[time-nuts] Papers on timing for lunar laser ranging
jimlux at earthlink.net
Fri Jul 7 17:59:33 EDT 2017
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 ?
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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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