[time-nuts] Water on Enceladus - What does this imply about NASA'a ability to measure frequency?

Alex Pummer alex at pcscons.com
Fri Apr 4 16:58:25 UTC 2014

gravitation measurement, particularly gravitation measurement in space 
is based on the Eotvos -effect see here: 
http://en.wikipedia.org/wiki/E%C3%B6tv%C3%B6s_effect  and here: 
http://en.wikipedia.org/wiki/Lor%C3%A1nd_E%C3%B6tv%C3%B6s    and from 
the begin of the space exploration many space crafts using accelerometer 
based on that Eotvos pendulum, invented by Eotvos in the 
eighteen-hundreds [the richest oilfields in the United States were 
discovered by Eötvös' Pendulum. The Eötvös pendulum was used to prove 
the equivalence of the inertial mass 
<http://en.wikipedia.org/wiki/Inertial_mass> and the gravitational mass 
<http://en.wikipedia.org/wiki/Gravitational_mass> accurately] so no 
speed no time measurement is necessary...
~ a former co-worker of space projects.
A. Pummer

On 4/4/2014 9:01 AM, Jim Lux wrote:
> On 4/4/14 5:01 AM, Dr. David Kirkby wrote:
>> On 4 Apr 2014 08:55, "Tom Knox" <actast at hotmail.com> wrote:
>>>   90 microns  is approx a freq res of about 1 x 3.66 -12
>>> Thomas Knox
>> Since the Doppler shift is prortional to the frequency,  I can't see how
>> one can determine the absolute frequency.
>> But given light travels at 3e8 m/s and they can resolve 9e-5 m/s, I 
>> would
>> have thought that the frequency resolution needed was 9e-5/3e8=3e-13. We
>> are differing by more than a factor of 10.
> It's actually even more tricky, if you think about it, because what 
> you are really doing is making the measurement over some time period, 
> and the path length of signal is continuously varying during that time.
> Not only is Cassini doing it's flyby of Enceladus (and you're looking 
> for small deviations in trajectory from those due to an idealized 
> point source masses), but you've also got your ground stations on 
> Earth moving due to planetary motion, daily rotation, as well as 
> things like solid earth tides moving the DSN station up and down by 
> tens of cm during the measurements.
> Gravity science in deep space is a very time-nutty activity.. it's 
> basically finding all the various sources of change, modeling them, 
> and driving the uncertainties as low as possible.
> They use a collocated radiometer to compensate for the extra delay of 
> the atmosphere of earth.  JPL has all those folks computing earth 
> rotation models, and that figures in (hey, you need to know the 
> rotational velocity of earth pretty accurately, to take that out of 
> the equation).
> The folks who do this spend a lot of time looking at "residuals" plots 
> and trying to make them look like a flat line of zero width.
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