David C. Partridge wrote:
Jim is it possible you just gave a workable solution: Equip each site with a small radio telescope and watch pulsars.
Aren't pulsars a reliable accurate time source or do they not provide the 30nS over ten days accuracy?
Pulsars *are* pretty stable.. the problem is whether propagation is
stable enough. Maybe with a flywheel..
GIMF (pulsar time stability) and it turns up a paper by Petit on DTIC
(the research was done in 1995 at BIPM in France)
http://www.google.com/url?sa=t&source=web&cd=1&sqi=2&ved=0CBcQFjAA&url=http%3A%2F%2Fwww.dtic.mil%2Fcgi-bin%2FGetTRDoc%3FLocation%3DU2%26doc%3DGetTRDoc.pdf%26AD%3DADA502306&rct=j&q=pulsar%20time%20stability&ei=-DOKTLXwKouqsAO2vNHZBA&usg=AFQjCNEH_epMW_tthuGiX50n93HH4xPxfg&cad=rja
Covers performance and all the perturbations (gravitation effects from
stars alongside the propagation path, propagation through atmosphere, etc.)
take home value: for tau of few years, ADEV of few parts in 1E15.
OTOH this paper also says the measurement uncertainty is 1 microsecond..
Also, one might look at:
tf.nist.gov/general/pdf/2166.pdf
Relativity and Timing in X-ray Pulsar Navigation
This paper is about XNAV (think GPS in deep space, using X-ray pulsars
as the S/Vs)... it seems to show that ModifiedADEV is 1E-13 (an order of
magnitude worse than "atomic clock"; presumbably Cs) at tau of 0.1 year.
ANother chart shows the relative performance of a whole raft of clocks
(and you can see why everyone is excited about JPLs Hg-ion clock...) In
any event PSR 1937+21 is about 1E-12 at tau of 500,000 seconds..
probably not good enough for the OP's need. (PSR 1937+21 has a period of
about 1.5 msec, by the way.. if pulsars are really a spinning star,
that's mighty impressive)
thesis.library.caltech.edu/3590/
describes work on another millisecond pulsar.. the abstract says 100ns
uncertainties, and long term (3yr) residuals of 500 ns.
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