I think there were a couple of steps in between things like time-mation
satellites and such precursors to GPS. But I believe that CS references
were trucked around for a long time.
Regards
Paul
WB8TSL

On Mon, Mar 3, 2014 at 8:17 PM, Jimmy Burrell jimmydburr@gmail.com wrote:

Hi Jim,

Nice video. I had not see that old one before. Someone at NPL must be going through archives. That's very nice of them to post it. Did anyone spot the date of the filming?

My understanding is that the era of traveling clocks gradually ended as various methods of satellite time transfer began. However people still use "traveling clocks" today as a backup for GPS, or to double check GPS, or in places where GPS cannot be received, or when one needs accurate results quickly without waiting for GPS averaging or post-processing. So the practice is not dead. Most recently we all saw it used to validate the neutrino timing experiments.

Traveling clocks can also be used to demonstrate time dilation: http://leapsecond.com/great2005/

For more info on the traveling clock era make sure to read these four HPJ articles:

World-Wide Time Synchronization, 1966
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1966-08.pdf, page 13

A New Performance of the "Flying Clock" Experiment
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1964-07.pdf, page 1

Correlating Time from Europe to Asia with Flying Clocks
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1965-04.pdf, page 1

'Flying Clock' Comparisons Extended to East Europe, Africa and Australia
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1967-12.pdf

/tvb

----- Original Message -----
From: "Jimmy Burrell" jimmydburr@gmail.com
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Monday, March 03, 2014 5:17 PM
Subject: [time-nuts] Time transfer, internationally before GPS

Hi

A traveling clock process is still the only way to fully validate a local time setup. The NIST modems can get close, but a clock (second opinion) is the only way to be sure.

Bob

On Mar 3, 2014, at 9:09 PM, Tom Van Baak tvb@LeapSecond.com wrote:

The piece didn't say anything about correcting for acceleration.

Regards.

Max.  K 4 O DS.

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----- Original Message -----
From: "Jimmy Burrell" jimmydburr@gmail.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Monday, March 03, 2014 7:17 PM
Subject: [time-nuts] Time transfer, internationally before GPS

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Hi

One of the early relativity confirmation experiments was done with very similar clocks before that film clip was made. There were a number of corrections made as part of the trip. One of them was to re-confirm the traveling Cs once it got back to it’s starting point. You only could “use” the trip if the Cs came back home still on time.

There were a lot of satellite time transfer experiments in the 60’s and 70’s. They worked well enough to reduce the frequency of clock trips, but not well enough to eliminate them. The GPS common view stuff was the first approach that (with proper calibration) got them to a better level of time transfer than a clock trip.

Bob

On Mar 3, 2014, at 9:50 PM, Max Robinson max@maxsmusicplace.com wrote:

Hi Max,

True, but at one point the video mentioned microsecond resolution, and at that level, no relativistic corrections for airplane trips are needed.

If you want to get down to nanoseconds, then yes, you will want to apply altitude (gravitational), velocity, and Sagnac corrections.
You can use my rel.exe tool (www.leapsecond.com/tools/) to calculate the two relativistic effects:

C:\tvb> rel 35000ft 500mph 8hr
** Altitude 10668.000 m (35000.000 ft, 6.629 mi) 1.161e-012 blueshift
4181.381949 ps/hour
100.353167 ns/day
** Velocity 223.520 m/s (804.672 km/h, 500.000 mph) -2.779e-013 redshift
-1000.607783 ps/hour
-24.014587 ns/day
** Net effect (GR+SR) 8.835e-013 shift
3180.774165 ps/hour
76.338580 ns/day
** Duration 28800 seconds (8.000 hours, 0.333333 days)
25446.193322 ps total
25.446193 ns total
0.025446 us total

So for an 8 hour flight at 500 mph at 35,000 feet the time dilation correction is only about 25 ns.
Add to that the Sagnac correction for East-West or West-East travel between USNO and NPL, about +/- 22 ns.

/tvb

Hi

Also consider that the “trip” was not very quick. They were a: spend day or three here, go there (day of travel), spend several days someplace else, move on to next location. Eventually you returned the clock to it’s starting point. The “trip” was only good to something related to the drift of the Cs.

If the clock as it bounced around was good to 1 ppt, that’s 86 ns per day. If the trip was 10 days long, there’s a good chunk of a microsecond involved. If you go back into the FCS or PTTI proceedings you can find the data. They spent a lot of time on data reduction after the trip. Desk time was cheap compared to travel time. I don’t think you will find numbers under a few hundred ns claimed for these sort of multi site, many days crossing oceans trips.

Bob

On Mar 3, 2014, at 11:04 PM, Tom Van Baak tvb@LeapSecond.com wrote:

Since the original question was about alternatives to the traveling
clock method before the advent of GPS, I remember two that were used by
NASA to check the synchronization of their Deep Space Network facilities
around the world.

• Moon bounce: A PN code was modulated on a microwave signal that was
  sent from the Mohave desert (there were a suitable transmitter - antenna
  there) to the Moon and its reflection was picked up in the facility to
  be synchronized.. To simplify the receiving equipment the code was
  continually compensated for the varying round trip distance between
  stations and it was correlated with a ramped model in the receiving
  end.  The output was drawn on a strip chart recorder and some
  interpretation was needed to estimate the clock difference.  The
  accuracy was said to be about 1 us but the system was not  very popular
  within the transmitter and the receiver crews.
  -VLBI:  Among other observables, VLBI can be used to get very good
  estimations of the clock difference between stations.

A traveling clock was also used, there were lots of stories of afraid
pasengers traveling close to the "Atomic Clock " and for making the
thing more frightening it was a HP Cesium with the Patek Philipe analog
clock in the front conspicuously ticking.  They were assured that it was
not an "Atomic Bomb" !!!.

Regards,
Ignacio EB4APL

On 04/03/2014 4:23, Bob Camp wrote:

Hi Paul,

I'm glad you know about Timation. At some point every one who plays with GPS should take a quick look back. Here is some light reading. If nothing else, read the Origins of GPS paper (GPS World, u-blox) and the NRL GPS Bibliography.

TIMATION - a GPS Predecessor Program
https://directory.eoportal.org/web/eoportal/satellite-missions/t/timation

First GPS NAVSTAR Satellite Goes on Display
http://www.nrl.navy.mil/media/news-releases/2013/first-gps-navstar-satellite-goes-on-display
http://www.nrl.navy.mil/PressReleases/2013/25-13r_NTS-2_1620x2649.jpg (worth every pixel)

The Origins of GPS, and the Pioneers Who Launched the System
https://www.u-blox.com/images/stories/the_origins_of_gps.pdf
http://gpsworld.com/origins-gps-part-1/
http://gpsworld.com/origins-gps-part-2-fighting-survive/

Initial Results of the NAVSTAR GPS NTS-2
http://tycho.usno.navy.mil/ptti/1977papers/Vol%2009_13.pdf (USNO copy)
http://leapsecond.com/history/1978-PTTI-v9-NTS-2.pdf (high-res from original)
http://leapsecond.com/history/Ashby-Relativity.htm
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA058591
http://www.dtic.mil/dtic/tr/fulltext/u2/a058591.pdf

NRL GPS Bibliography
http://www.nrl.navy.mil/content_images/MR8988.pdf (46.0 MB)
(An Annotated Bibliography of the Origin and Development of the Global Positioning System at the Naval Research Laboratory)
http://www.gpsdeclassified.com/wp-content/uploads/2013/08/NRL_GPS_Bibliography-web.pdf (5.5 MB)

/tvb