They don't attempt to jam, the frequency is just little bit off to minimize damage and it's very short time. They just test the system to verify that it works.

What this reveals: Russian early warning satellite constellation has also GNSS jammers they test periodically. They can jam whole continent from single satellite. They have six satellites in Molniya orbits.

Anyone have a good source to read up on the current state of the art for daytime celestial navigation? Maybe there isn't too much in the public domain, because things like GPS work so well. But I'd guess that since you can't easily artificially jam celestial navigation there would be military research on this. But I suppose clouds also limit the practicality as well.

https://www.scientificamerican.com/article/how-to-see-stars-...