[fitsbits] Future of UTC

[Arnold Rots]

In the missions I have been involved in, over the past 10 years, we
have consistently used TT in all data products intended for the
science user community.
It's no great hardship, as long as there is someone in the project who
can educate developers on the proper definitions.
The problems we have run into with ground stations and flight
operations teams were caused by a lack of understanding of the
consequences in those circles, poor communication (if any) between
science operations and spacecraft operations, and high personnel
turn-over in the spacecraft operations groups.  This last issue is
probably at the root of it all.
The "good reasons", as I suspect, have to do with legacy software -
the same software that still expresses orbital parameters in things
like Vanguard Units of Length.

  - Arnold

Rob Seaman wrote:
> Clive Page writes:
> 
> > We try to educate all the software developers and users as to the
> > difference between TAI and UTC, and try to get TAI used exclusively
> > in the data analysis chain.
> 
> Sounds like the proper solution - too bad the logic is undermined
> by the next three statements:
> 
> > Unfortunately ground stations invariably use UTC, and
> > have to insert leap seconds manually.
> > The astronomer has little control over this process,
> 
> 1) If ground stations use UTC, perhaps there are good reasons for this?
>    The problem isn't that they use UTC for their own purposes, it's that
>    they don't support alternate time systems for client spacecraft.
> 2) Just because ground stations use UTC doesn't mean that processes
>    can't be used to automatically adjust for leap seconds.
> 3) If astronomers have no control over the current process, why should
>    we assume they will have any more control over whatever process is
>    substituted?
> 
> The problem is not the definition of civil time standards (which
> should continue to rely on UTC approximating GMT).  The problem is
> that professionals in astronomy and elsewhere treat their clocks with
> a lack of care that would be shocking for any other standards of
> measurement.
> 
> If an unsegmented timescale like TAI is what you need - TAI is what you
> should use, and the implications of your project design should be made
> clear to management.  The fix for aging and broken ground stations is
> not to redefine civil time for the entire planet for all time.
> 
> > In summary: my opinion is that many astronomers using space-based
> > observatories will welcome the abandonment of leap seconds.
> 
> To date, only such anecdotal evidence has been offered.  The "surveys"
> have been laughable and the "process" is embarrassing.  It is far from
> obvious that the organizers of the Torino workshop even have standing
> to make such a radical change to the UTC standard.  There appears to
> be great pressure to act quickly - from a shadowy faction with a hidden
> agenda - when we literally have hundreds of years to make up our minds.
> 
> A revision to such a central standard as UTC deserves much more care in
> design and implementation.  All interested parties (literally everyone
> on the planet) should have the opportunity to comment.
> 
> Rob Seaman
> National Optical Astronomy Observatory
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> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head-cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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