminal and the jammer can emit the same amount of energy.
The distance between both the real transmission terminal(s) and the jammer to the communications satellite, for all practical purposes, is roughly the same.
From the primitive example communications satellite's perspective, it will see/hear both the real signal and an equally "loud" signal (noise) at the same frequencies. When the communications satellite relays or retransmits what it hears to the receiving terrestrial terminals, it will be the combination of what the satellite saw/heard.
Instead of the "bent pipe" imagine another primitive example where the communications satellite is an optical mirror, and the "real" signal comes from a light source on the ground pointed at the satellite. The "real" signal could be represented using different modulations of that light in brightness, frequency/wavelength, as well as temporal pulses. Terrestrial receivers decode the "real" signal based on the flashes of light it observes from the mirror. The jammer in this scenario is another light source pointed at the same mirror.
Terrestrial, ground-based jammers are not the only type of potential jammer in a satellite communications system's operational scenarios. In the prior example ground-based jammers look upward to jam the satellite. You can also imagine scenarios where airborne jammers are possible, which look downward to jam receiving terrestrial terminals.
A ground-based jammer versus an airborne jammer would have a few differences. The ground-based jammer mostly needs to consider a fairly well-known location of the communications satellite, as the satellite can be easily observed, and its future positions can be calculated using ephemeris data, for targeting. An airborne jammer would have to deal with the issue that it has a lower field of view than the satellite beam's footprint and needs to have more specification information about the location of terrestrial receiving terminals to apply its own area of effect, which would be smaller than the satellite's beam. However, the effective distance between the airborne jammer and terrestrial terminals will be orders of magnitude lower than the communications satellite and terrestrial terminals. Power transmission capacity is a constraint for all terminals, satellites, etc, and an airborne jammer's ability to apply power will be more effective than satellites due to distance, but the airborne jammer must be more selective on where to apply (i.e. target) that power.
One jammer could be used to affect the transmission signal, but it would likely take many jammers to target receiving terminals when there are many geographically dispersed terminals.
2OEH8eoCRo0
Noob antenna question: in a phased array is most transmit energy lost to destructive interference?
I thought that the beam was just the region where the waves didn't destructively interfere
JumpCrisscross
> in a phased array is most transmit energy lost to destructive interference?
No. Phased-array antennae can be up to 90% efficient [1]. You aren't losing energy to destructive interference so much as channeling it to the constructive modes. (Totally physically inaccurate, but I think analogously correct.)
[1] https://www.mwrf.com/technologies/embedded/systems/article/2...
grayfaced
Low gain where there is destructive interference and high gain where there is constructive interference. That is the feature. Same amount of energy is radiated, it is just amplified in the high-gain main lobe.
A low gain direction is not the same as no signal though. With enough power you can overpower the main lobe signal.
sidewndr46
A phased array can have its phase altered to be steerable. That doesn't work if you overwhelm the receiver to the point it becomes a non-linear device.
MegaDeKay
Yeah, but it does take a lot more power as you point out. Just like you can use the phased array to form a beam toward a particular location of a particular size, you can also do the opposite and create deliberately low gain toward the jammer. So then you need enough jammer power to overwhelm the LNAs on the individual elements, each of which have relatively low gain.
sidewndr46
no, it doesn't work that way at all. The receive side of a communication satellite would be multiple antennas each connected to its own receivers. The receiver all use a common clock source to perform demodulation (which is a bunch of steps usually, but whatever). The result of each receiver is summed, the result signal is transmitted by another transmitter connected to a different antenna on a different frequency. Phase difference between the receivers is used to steer the array. How the phase difference is created varies. But if you overwhelm just one receiver it basically just injects noise into the entire process. So you wind up summing noise with all the other signals, which destroys the signal to noise ratio of the transmitted signal
now if the control station can switch one receiver off to a dummy load, instead of to an antenna that might be useful. Whether or not military comm satellites can do that is most definitely classified.
fasteddie31003
I bet it would jam synthetic aperture radars
aurizon
Most modern command/control systems are what is called 'frequency agile' https://en.wikipedia.org/wiki/Frequency_agility#:~:text=Freq.... and so a C&C system operates cross a wide band, and each system has a series of one time tables that says 'next hop' and the transmit and receive communications - or it random hops, with each one telling 'next'. Small drones can not carry the computational power to do this. Often the higher power base does all this and tells the drone/missile 'next' Frequency agility, coupled with directional agility(phased array) make it harder. Drone systems usually depend on higher power frequency hopping to saturate a range of frequencies and hope for the duration of the desensitising effect where the lower power and computational power of the drone to insert ambiguity into the bidirectional C&C signals and hope the drone settles down or goes home. It is complex, but as the drone get further away from the C&C it becomes easier to disrupt. A drone can fly in a cruise mode and when it detected interference - often with sync bars on the screen, instruct the drone to switch into a less jammable frequency (but uses more battery power- the scarce resource in a drone) as it gets closer to the target where more jamming power is expended. I expect low power ARM systems will help in this.
HarryHirsch
Wouldn't such equipment attract anti-radiation weaponry very quickly? Combat practice with anti-aircraft battery is to light radar up for 30 seconds at most and then relocate immediately, because anything more will attract counter-battery fire.
amelius
What mechanism is this using?
darquomiahw
I'd imagine a parabolic dish that points at the satellite, driven by something powerful like a klystron. With a highly directional antenna and high power one should be able to saturate the satellite receiver.
Jtsummers
That's what L3's published images look like. A dish on a trailer that can be moved to wherever it's needed. It's an antenna that's producing (mostly) high-powered noise while pointed at a target satellite. Probably configurable like an ordinary antenna to make it mission specific and take advantage of known weaknesses in the target system.
lysace
https://en.wikipedia.org/wiki/Klystron
Early 1900s electronic devices/components have the best names.
greenavocado
I'll take "What are loitering munitions?" for $100, Alex
Arrath
I feel like we're due for a proliferation of anti radiation munitions.
aaron695
[dead]
sharpshadow
Uhm are they serious!? Jammers are forbidden by most countries and they find it okay to put that into space as a satellite. Honestly if the scenario they describe when it comes to use it will be a target immediately and shot down just causing more debris. Space should be kept weapon free for the sake of humanity.
ceejayoz
> Jammers are forbidden by most countries and they find it okay to put that into space as a satellite.
You'll find such forbidding tends to exempt the countries themselves. Every military on the planet uses jammers.
I can't collect taxes, but they can. I can't put someone in jail, but they can. I can't negotiate with foreign powers, but they can.
Brybry
> I can't negotiate with foreign powers
As an aside, I think this one is a maybe (in the US). Weirdly in over 200 years there's only been two indictments under the Logan Act and no convictions. [1]
[1] https://www.reuters.com/article/us-usa-trump-russia-un/flynn...
Etheryte
Shooting other people is also forbidden in most countries, but militaries of said countries are still allowed to do it e.g. when they're at war. This is the same, but for satellite communications.
tullianus
The jammer under discussion is not a satellite. It is a ground-based system that jams satellites. Did you read the article? There's even a photo of the system right at the top.
sharpshadow
Damn I’m sorry.. the picture was blurry on the device I used since no JS and it was just the free part of the whole article. I was sloppy at the end of the workday and the weekend ahead.
Probably also biased towards a satellite with jammers.
JumpCrisscross
> shot down just causing more debris
Yes, wars create debris. In this case, on the ground.
grayfaced
Jammers are only illegal in the civilian legal context. I'm not aware of anything that makes jammers inherently illegal by broader law of armed conflict. Necessity and proportionality comes into play. Targeted jamming of military communications would certainly be allowed. Jamming of dual-use satellites becomes more nuanced.
petre
> Jammers are forbidden by most countries
Russia is jamming their Western neighbours' GPS. I can't wait for US microwave weapons that fry their satellites.
tullianus
The current slate of Russian GPS jamming is not being done by satellites.
krisoft
Same with this system. It is terestrial with wheels.
petre
They have satellites of their own. Since it's more expensive to launch, put them into orbit and operate them, I'm sure they'll reach some sort of "mutually beneficial" agreement, like we promise not to screw with yours if you won't mess with ours.
https://archive.is/0fjW1