Re: [LEAPSECS] Introduction of long term scheduling

From: Steve Allen <sla_at_UCOLICK.ORG>
Date: Fri, 12 Jan 2007 11:26:53 -0800

On Fri 2007-01-12T18:35:55 +0000, Tony Finch hath writ:
> According to the slides linked from Dave Mills's "Timekeeping in the
> Interplanetary Internet" page, they are planning to sync Mars time to UTC.

Neverminding the variations on Mars with its rather more eccentric
orbit, the deviations from uniformity of rate of time on earth alone
create an annual variation of almost 2 ms between TT and TDB. This is
also ignoring variations in time signal propagation through the solar
wind when Mars is near superior conjunction.

To some applications 2 ms in a year is nothing. From an engineering
standpoint a variation of 2 ms in a year on Mars is certainly better
than any time scale that could be established there in lieu of landing
a cesium chronometer. To other applications 2 ms in a year may be
intolerably large.

So the question remains: At what level do distributed systems need
access to a time scale which is uniform in their reference frame?
And my question: Can something as naive as POSIX time_t really serve
all such applications, even the ones on earth, for the next 600 years?

Steve Allen                 <>                WGS-84 (GPS)
UCO/Lick Observatory        Natural Sciences II, Room 165    Lat  +36.99858
University of California    Voice: +1 831 459 3046           Lng -122.06014
Santa Cruz, CA 95064     Hgt +250 m
Received on Fri Jan 12 2007 - 11:27:13 PST

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