NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Paul Hirose
Date: 2025 Dec 22, 17:36 -0800
The report on the October 2025 meeting of the CCTF (Consultative Committee for Time and Frequency) mentions the 2022 CGPM resolution that says, "the maximum value for the difference (UT1-UTC) will be increased in, or before, 2035."
Earth may force action before 2035 to avoid a negative leap second, which according to one authority has about 30% probability in the next 10 years. The world is not ready for a negative leap second! I believe my Lunar 4.4 program will have no trouble, but I haven't tested that.
In navigation, "When UT1-UTC is larger than 1 second, it will be very important to disseminate this value to all the users with reliability, accuracy, robustness, large availability and coverage."
• GPS can accept ± 63 s (modernized one should be ±127 s, already implemented in some satellites)
• GLONASS has been modernized to accept ± 255 s (11/24 satellites)
• Beidou can accept ± 63 s
• Galileo is not transmitting UT1-UTC
What about radio time broadcasts? "ITU-R Rec 460, containing the code for broadcasting UT1-UTC by radio emitting stations, has to be updated with UT1-UTC > 1s." And, "11 countries have radio stations in operations yet, only 5 transmit DUT1 = UT1-UTC. All plan to stop this service, only Russia plans to maintain it on 3 radio stations that will be updated accordingly to the ITU R code update (in progress)."
The first half of the report discusses the redefinition of the SI second, which doesn't directly affect navigation.
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Paul Hirose
sofajpl.com
