[Laser] pictures from the Moon

[laser@mailman.qth.net]

Well, I was glossing over a lot of details.  Yes the Moon wabbles.  How much 
I don't know.  I think it is an East-West wobble.  I came across the 
information in a lunar atlas.  The statement was made that it was possible to produce 
photographic maps of a few percent more than half of the Moon's total surface.  
(The atlas was published before satellites took pictures of the Moon from 
space.)

If the wobble is small compared to the beam width, then there is no problem.  
Well not much.  If the wobble is East-West, it will affect the time that the 
signal can be aquired and when it will be lost.  If the wobble is North-South, 
then it will affect the Northern amd Southern extremes of the spot.  All of 
the effects can be predicted, and matchting the predictions to the actual 
performance would make dandy science projects!  ( I warned you I used to teach Math 
and Science. )

If the wobble is large compared to the beam width, then active compensation 
will need to be applied.  The good news about active compensation is that if we 
lock the laser (or lasers since I expect that 10 to 20 will be needed to 
cover the Earth with some overlap.) to the camera (or cameras  - why not several 
with different spectra and magnification ) then when the camera is centered on 
the Earth, the beams will stay on track.

The issue of active compensation may not depend on wobble.  There is a more 
important effect that may be best solved by actively trimming the direction of 
the laser beams.  The orbit of the Moon is inclined with respect to the 
Earth's equator.  From Earth, that causes the Moon's path through the sky to move 
North and South.  It is most notable in the polar regions where the Moon will 
rise and set instead of riding along the horizon.  From the Moon, the Earth will 
apear to rock back and forth, sometimes showing the North Pole, some times 
the South Pole.  I seem to recall that the orbit is inclined by about 11 
degrees.  If I had one laser that I want to track New York, then I need to adjust it 
for the "rock".

On the other hand, if the East-West wobble is small enough, then a bank of 
lasers with overlaping Latitude coverage would work.  ( I should draw a diagram, 
'cause that explanation is startin' to confuse me. )  

James
N5GUI


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In a message dated 2/22/2004 11:08:27 AM Central Standard Time, 
rob.carr@verizon.net writes:
On Sun, 22 Feb 2004 11:30:24 EST, you wrote:

>The Moon is tide locked 
>to the Earth so that once aligned, neither the camera nor the downlink 
>antennas would need to be adjusted. 

If I remember right, there's some wobble to it. I wonder how the
wobble compares to the spread of the laser beam?

Of course, the trick would be to make the laser beam wide enough that
the variation in the moon's orientation w.r.t. the earth wouldn't
matter.

Also, it just hit me - the moon is tidally locked - the earth isn't.

Danged cold medicine has me dragging.

Rob