[LEAPSECS] Schedule for success
seaman at noao.edu
Sun Dec 21 19:09:57 EST 2008
Poul-Henning Kamp wrote:
> In message <407EB3F6-55BB-4E60-8D20-C909EA92E6B9 at noao.edu>, Rob
> Seaman writes:
>> Consider the iconic issue of timekeeping for trains, one of the
>> primary drivers for our current standard time zone system. Trains
>> clearly need to be synchronized with external clocks. Trains clearly
>> have some mechanism or set of procedures (imperfect or not) for doing
>> so. So they don't match the question asked.
> Modern trains run at speeds of roughly 100 m/s. They care very much
> about seconds and fractions thereof.
> In fact, they run so fast that a special version of the GSM mobile
> standard called "GSM-R", has been created for train-control
> The main difference between plain GSM and GSM-R is that the latter
> allows for dopplershift up to 140 m/s, but now railway people have
> started bitching about that not being enough margin.
> If you want to know what non-antique rail-road control looks like,
> search for and study "ERTMS".
Very informative! (Not a hint of irony. Thanks for the info.)
However, it still doesn't address the question as asked.
James Cloos wrote:
> Anything which uses a remote system to sync its time is good; leap
> second announcements are part of getting a time sync.
> Anything which does not require <=1 sec time-of-day accuracy is also
> good. They simply do not care.
> So what is left?
You may disagree with his premises, but the request was for candidates
for completely standalone systems requiring high precision clocks.
Surely the (very interesting) planes, trains, shipping, power and
military applications you mentioned fail to satisfy the first premise,
whether or not they meet the second premise.
The closest I've come up with is a self-orienting telescope system
I've heard off that can (in theory, at least) be deployed by
parachute. I'm pretty sure it uses GPS, though.
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