[Laser] Lunar downlink - 100m error

[TWOSIG at aol.com]

I think that (once again) I have used too many words to describe what seems  
to me to be a simple situation, and therefore failed to communicate.
 
I think the 100m error in the location of the Lick Observatory telescope  
caused the team to point the telescope in the wrong direction.  
 
The telescope would have been used to observe objects in the sky and would  
have been very precisely calibrated, with reference to the sky.  To  calculate 
the angle to point the telescope at the location of the retroreflector  on 
Moon, the team would have used the latitude and longitude ( now known to  be in 
error by 100m ) to define a point in the sky, in essence drawing a line  from 
the center of the Earth to the telescope.  The telescope would then  have been 
pointed into the sky relative to that.  The angular error caused  by a 100m 
error on the surface of the Earth is about 3.2 arcseconds ( or about  15.7 
micro-radians).  The pointing error would result in an error of about  6,000 meters 
at the Moon, since it is about 60 Earth radii away.
 
This is speculation on my part.  However it seems much more likely  than a 
problem with a pulse gate that was too narrow.  The purpose of the  activity was 
to verify that they could detect the laser pulses, not to refine  the 
distance measurement.  If the problem had been the gate, then they  could have found 
the problem by widening the gate or shifting it a small  amount.  The way the 
story is told, they didn't detect the beam and then  figure out that the 
co-ordinates were wrong.  They corrected the  co-ordinates, then detected the beam.
 
On the number of photons captured - please note that there is a new, larger  
telescope, coupled with a stronger laser pulse than was used by the west Texas 
 program for the last three decades.  This new instrument goes by the  
nickname Apollo, and has only been used for a few months.
 
James
N5GUI