[Laser] Lunar downlink

[TWOSIG at aol.com]

In a message dated 2/20/2006 11:23:37 PM Central Standard Time,  
glennt at charter.net writes:

Uhhh...  as I recall, the official bounce project used a laser of at 
least a few  watts and on the receiving end, a Newtonian telescope 
with a one hundred  fifty (150) inch (!!!) mirror. It took several trys...

73 de Glenn  wb6w






I do not remember the number of joules per pulse used by the laser lunar  
range experiment, or how that translates to watts in the very short pulse.   The 
mirror used at the obseratory in west Texas (my native state) started at one  
meter ( about 40 inches ) and later used a half meter.  As I recall the  pulse 
expanded to about two kilometers at the Moon on a target less than a half  
square meter area and reflected back to a beam about 18 kilometes diameter, into 
 the same telescope.  Most of the return pulses counted as single photons,  
but there were plenty of repeated pulses to get a statistical measurement of 
the  flight time that translates to less than two inch error.  Several  
reflectors there.  I beleive the experiment is still going.
 
I think you may be thinking of the story that the first attempt, to  find the 
reflector left by Apollo XI was agravatingly un-successful.  That  is, until 
someone realized that they had been using the latitude and longitude  of the 
observatory office which was some 100 meters from the telescope.   When that 
correction was made to the calculations for pointing the telescope,  the next 
pulse was detected.  I do not remember which observatory or  telescope was being 
used, but it did seem that bigger than one meter.  It  may have used a 
brighter laser than the Texas instrument.
 
James
N5GUI