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

[Chris Albertson]

I just read about a discovery of a liquid water ocean on Saturn's moon
Enceladus.  The method used was to measure the velocity of a
spacecraft as it makes a close fly-by.  Gravitational anomalies will
cause the spacecraft to speed up or slow down as it flies over massive
objects like mountains.  With three pass they now have a 3 dimensional
map of density distribution.  It must be very sensitive if they can
tell liquid water from ice by its gravitational field. (or even rock
from ice)

They say they can measure the spacecraft's velocity to 90 microns per
second.   They do this by measuring the Doppler sift of the
transmitter.    I've been trying to figure out what 90 microns/sec
means in terms of frequency.   But I think(?) I need to know the
orbital velocity of Enceladus.
-- 

Chris Albertson
Redondo Beach, California