[Laser] moon repeater

[laser@mailman.qth.net]

I like the thinking that my weird ideas generated.  I don't know a whole lot, 
but I have two comments on the excerpt I copied below.   

On using the Apollo retro reflectors, please forgive me if my memory is 
faulty, but I think that a web site on the Lunar range experiment at the McDonald 
observatory in west Texas described the experiment.  In it, a high energy 
compressed laser pulse is sent through a one meter diameter telescope at the tar
get.  The light pulse expands from one meter to about two kilometers.  The 
retroreflector panel is about area of a disk a half meter in diameter, and reflects 
almost all of the incident light in a beam that returns to the earth with an 
expansion to an area of about 20 kilometers.  The photons of the beam are 
collected in a 1 meter telescope (I don't remember if it is the same one, or 
another.)  The point of this description was that they collected one photon from 
most of the pulses.  They then ran a statistical analysis on when the photons 
were received to use it it as a distance measuring device, which by now has an 
accuracy of about one or two inches.   Also as I remember there are three Apollo 
retro-reflectors and another one that I think is French made on a Russian 
probe.  They have been tracking not only the orbit of the Moon, but its "rocking" 
as well.   Cool stuff.

For a communication from the Moon to be received on the Earth, the beam will 
need to be more powerful when it leaves the Moon than the above system.  If 
you send a beam from Earth to the retroreflectors, you will need a much narrower 
beam or a lot more power.  If a lower power beam is sent to the Moon, it will 
need to be tightly columated to have a similar energy.  I guess that some 
astronomers (amateur or not) would know what kind of telescope would be needed.   
  On the down side, I think that any beam from the retroreflectors would come 
back to the Earth in a beam 20 kilometers around its origin.  EME for 
neighbors.

 That brings me to the other point about retroreflectors.  If a beam comes 
from the Earth, it does not matter how much the Moon rocks from side to side.  
The return beam will be back toward the line of origin with some additional 
expansion.  A retroreflector will need no more than two degrees of expansion.  
Practically, I think that one degree will be plenty.  The typical STOP sign is a 
lot more beam expansion.

Someone else suggested that the natural reflectivity of the moon is about 5%. 
 I think the number is more like 2 - 3 %.

As much as I like the I like the idea of a passive reflector, I am afraid 
that it will need to be too big for the first decade of a lunar base.  



James
N5GUI




I think most kinds of retro-reflective paint have a
backscatter spread of about 5 to 10 degrees? That
might be great for covering the whole earth as seen
from the moon (2 degrees) without wasting an excessive
amount of the energy. 
Even though the moon keeps one side always toward the
earth, it liberates a bit during the month by a few
degrees (6 or 7). So an extra margin on top of that 2
degree "earth width" would take that into
consideration as well. Also with the added benefit of
being much less critical in alignment when being set
up, compared to say, a plane mirror type reflector. 

I was wondering if anyone has tried using the Apollo
retroreflectors with low power lasers in combination
with the 20 hz QRSS type modulation? Since that seems
to be the cutting edge of weak signal tech these days.
Even though it would only be usefull for hearing your
own signals i suppose.

Tim
toasty256@yahoo.com