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

Chris Albertson albertson.chris at gmail.com
Fri Apr 4 16:34:55 UTC 2014

On Fri, Apr 4, 2014 at 6:19 AM, Jim Lux <jimlux at earthlink.net> wrote:
> Radio science and navigation measurements are quite impressive in their
> accuracy and attention to detail. measuring range to cm (out of a billion
> km, i.e 1 part in 1E14) and velocity to mm/s is sort of standard.

Looks to be about one order of magnitude better than standard.
They claimed 90 microns/sec velocity in this case.   I was looking for
a document that shows the design of the radio science system in the
spacecraft but did not find it.  Best I can tell is they use a phase
locked receiver transmitter as a kind of transponder so the high
precision clock is on Earth.   They say this is the first time they
are able to detect mechanical movement in the ground station antenna
in the Doppler data.  I guess 90 uM/sec sensitivity just about
everything is a noise source.


Chris Albertson
Redondo Beach, California

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