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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Possible GPS Date Rollover problems week of April 6, 2019
From: Paul Hirose
Date: 2019 Mar 30, 14:41 -0700
From: Paul Hirose
Date: 2019 Mar 30, 14:41 -0700
The origin of the GPS time scale is 1980 January 6 00:00:00 UTC = 00:00:19 TAI = Julian date 2 444 244.5 + 19s TAI. A week number rollover occurs every 1024 weeks, and this will be the second rollover in GPS history, so add 2 * 7 * 1024 days to obtain JD 2 458 580.5 + 19s TAI = 2019 April 7 00:00:19 TAI. Until the next leap second, UTC is 37s behind TAI. Therefore, April 7 00:00:19 TAI - 37s = April 6 23:59:42 UTC. That's when the rollover occurs. Today I tested a 1994 Magellan Trailblazer, one of the first affordable GPS receivers. It was unable to produce a position, even after more that 30 minutes. The date it displays is in August 1999, but its UTC time of day is only a few seconds off. 1999-08-14 20:56:08 = displayed UTC 0 = cycle number 1022 = GPS week 593781.00 seconds 2019-03-30 20:56:00 = correct UTC 1 = cycle number 1022 = GPS week 593778.00 seconds "Cycle number" is the number of whole 1024-week cycles of GPS time that have elapsed. The week numbers are identical and the seconds since the beginning of the GPS week differ by only 3.
