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.
And the Russian system is named (the Russian words for) "Global Navigation Satellite System", but usually only called GLONASS because adding L, O and A is less confusing than having one name for super- and sub-sets in a single category.
The fourth global GNSS constellation is Europe's Galileo. NavIC and QZSS are regional GNSS constellations.
Theory is that Russia is constantly practicing to totally disrupt GPS and GNSS (and the Chinese system) across all of Europe.