[Laser] moon repeater

[Tim Toast]

i think it would be a worthwhile experiment to take
along a laser repeater with any future moon missions.
Not to mention being inexpensive in the case of the
passive repeater at least. There are many highly
reflective lightweight materials that could be used.

The reflectance of the moon's surface itself is very
low of course, maybe 5% or less? A plain white sheet
for a reflector is better than nothing but is
wastefull because it scatters the light in all
directions.

Better still, those screens that are used for motion
picture projection, which are semi-retroreflective
with a rather broad angle spread. Then next in line
possibly, some kind of retroreflective paint, like the
kind used on street signs and automobile tags. 
That type of material has some significant "gain" in
that it reflects most of the light back to the source,
yet not at so narrow an angle that it would only be
usefull for hearing ones own signals. Somewhere
between the movie screen and a corner cube in
reflectance angle spread. 

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


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Laser digest, Vol 1 #194 - 2 msgs

Message: 2
From: TWOSIG@aol.com
Date: Sat, 13 Dec 2003 00:38:19 EST
To: laser@mailman.qth.net
Subject: [Laser] moon repeater
Reply-To: laser@mailman.qth.net


This seems to be my night for wild ideas.  

I have heard a lot of news media chatter about the
President announcing a bold 
new venture for NASA on the 100th anniversary of the
Wright Brothers flight, 
next week.  What got my interest was returning to the
Moon with a permanently 
manned base.  

If such a base was built and maintained, the chance
for a system like ARISS 
could be added.  Then the system would be accessable
whenever the moon is above 
the horizon instead of a few minutes at a time.  And
gee, why not use a laser?  
Ok, how big?  How to arrange the effort?

To simplify the idea, I limited the concept to a
repeater.  There are passive 
and active repeaters.  The retro-reflectors left on
the Moon by the Apollo 
program are passive repeaters, but are too small and
too narrow.  A passive 
repeater would have to be large and allow a beam to
expand to a large area on the 
return to Earth.  How large would depend on the power
in the transmitted beam. 
 The expansion should be most of the earth to support
EME.  For an active 
repeater, the receiver and transmitter will need
similar field of view. The 
earth stations can use a much narrower transmit FOV.


The Moon looks about the same size as a quarter ten
feet away (a half of a degree).
>From the Moon, the earth looks four times bigger (two
degrees).  If a laser is on 
the Moon, it will be easier to detect when it is in
shadow and the earthbound field 
of view does not include any of the Moon that is
Sunlit. So receiver field of view 
should be less than 
Lots of amateur astronomers view the Moon on a variety
of telescopes.  A lasercomm 
system put up there should not interfere with their
hobby, but should not require 
an exotic optical system at either end.

Would a laser pointer on the Moon apear brighter than
a sunlight reflection from 
shinny object (say a flat sheet of aluminumized mylar
10 feet by 10 feet) to an 
observer on the Earth?  If not, then I am guessing
that it would not interfere 
with most amateur Moon watchers any more than the Moon
Base itself would.

The ideas are disjointed and incomplete.....are they
interesting?


James
N5gui


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