Post by Peter Monta
If a little eccentricity makes for a good test of relativity, wouldn't a
lot of eccentricity be even better? :-)
Does anyone know what clock facilities are on the Parker solar probe?
Atomic clock? And a drag-free mode would have been great too, but I doubt
that was included.
Extremely unlikely.. I know one of the PIs for Parker, I'll ask him.
If anything, they would fly a USO (a really good crystal in a
temperature stabilized enclosure).
I'm flying an atomic clock (a CSAC), launching next week, but it will be
in a circular orbit, and I'll bet the gravity variations are small
enough that they are less than the uncertainty.
The other problem is that you need to *measure* that atomic clock
against something. The best I can do with my CSAC is compare its 1pps
against a Novatel OEM-6 single frequency GPS 1pps, and an onboard 100
MHz oscillator - none of them are outstanding by timenuts standards.
(CSAC is around 1E-12 at 1000-10000 seconds - see
It's about an order of magnitude worse than a PRS-10 Rb)
Tom, with his herd of clocks, can leave some at home and take some with
him, and compare them upon return.
I would imagine that someone looks at the behavior of the atomic clocks
on the GPS satellites in excruciating detail. The signals from GPS are
incredibly well studied, and have been recorded at carefully maintained
ground sites for decades with high quality reference clocks.
There are folks developing and flying a Deep Space Atomic Clock (DSAC),
a trapped Hg-ion, which is substantially better. Launch is currently
March 2019 (on the Falcon Heavy) It's a bit of a beast: 17.5kg, 17.4
liters (a bit bigger than their original goal of 1kg, 1 liter, <grin>)
and 44 watts.
It's supposedly going to be in the 1E-14 range at 1000 seconds, and
1E-15 at 100,000 seconds.
It will be in LEO, but maybe you can see the variation from the Moon and
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