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    Re: Possible GPS Date Rollover problems week of April 6, 2019
    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.
    

       
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