Discussion:
Project GREAT - Galloping Galileo version
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Mark Sims
2018-12-07 17:38:45 UTC
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Looks like somebody (sort of) duplicated Tom's experiment (and stole the name):

https://www.theregister.co.uk/2018/12/07/galileos_magnifico_measurement_1976_redshift_test_updated/
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jimlux
2018-12-07 20:11:41 UTC
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Post by Mark Sims
https://www.theregister.co.uk/2018/12/07/galileos_magnifico_measurement_1976_redshift_test_updated/
And there's a mention of Tom's experiment in the comments..

So Time-nuts are truly pervasive and omnipresent - just like time.


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Peter Monta
2018-12-08 18:12:16 UTC
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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.

Cheers,
Peter
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jimlux
2018-12-08 18:49:14 UTC
Permalink
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
http://www.leapsecond.com/pages/csac/

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
Sun?



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Poul-Henning Kamp
2018-12-08 18:58:48 UTC
Permalink
--------
Post by jimlux
There are folks developing and flying a Deep Space Atomic Clock (DSAC),
[..]
It will be in LEO, but maybe you can see the variation from the Moon and Sun?
In LEO for testing ? Otherwise the name seems a bit grandiose ?
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
***@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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jimlux
2018-12-08 19:22:44 UTC
Permalink
Post by Poul-Henning Kamp
--------
Post by jimlux
There are folks developing and flying a Deep Space Atomic Clock (DSAC),
[..]
It will be in LEO, but maybe you can see the variation from the Moon and Sun?
In LEO for testing ? Otherwise the name seems a bit grandiose ?
You take the ride you get, I suspect. I've not talked with the DSAC
folks in a while. It might have been a SLS EM-1 originally (to the
moon), but they decided to go with FH, just so they could get a ride. I
seem to recall way back when that they were going to do a "hosted
payload" on something like Iridium Next or a telecom. But that might
also have changed.

Rummaging on the web a bit, I find that DSAC is riding on Orbital Test
Bed from General Atomic

maybe it will be in a higher than usual LEO (I saw mention of 720km) or
elliptical?




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Bob kb8tq
2018-12-08 19:30:31 UTC
Permalink
Hi

You might be surprised by how well the CSAC does in orbit. There have been a lot of cases
over the years where a device has done much better once it is away from “poking fingers”
like pressure and other semi-random stuff ….

Bob
Post by jimlux
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
http://www.leapsecond.com/pages/csac/
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 Sun?
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jimlux
2018-12-08 23:35:11 UTC
Permalink
Post by Bob kb8tq
Hi
You might be surprised by how well the CSAC does in orbit. There have been a lot of cases
over the years where a device has done much better once it is away from “poking fingers”
like pressure and other semi-random stuff ….
Bob
Oh, I'm pretty sure it will do well in a very benign environment - I
joked with the reps that if we could figure out how to vent the
enclosure after on orbit, the whole "getter filling up" issue would go away.

I don't know that I'll be able to measure the performance. We sort of
added it at the last minute, to be able to demonstrate the ability
measure & calibrate an OCXO without a GPS 1pps, and didn't give a huge
amount of thought to how to do real performance measurement.



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