[Secretariat] [CESG] IERS Questionnaire to survey opinion concerning a redefinition of UTC

Hooke, Adrian J (9000) adrian.j.hooke at jpl.nasa.gov
Thu Jul 21 11:16:14 EDT 2011

I agree completely with Peter. The proposal has always seemed to be flawed in that they want to change the basic meaning and definition of UTC itself: at one point in time it would be leap-second based and a picosecond later it would not. That seems likely to cause huge and unknown headaches for the far-flung embedded code-base that would have to be simultaneously updated at that precise picosecond. Why not simply define a new time code?

I think that CCSDS does need to take a firm stand on this. As Peter points out, the current proposal seems to have been formulated by narrow interests.


From: Shames, Peter M (313B)
Sent: Thursday, July 21, 2011 11:09 AM
To: Hooke, Adrian J (9000); Gian Paolo Calzolari; CCSDS Engineering Steering Group - CESG Exec
Subject: Re: [Secretariat] [CESG] IERS Questionnaire to survey opinion concerning a redefinition of UTC

We had a lengthy set of discussions on this topic a while back.  It was the uniform opinion of the ground communication system people that things are handled now without a problem and that they could readily make the changes if this new approach were adopted.

On the other hand, there was also some strongly expressed concern among various science and mission operations people that this was a bad idea and would cause them lots of grief down the road.  As Adrian points out, this seems to be driven by the "clock" and GPS guys who seem to have a rather different opinion than the mission operations and science types.

It is rather instructive, I think, that one possible solution to changing the definition of UTC is to cause the creation of some new means of publishing DUT1.  Isn't that just doing that same thing that is done now, accomplishing the same thing in the end, but by different means?   I rather wonder why they didn't just define some new, unconstrained, monotonically increasing, time constant instead of fiddling with UTC?

If MOIMS can take the lead to sort out a CCSDS position within the science and mission ops communities that would be great.

Cheers, Peter

From: Adrian Hooke <Adrian.J.Hooke at jpl.nasa.gov<mailto:Adrian.J.Hooke at jpl.nasa.gov>>
Date: Wed, 20 Jul 2011 10:25:59 -0700
To: Gian Paolo Calzolari <Gian.Paolo.Calzolari at esa.int<mailto:Gian.Paolo.Calzolari at esa.int>>, CCSDS Engineering Steering Group - CESG Exec <cesg at mailman.ccsds.org<mailto:cesg at mailman.ccsds.org>>
Subject: RE: [Secretariat] [CESG] IERS Questionnaire to survey opinion concerning a redefinition of UTC

Gippo: I believe that the official NASA position was to approve this change. On  the other hand I believe that the US Naval Observatory took a contrary position.

However, from a personal engineering (CESG) viewpoint I am not sure that the end-end system rationale for the change is sound . One argument that I heard was that if a launch vehicle wanted to blast off at midnight UTC on New Year's Eve then it would have to hold its launch while the current UTC updated for the leap second. It seems to be an unlikely scenario.

Although the Time Code Format standard may be impacted, the bigger impact may be in MOIMS. There may be literally thousands of pieces of application software embedded across the mission operations community that will have to be changed if the definition of leap-second-based UTC is changed. I am not aware that the mission operations aspects have been analyzed in any detail, though (see attached). The current proposal to change UTC seems to have been formulated mainly by the frequency and timing community, who probably don't know much about space mission operations

I think that MOIMS would serve the community well by studying the mission operations impacts and submitting a formal CCSDS position. Nestor, Roger - comments?


From: secretariat-bounces at mailman.ccsds.org<mailto:secretariat-bounces at mailman.ccsds.org> [mailto:secretariat-bounces at mailman.ccsds.org] On Behalf Of Gian.Paolo.Calzolari at esa.int<mailto:Gian.Paolo.Calzolari at esa.int>
Sent: Wednesday, July 20, 2011 10:21 AM
Subject: [Secretariat] [CESG] IERS Questionnaire to survey opinion concerning a redefinition of UTC

Dear All,
        I wonder whether you are aware of this ongoing activity and of any ongoing position/evaluation within your space agency.

I think that any change for UTC would affect (at least) CCSDS 301.0-B-4 "TIME CODE FORMATS" where it is stated that the "UTC based codes" (i.e. CDS, CCS, ASCII) do require the leap second correction.

Best regards

Gian Paolo


IERS Message No. 192                                       July 12, 2011

Questionnaire to survey opinion concerning a redefinition of UTC

After years of discussions, a proposal to fundamentally redefine UTC
will come to a conclusive vote in January 2012 at the ITU-R in Geneva.
This proposal would halt the intercalary adjustments known as leap
seconds that maintain UTC as a form of Universal Time.

If the proposal is approved, UTC would not keep pace with Earth rotation
and the value of DUT1 would become unconstrained. Therefore UTC would no
longer be directly useful for various technical applications which rely
on it being less than 1 second from UT1. Such applications would require
a separate access to UT1, such as through the publication of DUT1 by
other means.

The objective of the survey is to find out the strength of opinion for
maintaining or changing the present system.

Link to the questionnaire:


Your response is appreciated before 31 August 2011.

Daniel Gambis
Earth Orientation Center of the IERS

IERS Messages are edited and distributed by the IERS Central Bureau.
To submit texts for distribution and to subscribe or unsubscribe,
please write to <central_bureau at iers.org<mailto:central_bureau at iers.org>>.
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