Comment by h3half

My understanding was that each satellite broadcasts a coarse ephemeris for the whole network, and that that “almanac” isn’t accurate for very long (on the order of weeks). Without uploads to the satellites, those almanacs will go stale.

I don’t think the almanacs are necessary for the system to work, in theory. But I believe they’re commonly used by receivers to narrow down the range of possibilities when trying to find a PRN match for a signal they’re getting.

(I’ve dealt with GPS and similar navigation signals for work but am not an expert, this is just the impression I’ve gotten over a few years)