[time-nuts] seeking a time/clock software architecture

Poul-Henning Kamp phk at phk.freebsd.dk
Fri Sep 23 23:01:50 UTC 2011


In message <4E7D0353.2040704 at earthlink.net>, Jim Lux writes:

>But as we move towards constellations of spacecraft with LONG light time 
>to earth, that whole time correlation process needs to be done 
>autonomously.  So the process of converting "local count" to "time in 
>some universally agreed scale" and back has to be done locally.

Doesn't GR sort of make "universally agreed scale" a pretty interesting
concept ?

But more importantly, have you done any estimates of the precision/
required input ratio for this ?

I would seriously look into broadcasting a usable time signal to
the constellation of vehicles, to use as common reference, rather
than have each of them attempt dead reckoning of their own clock
to a paper timescale, which quickly runs into sensor input limitations.

By broadcast I don't mean you have to build an antenna tower, there
are plenty of suitable signals out there already.

Presumably they are going to point an antenna back at earth, adding
a small newtonian telescope with a long-IR sensor next to it, should
give you a signal with a interestingly complex but mostly periodic
waveform, which the vehicles in the constellation can use as
"conductors baton".  Other candidates are Jupiters moons (always
a favourite), pulsars (Probably needs to big antennae?) GRB's &c.

>A pox on "put it in XML"..  As far as I'm concerned that's no better 
>than saying "put it in an ASCII text file". 

Well, it's easier to deal with newlines in strings in XML, but otherwise
I fully agree :-)

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.



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