[Laser] Lunar downlink

[Brent]

Glenn Thomas wrote:

> I gather that there were quite a few projects that attempted to use 
> the Apollo retroreflectors. The one I had in mind was reported in the 
> San Jose Mockery Snooze as using the 150" telescope at Lick 
> Observatory, strangely enough located near San Jose. The details were 
> rather lacking as the article author would have had to explain what a 
> photon is...
>
> I'm not sure that the tale of the observatory location being off by 
> 100m is credible. If the beam is already 2 km on the moon and 18 km on 
> the return, a translational error of 0.1 km seems insignificant. 
> Likewise a return signal measured in single photons seems questionable 
> when you consider the effect of noise due to thermal radiation from 
> the atmosphere and even the telescope itself. Perhaps someone with a 
> better grounding in physical optics than I can comment. Not having 
> worked through the math, I might believe 100's or 1000's of photons!
>
> 73 de Glenn wb6w
>
> At 04:30 PM 2/21/2006, you wrote:
>
>> 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
>
>
>
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>
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---Regarding the the e-mail about the website mentioning "Photons"

Now bare with me here as i just learned this in chemistry class the 
other day, I belive a photon is a part of quantum physics where it is 
described as "Packets" of energy. Looking at the photoelectric effect of 
metal its easy to understand, all the different shades of color in the 
light spectrum contain a different frequency, as such the higher the 
frequency the more "Energy" is in the electromagnetic wave. red is the 
lowest frequency of light, where as purple and violet are the highest, 
if you were to take a metal that is responsive to light, such as in 
solar panels, the electrons in the metal need a certain amount of 
"Energy" to raise out of there bohr model "Level", in essense, leave the 
atom and create an electric potential. Now heres where PHOTONS play a 
part, light is an electromagnetic wave, so in effect is made of energy 
(sorry i cant be any more vague on that, hihi), the energy in the light 
is devised of very very very small packets that hit the electrons, the 
amount of energy in the packets are determined (In this case) by 
frequency. Now when I say very small packets im (Roughly) talking around 
(1 * 10 ^-19),  now the packets "Hit" The electrons and the elctrons now 
have a choice, they can either use all of the energy of none of it and 
CANNOT use more than one at a time, so if the amount of energy isnt 
enough, nothing happens, if it is then it knocks the electrons free. 
when this occurs in solar cells this creates electric current, if you 
shined mostly red light on the cell (Dependent of the metal!) then there 
would be no electric current, but if you shined mostly voilet or other 
high energy light on it thus consisting of higher energy packets then 
and electric current will flow.

    In other instances of quantam physics, the law of "Quanta" which is 
basicaly a term that means energy the things that make "Photons" (Could 
be wrong on that :( ..... looking more simpler ways, the law of quantum 
states that everything can travel or move in increments of quanta, so 
basicly if instead of quanta being somewhere around 1 * 10 ^-19  and was 
really like 10 MPH, If you drove your car down the highway you would 
travel ONLY at 10, 20, 30... MPH and NOTHING inbetween, but since quanta 
is so small its not noticible at all, this reinforces the idea of 
electrons either accepting the WHOLE Photon or nothing at all....

    Now I'm not sure as to what the article was totaly about as I 
haven't read it yet and hopefully we are talking about the same 
"Photons", haha... I felt like wrighting this...so hopefully this helps...