[X] My Assistant

[hal_9000]

From http://www.signonsandiego.com/news/science...z1c13laser.html

Laser light aimed at reflectors left on lunar surface could pinpoint distance from Earth - and test Einstein's theory
By Bruce Lieberman
UNION-TRIBUNE STAFF WRITER

July 13, 2006

On July 21, 1969, Neil Armstrong and Buzz Aldrin propped an array of reflectors in the lunar soil – one of several science experiments they deployed a day after becoming the first humans to set foot on the moon.

A month later, a small group of astronomers bounced a pulse of laser light off the reflectors and caught the return signal with a telescope at Lick Observatory near San Jose, in Northern California. By measuring the time it took for the pulse traveling at the speed of light to return, scientists could determine the distance between the Earth and moon.

PDF: http://www.signonsandiego.com/uniontrib/20...mages/quest.pdf

[nprev]

Hmm...I wonder if we could measure the rate of dust deposition (if any) on the reflectors due to the electrostatic effects of the lunar "sunrise glow" using these methods? Useful data on two fronts, if possible (correcting measurement errors for GTR experiments, and of course assessing lunar environmental effects applicable to UM & "M" SF).

[Phil Stooke]

My understanding is that there has been no detectable degradation to the Apollo LRRRs in 35 years due to dust, deposited by any mechanism. Personally, I'm more than a little sceptical of the Lunokhod-2 result on sky brightness. I would want to look carefully at other possible explanations for those observations before concluding that they had to be caused by levitated dust.

Phil

[djellison]

Indeed, how could one tell where the dust came from? It could be micro impact ejecta etc.

Doug

[nprev]

Good point, Doug, and thanks for pointing out that this has been at least somewhat investigated, Phil. Generally, then, this is good news for hardware survival on the surface.

Re the "skyglow": Didn't at least one of the Surveyors make a similar observation?

[edstrick]

The Surveyor observations were made on most missions, looking to the west after sunset, with varying time exposures. There was a beaded glow along the horizon some times, which *I think* was interpreted as sunlight hitting levitated dust just above the surface. There was also fainter, more diffuse glow, that merged with the outer corona and the zodiacal light, and was interpreted as due to sunlight scattered from much higher dust. (I may have some of this scrambled)

The Lunokhod data was from some sort of upwards looking photometer, probably before sunrise and after sunset. It has never been confirmed and as Phil observes, is so limited and un-independently observed as to be suspect.

Future landers should be able to observe the glows with long exposure imaging or sky scanning, preferably at 2 or 3 widely separated wavelengths and a complete set of polarizers.

[nprev]

Thanks, Ed, for the good info.

Hmm yet again...So it still seems possible that lunar dust is fairly mobile in electrostatic terms. I doubt that anyone has done a study of the charging properties of the Apollo reflectors (though I'd imagine based on the lack of observable degradation that they stay pretty neutral and/or the dust vertical transport rate is low indeed), but how about some of the advanced composites that are working their way into aerospace? Seems to me that these materials should be tested for dust-attraction potential BIG time before use on any future lunar missions.

[edstrick]

As I was going to bed last night, I recalled that much of the Lunokhod sky photometer was DAYTIME data. I believe they did have night-time communication sessions, battery powered, but I don't know how many, what time coverage, etc.

Note: Lunokhods had an "RTG-looking" isotope heat-source mounted (as I recall) on the back-rear like the RTG's going to be on MSL. This provided thermal power during the night to keep it from freezing up the way the Surveyors did. It was outside Lunokhods equivalent of the "warm electronics box" and had radiator fins so it could dump heat during the daytime. Note that 3 of 5 landed Surveyors survived lunar night well enough to transmit images and do science on one or more lunar days after landing. (I think the batteries were pretty much shot in all cases).