Also keep a close eye on the Opensource SatDump project. That's a group of (mostly ham, but not all of them) radio enthusiasts that are listening to all kind of science satellites. They managed to decode many of them.
They are far far beyond the old 137MHz analog NOAA stuff. Collecting crazy broadband from S- or X-band is no challenge for them.
I wouldn't say it's mostly HAMs. More that it's a small community of largely European teenagers and 20 somethings. I say that as someone who found their way into the hobby back during covid and now have up and running L, S, and X band setups.
Twitter, Derek's SGC's discord (https://discord.gg/7fFFzNsPEF), and Alan's Matrix server are the three main places to find imagery. That and people's own personal web sites. Here's mine.
https://geostation.io/
Please don't criticize my site too much, I've not updated it for ages and historically I used it as a place to dump output from my geostationary satellite stations.
And I guess the other thing to mention is that x band data often adds up real quick, so it's nowhere near as prevalent in full resolution online. I'm basically surrounded by forest and only get sync on Chinese LEO sats at maybe 35°+ north and then lose sync due to the forest at ~30° elevation south. My resulting true color composites are routinely 400-500MB.
Someone with clear LoS to either horizon can easily produce composites that are over 1GB per image.
> Galileo was the ugly duckling for a very long time - but it turned into a shining one after it aged a bit.
Yeah, for some time I was also in the camp of "why we need our own expansive service". But the current development has shown, that it was a wise desicion to have our own system.
BTW: thanks for updating on some other details. I never followed up really, it was from the initial plans, that I was told there should be comercial service, that should pay. Also that for some emergency services there is a very limited possibility to have a back channel.
It has optional cryptographic signatures of the navigation message, i.e. the data indicating position of satellites.
Spoofing generally works not by altering the navigation message, but by altering the timing of arriving signals. I'd recommend this video for a publicly-available overview of the techniques: https://www.youtube.com/watch?v=sAjWJbZOq6I
A) you keep on using the word "almanac". That term only refers to the imprecise information about all satellites that every satellite broadcasts, mostly to improve TTFF. The actual position used for navigation is called "ephemeris", and each satellite only broadcasts its own.
B) none of that other stuff in the navigation message changes the pseudorange, which is what spoofers mess with. For a networking analogy - pseudoranges are calculated based on layer 1/2 properties of the network. (Specifically the code phase and Doppler shift.) Navigation messages are layer 7 information passed on top of that physical layer. You can change the timing and frequency characteristics of the PRN code without touching a single bit of the navigation message.)
The G/NAV message (note the G - government) is for a separate service - not OSNMA - where not only is the navigation message encrypted, but the PRN code is also encrypted (symmetrically, so it can't be done for the mass market or even untrusted commercial customers).
In other comments to this link people are describing GPS according to my mental model, which is hard to combine with cryptography making it un-spoofable.
If someone can re-broadcast the keystream and control the latency I perceive as a receiver, how would me checking that the MAC is correct help?
