Re: [LEAPSECS] RAS hits the news

From: Ed Davies <ls_at_EDAVIES.NILDRAM.CO.UK>
Date: Mon, 26 Sep 2005 21:34:22 +0100

I wrote:
>>So, dropping leap seconds from UTC would cause these receivers
>>to, eventually, go back 19 years on cold start? Hardly a major
>>catastrophe but worth noting.

Tom Van Baak replied:
> There are no proposals to "drop leap seconds" as
> such. The proposal, as I understand it, is/was to
> hold leap seconds at their current value.

Of course - by "drop leap seconds" I meant drop them
from the specification so that no further leap
seconds would be inserted. The current offset between
UTC and TAI (and therefore GPS time) would be maintained.

>
> In this case no computer or GPS receiver or cell
> phone or clock appliance or any man-made timing
> related intra-planet technology would go forward
> or back or anything. Observe that nothing will break,
> for example, if the 12/31/2005 leap second were to
> not occur.
>
> The only problem is that UTC would soon diverge
> from UT1 beyond 0.9 seconds and so extra-planet
> devices (e.g., precision telescope systems) would
> need correction at some point. This introduces a
> large set of interesting, legitimate, philosophical and
> financial questions by, especially, astronomers.
>
> But either way, nothing with GPS receivers will break.

Not immediately.

But a GPS receiver which uses the current leap second
offset (UTC against GPS time) to help guess which 1024
week period it is in will _eventually_ not work quite
right.

If no more leap seconds are inserted the UTC-GPS offset
will stick at about 13 or 14 seconds or whatever it is
now (or will be after the end of this year) which the
GPS would associate with the current 1024 week cycle. On
a cold start in 2025 it will find that same offset and
assume that it's back in 2005 or there abouts.

Actually, things could start to go off the rails in about
512 weeks (about 9.8 years).

As I said, this is not a big issue at all. In particular
most current GPS receivers will probably be dead by then
anyway, though one of my GPS receivers in current use is
over 12 years old.
Received on Mon Sep 26 2005 - 13:35:48 PDT