One person's experience on GPS rollovergreenspun.com : LUSENET : TimeBomb 2000 (Y2000) : One Thread
My son sent me his account of what happened with his GPS rig at the August rollover.My GPS is finally out of purgatory. There was a 4 week window after the GPS rollover where my GPS had to be cold-booted each time it was powered up or it wouldn't be able to find the satellites it was looking for. I could have fixed this with a software upgrade if I was willing to spring for the communications cable so I could connect the GPS to my computer and squirt in the upgraded software. Now that the four weeks is up I boot the GPS normally and it starts right up. I suspect that my version of the software maintains a cache of where/when it was going back 4 weeks -- it uses the time delta to precompute where it expects to find satellites. Until the pre-rollover stuff gets purged out of the cache, the predicted satellite locations it computes are bogus.
I kept the GPS on the whole day when the GPS rollover occurred-- nothing happened. The GPS just kept on ticking, as it were. Shortly after the rollover, I even shut it down for a bit and re-started. It started up just fine, probably because the satellites hadn't moved appreciably -- the next day when I tried to start it, it coudn't find a damned thing until I cold-booted it, taking about 20-40 minutes to 'scan' the sky and matching what it was finding with its internal database.
-- Tom Carey (firstname.lastname@example.org), October 06, 1999
Our Garmin 180 didn't have any trouble at all, on the rollover date or any time thereafter. We use it navigationally in the Gulf of Mexico, and it always found seven to eight satellites, no problem. Must have been eating it's Wheaties, or something.
-- Elskon (email@example.com), October 07, 1999.
Your analysis is fairly correct. There is an internal "almanac" which allows a calculation of satellite position based on date/time (week counter). See the article in Aviation Week & Space Technology, Oct 4, 1999 for more complete info. I will post this in a separate thread above for everyone.
-- RDH (firstname.lastname@example.org), October 07, 1999.