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
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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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