Hi A lunar setup would only give you data for part of the day. You would relax the flywheel requirement. Net result likely would still be a maser / cesium combo at each site. Not real clear how you would model clouds and weather into the availability equation. Some of the things that 100% take out GPS also kick up a LOT of dust. There is a point where the dust locks up all the turbines and there's nothing to track....
Bob On Sep 10, 2010, at 2:42 PM, jimlux <[email protected]> wrote: > Stanley Reynolds wrote: >> On the crazy side another common view object is the lunar laser ranging >> retroreflector array. Has been improvements in cost of lasers and telescopes >> in the past 41 years and it doesn't appear to be headed for shutdown anytime >> soon. >> > > Hmm.. the SNR isn't all that huge on the echo. The target is say, 1 square > meter, at a distance of 300,000 km. > > The beam divergence coming back is about the same as the outbound (that is, > in order to cover 300km on earth, you need to have a spot on the moon about > 300km in diameter).. So the laser power will be spread out by a factor of > 71E9.. (about 110 dB). The power reflected back, if intercepted by a 1 square > meter aperture will have the same "loss" for a round trip loss of around > 220dB. > > Radiate 10 Watts, and you're seeing -210dBW coming back.. That's going to be > tough to detect. Just how many photons/second is that? And what's the dark > current/shot noise of your detector (a PM tube, presumably) > > The first experiments with the Apollo 11 reflector were done with the 3.1m > antenna at the Lick observatory.. that's a pretty big telescope. The work at > the McDonald observatory used almost as big a telescope, but did provide > ranging to 1 cm, which is 0.03 ns... > > If we make the assumption that a degradation in position accuracy to 10m > requires 1/10,000 the power.. that would imply you could use a telescope with > 1/100th the area, or about 1/10th the diameter.. that's in the reasonable > range..30-45 cm aperture is an off the shelf commodity item. > > http://www.physics.ucsd.edu/~tmurphy/apollo/apollo.html talks about "few > picoseconds"... > > they use a pulsed laser with a few watts average power 115mJ/pulse at 20Hz > with a 3.5 meter telescope making a 1.8 km spot on the moon. For common view > sync, you need to have the spot bigger, as mentioned above, which is nice, > because it means you don't need as big a telescope to collimate the beam. > (interestingly, they use a XL-DC GPS disciplined oscillator as their > reference) > > > In other parts of that site, they say that getting cm scale precision > requires about 10 photons.. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
