Papers on timing for lunar laser ranging
Three recent papers from the APOLLO project showed up on my VoxCharta
summary of arxiv.org which may be of interest to the time-nuts
community. They are to do with improving the precision and absolute
calibration of the lunar laser ranging project based at the 3.5m WIYN
telescope at Apache Point.
The links are:
http://arxiv.org/abs/1707.00204v1 (Timing calibration of the APOLLO experiment)
http://arxiv.org/abs/1706.09550v1 (An absolute calibration system for
millimeter-accuracy APOLLO measurements)
http://arxiv.org/abs/1706.09421v1 (APOLLO clock performance and normal
point corrections)
I was surprised by a few things: 1) that the size of GR effects on the
Moon's position was at the 10 meter level (or ~0.01%
measurable/testable level for the millimeter-level precision reached
by APOLLO) and 2) the relatively coarse frequency steps the XL-DC
GPSDO previously used was capable of. Does anyone know what sort of
oscillator these used ? I thought most (good) OCXOs had/have a EFC at
the 1e-13 level but maybe "back in the day" the availability of
suitable DACs with a large dynamic range was more of an issue ?
Cheers,
Tim
Hi
On Jul 7, 2017, at 4:51 PM, Tim Lister listertim@gmail.com wrote:
Three recent papers from the APOLLO project showed up on my VoxCharta
summary of arxiv.org which may be of interest to the time-nuts
community. They are to do with improving the precision and absolute
calibration of the lunar laser ranging project based at the 3.5m WIYN
telescope at Apache Point.
The links are:
http://arxiv.org/abs/1707.00204v1 (Timing calibration of the APOLLO experiment)
http://arxiv.org/abs/1706.09550v1 (An absolute calibration system for
millimeter-accuracy APOLLO measurements)
http://arxiv.org/abs/1706.09421v1 (APOLLO clock performance and normal
point corrections)
I was surprised by a few things: 1) that the size of GR effects on the
Moon's position was at the 10 meter level (or ~0.01%
measurable/testable level for the millimeter-level precision reached
by APOLLO) and 2) the relatively coarse frequency steps the XL-DC
GPSDO previously used was capable of. Does anyone know what sort of
oscillator these used ? I thought most (good) OCXOs had/have a EFC at
the 1e-13 level but maybe "back in the day" the availability of
suitable DACs with a large dynamic range was more of an issue ?
Consider that in 1974, I could buy a nice new car for less than what a decent packaged
16 bit DAC cost. Go back into the 1960’s and you are up into the “several new cars”
range. Even for NASA projects cost did make it into the equation ….
A 1 ppm EFC and 16 bits gets you to 1.5x10^-11 if everything is perfect. In the typical
case you get to about 6x10^-11. Either way, that’s a long way from parts in 10^-13. It’s also
not the only driver for GPSDO’s doing parts in 10^-11 sort of performance out into the
hundreds of seconds range.
Bob
Cheers,
Tim
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On 7/7/17 1:51 PM, Tim Lister wrote:
Three recent papers from the APOLLO project showed up on my VoxCharta
summary of arxiv.org which may be of interest to the time-nuts
community. They are to do with improving the precision and absolute
calibration of the lunar laser ranging project based at the 3.5m WIYN
telescope at Apache Point.
The links are:
http://arxiv.org/abs/1707.00204v1 (Timing calibration of the APOLLO experiment)
http://arxiv.org/abs/1706.09550v1 (An absolute calibration system for
millimeter-accuracy APOLLO measurements)
http://arxiv.org/abs/1706.09421v1 (APOLLO clock performance and normal
point corrections)
I was surprised by a few things: 1) that the size of GR effects on the
Moon's position was at the 10 meter level (or ~0.01%
measurable/testable level for the millimeter-level precision reached
by APOLLO) and 2) the relatively coarse frequency steps the XL-DC
GPSDO previously used was capable of. Does anyone know what sort of
oscillator these used ? I thought most (good) OCXOs had/have a EFC at
the 1e-13 level but maybe "back in the day" the availability of
suitable DACs with a large dynamic range was more of an issue ?
Cheers,
Tim
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
The XL-DC had a wide array of options. I used to buy them with a low
phase noise 10 MHz OCXO, but there were other options. One of the papers
mentioned 50MHz coming from the XL-DC, so that must have been from a
different flavor of the unit.
Thanks Tim
Good reads and not even behind a paywall. Pretty neat details and thank
heavens a raspberrypie is in the mix...
Regards
Paul
WB8TSL
On Fri, Jul 7, 2017 at 5:59 PM, jimlux jimlux@earthlink.net wrote:
On 7/7/17 1:51 PM, Tim Lister wrote:
Three recent papers from the APOLLO project showed up on my VoxCharta
summary of arxiv.org which may be of interest to the time-nuts
community. They are to do with improving the precision and absolute
calibration of the lunar laser ranging project based at the 3.5m WIYN
telescope at Apache Point.
The links are:
http://arxiv.org/abs/1707.00204v1 (Timing calibration of the APOLLO
experiment)
http://arxiv.org/abs/1706.09550v1 (An absolute calibration system for
millimeter-accuracy APOLLO measurements)
http://arxiv.org/abs/1706.09421v1 (APOLLO clock performance and normal
point corrections)
I was surprised by a few things: 1) that the size of GR effects on the
Moon's position was at the 10 meter level (or ~0.01%
measurable/testable level for the millimeter-level precision reached
by APOLLO) and 2) the relatively coarse frequency steps the XL-DC
GPSDO previously used was capable of. Does anyone know what sort of
oscillator these used ? I thought most (good) OCXOs had/have a EFC at
the 1e-13 level but maybe "back in the day" the availability of
suitable DACs with a large dynamic range was more of an issue ?
Cheers,
Tim
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/m
ailman/listinfo/time-nuts
and follow the instructions there.
The XL-DC had a wide array of options. I used to buy them with a low phase
noise 10 MHz OCXO, but there were other options. One of the papers
mentioned 50MHz coming from the XL-DC, so that must have been from a
different flavor of the unit.
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/m
ailman/listinfo/time-nuts
and follow the instructions there.