[Laser] pictures from the Moon

[laser@mailman.qth.net]

The headlines about returning to the Moon (and maybe a manned mission to 
Mars) seem to be slowing.  Here's an idea that might stir some public interest in 
going to the Moon and developement of laser communication receivers.

If a camera is set on the Moon and pointed at the Earth, the pictures could 
be sent down to on a laser beam.  The pictures would run from interesting ( 
showing the current phase of the Earth and changing weather patterns, even the 
rotation of the globe ) to spectacular ( the Moon's shaddow on the Earth or the 
Earth moving across the Sun during a Lunar eclipse ). The Moon is tide locked 
to the Earth so that once aligned, neither the camera nor the downlink 
antennas would need to be adjusted.   A package of experiments could send data down 
with the pictures.

OK, so that's not such an original idea.  But think of it this way.  If the 
laser downlink transmitter had a 2 milliradian beam width.  At a distance of 
239,000 miles, the spot would be 478 miles across, and the Earth would be 
turning under it.  If I set it to New York City, the spot will cover North into 
Maine and South beyond Washington, DC.  If the beam can be received with a 
telescope of 6 inches, anyone under that spot who can see the Moon, can receive the 
pictures and data with the right equipment.  ( Someone else juggle the numbers 
about how much power is needed for x amount of beam width and y amount of 
aperture on the telescopes.)

Since the Earth is turning under the spot, in about an hour it will shift to 
Chicago.  In another hour, to Denver.  Later Salt Lake City, then San 
Francisco.  Still later it will move across the pacific to Tokyo, Beijing, Ankara, 
Athens, Naples, Madrid and Lisbon.  About twenty-five hours later back to New 
York.  Maybe experimenter in each of those cities could work together.

Take look at a world map and you can see that very different countries share 
Latitude.  By using multiple lasers aligned to differing Latitudes, on camera 
/ experiment site could service all interested sites.   Makes for some 
interesting choices.  If New York wanted a stronger signal so that it could be 
received by smaller telescopes, they could narrow the beam, which they could share 
with Beijing and Madrid, but not Boston or Tokyo.  Of course that might also 
shorten the viewing time.  London could choose a wide beam that  could be viewed 
almost from Moon rise until setting.  The telescope needed to collect the 
data would need to be larger, but the spot would cover all cities from the North 
Pole to southern England.

Another idea:  If the laser beam comming down used multiple encoding, what 
you get from the system will depend on the instrument you use.  A small 
telescope might look a the Moon and not see the beam at all.  A slightly larger unit 
might see the light from the beam and be able to read Morse code identification 
and a coded status or data "word".  A still bigger telescope, might get the 
Morse as an electronically detected MCW tone set.  Still bigger telescope might 
detect that each pulse of the MCW tone is actually PWM with the picture data. 
 

Now for the serious Astronomer, the light from the Moon makes serious sky 
viewing difficult, so I do not see why they would object to a little more light 
from the downlink lasers.  And if they are looking at the Moon, I think the 
changing sun glint from a permanent manned base would be more trouble than known 
laser links at a known schedule.

James
N5GUI


--- StripMime Report -- processed MIME parts ---
multipart/alternative
  text/plain (text body -- kept)
  text/html
The reason this message is shown is because the post was in HTML
or had an attachment.  Attachments are not allowed.  To learn how
to post in Plain-Text go to: http://www.expita.com/nomime.html  ---