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

Jim Lux jimlux at earthlink.net
Fri Apr 4 13:50:28 UTC 2014

On 4/4/14 4:30 AM, Bob Camp wrote:
> Hi
> Back when they were designing this stuff, they were very interested in getting into the parts in 10 to the 15th. They didn’t get there, but that was the desire.

Roughly that...
http://lasp.colorado.edu/~horanyi/graduate_seminar/RSS.pdf is a good 
presentation with design and performance at a high level. It has plots 
of the USO and maser performance, etc.

http://lasp.colorado.edu/~horanyi/graduate_seminar/Radio.pdf is a good 
paper describing Cassini Radio Science looking for Gravity waves. The Ka 
band system has some issues in flight.


gives some numbers.. see page 19

the DSN antenna is on the order of 1E-15 at tau=1000 seconds if you're 
careful, 1E-14 under normal operation

Tropospheric scintillation is also a factor..

I doubt we will ever see a telecom subsystem as complex and 
sophisticated as Cassini's ever again.  The modern trend is to less 
redundancy, and higher level of integration in the boxes so fewer total 

For the Juno mission on it's way to Jupiter, we were looking for the 
radio's contribution to the measurement uncertainty being around 4E-16 
at 1000 seconds.
https://www.youtube.com/watch?v=ulzq_mlU-fA is a high level explanation 
of the gravity science

When the Deep Space Atomic Clock (a trapped Hg ion) flies, that will 
change a lot of radio science, because we will be able to make more 
accurate one-way measurements.  They are hoping for an overall 
improvement of 2 orders of magnitude.

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