[time-nuts] Papers on timing for lunar laser ranging
paulswedb at gmail.com
Fri Jul 7 18:32:51 EDT 2017
Good reads and not even behind a paywall. Pretty neat details and thank
heavens a raspberrypie is in the mix...
On Fri, Jul 7, 2017 at 5:59 PM, jimlux <jimlux at 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
>> 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 ?
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> 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.
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