[time-nuts] would an optical primary standard provide any general benefit?

[Jim Lux]

On 4/3/12 12:49 AM, Azelio Boriani wrote:
> Yes, but nonetheless why not develop more stable primary clock sources? We
> can always take care of the dissemination in the meantime and try to
> develop a more precise time transfer method.
>
> On Tue, Apr 3, 2012 at 2:39 AM, beale<beale at bealecorner.com>  wrote:
>
>> Having read this NIST review paper by Thomas E. Parker, "The uncertainty
>> in the realization and dissemination
>> of the SI second from a systems point of view"
>> http://tf.boulder.nist.gov/general/pdf/2564.pdf
>>
>> ...it seems that any potential improvement in frequency standards (Cs
>> fountain ->  optical clocks) will not benefit most time/frequency users,
>> because existing long-range time-transfer methods (TWSTFT and GPS carrier
>> phase) are still limited to at best 2E-16 for 30-day averaging, and there
>> is no generally practical way to improve them currently in sight.  (Laser
>> ranging of satellites being considered not generally practical). Just
>> curious what people think, is this too pessimistic a view, or is it fair to
>> say that having a 10x improved primary standard would not improve stability
>> or accuracy for anyone outside of stabilized optical-fiber distance from
>> such a standard?
>>
>>


In general, as a technology developer, I agree with you, but the sources 
of money with which to develop technology often have a slightly 
different view.

If one has limited resources, there's a desire to spend the resources 
where they will produce something that is usable.  Since there are more 
things to spend money on than there is money to spend, the money has to 
get allocated, and that allocation process cannot be done in a truly 
objective way.

In my own field of space telecommunications, it seems self evident to me 
that faster data links are better, but from the perspective of a 
national funding source, they have to decide where to spend their money: 
faster telecom; new science instruments; precision pinpoint landing, 
etc.   So what they do is look for places to spend money that are 
"enabling" new science.

there is a sort of circular argument.. you need scientists to stand up 
and say "I need communication technology Y to do my science" (creating 
what is known as a "validated requirement"), but, on the other hand, the 
scientists have a very strong incentive to say "I can do my science with 
existing communication technology X", because that makes their mission 
proposal lower risk (or, at least, reduces  the risk in "infrastructure" 
sorts of ways.  That is, they'd rather spend their risk budget on the 
science measurement, not on getting the data back to Earth.


So, the comment from Parker is quite relevant.  If you have no way to 
distribute your incredibly precise time, there's no way to get it to 
users, so it's not clear whether you should spend your money getting the 
precise time, or spend your money on trying to figure out a way to 
distribute it, first.  Or, should you make your really accurate clock 
small and portable, so you can effective distribute it by making lots of 
them (they are *primary* standards, after all)

This is why there is interest in a 1kg, 1 liter Hg+ ion clock for 
spacecraft, of course.  And you too can have a demonstration of one in 
space for around $100M.

http://www.nasa.gov/mission_pages/tdm/clock/clock_overview.html