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Re: Repeater on the Moon

Bruce Bostwick <lihan161051@earthlink.net> wrote:

>>3) Pointing the gain antennas.
>This might be an easy one.  How accurately does the antenna need to be 
>pointed?  The earth doesn't move much in the lunar sky, mainly from 
>eccentricity/libration effects, and all of these motions are predictable at 
>least to some extent.  It's probably worthwhile putting in some az/el 
>control of the high-gain antenna into the command system, if nothing else 
>but fine tuning, but your high-gain antenna is going to be pointed pretty 
>close to the earth at all times.  Depending on what the pattern of the 
>antenna is, it might be sufficient to position it so the center of its 
>pattern is aimed at the center of the earth's relative motion -- this would 
>reduce the power demand from steering the high-gain to track the earth and 
>would keep the gain antenna more or less correctly pointed if (i.e. when) 
>the az/el motors fail.

G3RUH wrote an article about this. You can also work it
out from any standard astronomical reference. I find Meeus
to be a good reference.

This is also an utterly fundamental requirement for such
a proposal, since it limits the antenna gain you can use
on the Moon, which determines the RF output power you
must generate to establish communication.

Laura Halliday VE7LDH     "Que les nuages soient notre
Grid: CN89lg                    pied a terre..."
ICBM: 49 16.57 N 123 0.24 W        - Hospital/Shafte

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