In message <4e7cdeb0.8070...@earthlink.net>, Jim Lux writes: >Actually, the really annoying one is where I have a good clock that's >stable, but I need to keep adjusting "time" to match someone else's >terrible clock. Most clock disciplining/time propagation models assume >your bad clock is following a better clock.
That is exactly what happens when you put an OCXO or Rb in a computer and run NTPD against a server across the internet :-) I still have a hard time drawing a boundary about this next level up, and maybe I'm misunderstanding you, so let me think out loud for a moment: Its pretty obvious that you can build a suitably general mathematical model that will cover anything you can expect to encounter: A polynomium of a dozen degrees will catch any PLL-like regulation pretty well, add a fourier series for periodic terms like your temperature variations and finally chop it into segments to correctly deal with discontinuities from power failuers or upsets. But isn't that so general that it becomes meaningless ? Determining two or three dozen Finagle constants doesn't sound like anything close to "real-time" to me, and it all hinges crucially on the mathematical model being expressive enough. Something like the SOHO unthaw would be a really tough challenge to model I think. The opposite approach is accept that clock-modelling is not the standardized operation, but representing the data to feed into the clock-modelling software should be a standard format, to facilitet model reuse. Some of that data is pretty obvious: Time series of clock offset estimates: When Which other clock Uncertainty of other clock Measured Offset Uncertainty of Measured Offset Craft orbital params XYZT, model gets to figure out what is nearby ? or Parametric model (in orbit about, ascending node...) And then it gets nasty: Vehicle Thermal balance model a function of: Vehicle configuation Vehicle orientation Nearby objects (sun, planets, moon) Wavelength Clock model: a function of: vehicle temperature, bus voltage gravity magnetic fields from craft vibration (micrometeorites, think: Hipparcos) clock age random clock internal events And the list probably goes on and on, until we come to individual component failure effects. Missing in this picture is the organizational boundaries: The mission data comes from one place, and the clock model or clock parameters are probably delivered by the manufacturer of the specific device? How many of these parameters you need to include will of course depend on the exact vehicle and mission requirements. There is a heck of a difference between a commercial geo-stationary comms satelite and Gravity Probe B and Gaia. One can always say "put it in XML and hope for the best" but that's not much of a standard, is it ? -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@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. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.