I Found The US Nuclear Detection System In Space

Added: 2026-05-28

[00:00:00]Hello and welcome back to the Save it for Parts channel. Recently, I was taking a look at some satellites with the array of antennas up here on my garage, as you do, and I came across something kind of unexpected. Recently, I've been playing around with the Discovery dish and motorized Discovery drive. These are hobbyist level equipment sold by KrakenRF, and they can do quite a bit of stuff, and I've been having a lot of fun with these. I actually started writing a computer program to do some room entry radio astronomy with the Discovery drive using a variety of antennas. The Discovery dish has interchangeable feeds or center elements tuned to different frequencies, and one that I was playing around with is tuned for 1420 MHz, which is a common radio astronomy frequency, and that's supposed to be kind of a quiet frequency that uh really only detects natural phenomenon out in space. If there are international laws against using 1420 MHz for anything else. Now, it turns out there are some human-made radio signals out in space that are close to this frequency. Uh they're exactly at 1420 MHz, but they are actually close enough to cause some problems for radio astronomers. Now, because there are no artificial signals at 1420 MHz, it can be sort of hard to test my setup. I've been using the same software and the same dish with different feeds to do image maps or heat maps of different satellites in the sky. For example, here are some geostationary weather satellites. Here's a geostationary communication satellite, and here are some medium Earth orbit navigation satellites like GPS, the Russian GLONASS system, and the Chinese BeiDou system.

[00:01:34]And GPS did give me an idea for something I could test here because there is a L3 frequency that uses uh 1380 MHz or thereabouts, which is somewhat close, and I thought might be within the frequency range of this uh antenna feed. Yeah, I'm really I'm really not seeing anything here. We're getting a little bit of random interference, and uh we are finally getting some kind of signal up at the top, which I guess could be a satellite going through, and it has kind of affected the entire range of my preview, but I'm I'm not 100% sure what it is that I'm seeing. So, I ran a scan on that L3 frequency, just expecting to see the same GPS satellites, and I actually didn't see much except for some kind of strong blips of data uh towards the end of the scan, and I thought, "Well, that's weird." So, I ran the scan again, and I didn't see anything. No just no transmissions at all. So, I was thinking, "Well, okay, maybe GPS doesn't use this L3 frequency."

[00:02:30]I did some research, and it turns out that the main purpose of the L3 frequency is for nuclear weapons detection, because GPS satellites are also uh arms control satellites, and they look for nuclear detonations. So, when they detect one, they transmit to all of their friends. Each GPS satellite will tell all the other GPS satellites, "Hey, I just saw a nuke go off somewhere." Or what I think was a nuke go off. And they'd pick up other things as well. They pick up X-ray emissions from space. They pick up uh natural processes. They pick up things that aren't nuclear weapons. But, apparently the L3 frequency is kind of used on demand for this reporting system and isn't really used for anything else. So, the only time that I'll see data on L3 on this particular frequency is when the GPS satellites think they've seen a nuke go off. So, that's kind of cool. I just happened to catch one. Actually, two satellites. I happened to catch two satellites transmitting. And you can actually see the first one transmitted on the left, and the second one was transmitting, and by the time the dish swept back to that first satellite on the left, it was no longer transmitting.

[00:03:37]So, these are just short bursts of data.

[00:03:39]And who knows which satellite originally thought it detected something, but it was bouncing around the entire GPS network when I was happening to scan across. So, that was just really cool to to happen to catch that. When I did the second scan of this frequency, I saw nothing. And if I had only done one scan and seen nothing, I probably wouldn't have bothered to look this up. I just would have thought to myself, "Okay, well, they're not using that frequency."

[00:04:02]I have to say I'm learning a lot more about the GPS network by doing these scans than I ever realized. I think I had heard somewhere that they did nuclear detection, but I didn't realize they used that L3 frequency for it. So, yeah, I am learning right as I'm doing this project. The standard GPS frequency shows these very bright dots where the satellites are located. And since these are in a medium Earth orbit, you can actually see a little bit of motion blur because the satellites are moving at about the same speed that my dish is scanning. My dish takes an hour or more to scan over a segment of sky. So, it's kind of like a long exposure on a camera, and a moving object like a medium Earth orbit satellite shows up as kind of a smear, much like a moving object shows up as a a smeared image in a long camera exposure. I have a whole separate video on this experiment if you want to know more about the process and the software. Let's show you what this looks like to do the scan. I am running my custom code here, this DD scan Python script. I'm giving it a range of azimuth and elevation. That's kind of the XY coordinates in the sky. I'm giving it a frequency, and then I'm telling it to turn on the bias T, which powers the uh powered amplifier inside of the dish feed. First off, the dish has to move over to the uh start position, so that's what it's doing now. So, my dish is essentially doing a sweep scan of the sky. It is panning across in that azimuth range, and then it increments up 1° in elevation, scans back across. You can see here in the preview image, each pixel is one X and Y coordinate pair is one degree position in the sky. So, as the dish scans across, it is filling in each pixel in the heat map with the signal strength, with the amount of radio signal is picking up at that coordinate. And this heat map will kind of dynamically change as it gets more or less signal. It will It will kind of attune itself to the minimum and maximum range of the signals seen during the scans. For my radio, I'm using the RTL-SDR Blog V4 from rtlsdr.com.

[00:06:08]You can find these on Amazon as well.

[00:06:09]I'll put a link down in the description.

[00:06:11]I found this SDR to be the easiest one to interface with Python. I can call a Python library and use the radio right within my code. So, that's the one I'm working with. So far, we've been looking at these signals just in a spatial dimension, just where are the signals in the sky? But, I'd also like to see what those signals look like on the radio spectrum. What do they look like on an SDR waterfall plot? Kind of the standard way to look at your software-defined radio signals. Now, this is going to be a little bit challenging because these are moving satellites and the signal is intermittent. It's not always coming down from particular satellite. Each one is just doing a test now and then. I believe they do retransmit between each other when there is an actual detection.

[00:06:57]But, if they're just doing test messages, I think they're just one at a time. Sometimes, apparently, they will do week-long tests where each satellite will transmit for several minutes at a time. But, they have to coordinate that with radio astronomers because again, this interferes with science. So, my approach to try to get one signal at some point is to just aim the dish south at about 45°. Then, we have a chance of catching several satellites during the course of an hour. And I'm just going to listen to that frequency, just record a baseband on the SDR program. I'm running SDR++ on Linux. This is the interface that I most often use for my software-defined radios.

[00:07:36]We're going to turn on the bias T. So, again, that powers the amplifier filter unit that's on the Discovery dish.

[00:07:43]So, you can immediately see the signal got better once that uh amplifier was turned on. We do get this noise in the middle that's pretty standard that we're getting um DC noise. We're getting interference from our own system. Okay, we actually did get something, I think, um that was wider than that 1 MHz bandwidth. So, I have upped the bandwidth back to uh 2.56 MHz. We're going to try this again. Now, I didn't find a ton of information online on what this signal actually looks like or how it's structured, which isn't surprising because this is a military nuclear detection signal. They're not just going to publish the standards for it.

[00:08:18]Although, they did publish a lot of the standards for the older uh nuclear detection system or Nudet from uh some of the first GPS satellites. And there is some documentation online for that going into a lot of detail on uh signal standards, on encoding, on Oh, wow.

[00:08:35]Okay, I just saw this thing again. Oh, we just got something while I was babbling away.

[00:08:40]We got a burst of data here uh centered around that 1381.05 MHz.

[00:08:46]So, I think this is our nuclear detection message coming from one of the GPS satellites. As I started to say earlier, there is a lot of documentation on the early version of this system. Uh so, you can see the uh signal standards.

[00:08:58]You can see the encoding. You can see a lot of the information about how some of the earlier uh nuclear detection system worked. And there's a ton of math in some of these papers. There's a ton of stuff about, well, if we get uh this velocity of the neutrons and the gamma rays and we get uh this from the visible light, and they, you know, they have some false positives. Uh we've heard of stories from Russian satellites where they saw sunlight reflecting off of an uh icy cloud layer, and they flagged that as a nuclear detection. And they actually set off some alarms saying, "Hey, the the Americans are attacking us. They've launched the missiles." And yeah, it turned out to be a false alarm.

[00:09:36]So, these satellite systems are not perfect. A precursor system called Vela picked up a mysterious nuclear test back in 1979, and it's still kind of unclear who set this off. It's widely considered to be either Israel or South Africa or both, but the 1970s were such a crazy time that you'd have countries just nuking the ocean and then never admitting to doing it. And the nuclear detection systems are always evolving.

[00:09:59]There are new ones going up every time a new GPS satellite is launched, it has an updated sensor suite, um updated detection systems, and then they're always updating the computers on the back end. So, yeah, it's it's an evolving system, and it's just really interesting. While I was babbling away there, I missed another little blip of data. I was always terrible at math in school, and I was never really good at computer programming, even though I went to school for computer science.

[00:10:25]Uh so, it might seem ironic that I got into a field where there is a lot of math and computer programming, uh but radio stuff, especially software-defined radio stuff, is super forgiving. It is It is very easy to get started in very basic stuff, and there are a million directions you can go in it. You don't necessarily need to know the neutron velocity muxed with the GPS time coordinates to uh to look at a signal and find out a little bit about it. And you don't necessarily need to know how to program to be able to to use somebody's program online and um run it on your own system and do something interesting. And I put all my code online, so if you want to uh use my scanning script for Discovery Drive, it's on GitHub. I'll put links to that down below as well.

[00:11:08]Um but yeah, I I like I said, I learn a lot uh from doing this. I learn a lot more than I did in school by just playing around with stuff that I'm actually interested in because the examples in school are always kind of like, who cares? They're boring. Uh but this stuff is interesting. So, uh this really motivates me to learn more, and if I don't understand a particular aspect of it, well, I can go in some other direction. I can look at a weather satellite signal or I can look at something else because yeah, there are kind of infinite directions you can go with this stuff. All right, I think we're seeing it again. Yes, I think that was a nuclear detection system message from the GPS satellites. Let's compare this L3 signal to regular old GPS on L1, the navigation signal. To do that, we're going to swap out the feed on the Discovery dish since the L1 signal is up around 1575 MHz.

[00:12:00]Uh it's at a higher frequency than this one is really tuned for, so we're going to move up. Now, a few people have asked about the strength of the GPS signals in relation to the noise floor. Basically, the kind of background noise, the cosmic background and Earth background noise is what you call the noise floor, kind of the minimum uh signal on your SDR. And GPS signals are supposedly below that.

[00:12:23]They were designed to be a little bit below that in the old days to be kind of hard for uh foreigners to use, hard for non-military users to access.

[00:12:34]And then in the 1980s when they started making GPS available to the public, um well, basically, you get a filter amplifier unit that filters out other frequencies, amplifies the particular frequency that you want, and that helps boost a signal from potentially at or below the noise floor up to something a little more usable and a little more visible uh to human eyes on a software-defined radio screen. This one thing I really like about the Discovery dish system is it's really easy to switch to a different frequency. You don't have to uh change major stuff. You just pop out the the center arm here and you pop in a new one. So, that's what a regular old GPS navigation signal looks like on the L1 frequency, 1575.42.

[00:13:18]Yeah, it's definitely recognizable as a signal. It's a little bit choppy, a little bit noisy. We're not necessarily pointed directly at a GPS satellite right now. I just have the dish pointed kind of randomly towards the south and if a satellite isn't in direct line of the dish, then I'm just getting a signal from off to the side somewhere. I did move the dish around a little bit and just randomly stumbled across a GPS satellite. So, here's a much stronger signal. Here is GPS L1 with the dish aimed a little bit more precisely, definitely well above the noise floor, especially with a parabolic dish with a filter amplifier low noise amplifier combo that we have in the discovery 1550 MHz feeds. I don't know what the actual data structure of this is. I don't know how close the nuclear detection signal is to the actual GPS signal. I would imagine they're pretty different because they're using they're doing different things and some radio astronomers have actually looked at a little bit more of the signal characteristics of that L3 signal because they're trying to avoid this signal. They're trying to figure out how to filter it out. And so, they're trying to reverse engineer it a little bit to figure out how to better block it from their scientific instruments. So, I think it was really cool to randomly stumble across the space-based nuclear detection system. I was not looking for that to start with. I was not expecting to see that. In fact, I didn't even I kind of had heard about it, but I didn't really know that it was on that frequency. I didn't know what it would look like. So, I really knew nothing about this going into it and I know a little bit more now. I still don't know how to decode any of that. I can't get any data out of it, which is kind of typical for a lot of my satellite projects with unknown, especially military-based systems. You can see that there's a signal there, but somebody like me can't necessarily get much out of it. Maybe there are some experts out there who could do more with it, who could get something interesting, but maybe somebody will say something in the comments. I will look forward to that.

[00:15:15]If you enjoyed this video, please consider supporting me on Patreon or YouTube membership, which really helps out the channel. And then if you want to see other projects like this, I have a whole playlist of satellite and radio topics, so you can go back and check that out. And then of course you can stay tuned for our future adventures in the world of software defined radio and amateur satellite experiments. Thank you to everyone out there for watching, and we'll see you next time.