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Re: Some P4 moon landing ideas :-)



Remember, though, that the moon librates several degrees either side of 
earth-facing, thanks to an elliptical orbit and its polar moment of 
inertia.  If you have an antenna with a beam tight enough to illuminate 
the earth without much overillumination, you're going to have periods 
about every other week when the beam completely misses the earth.  If 
you make the beam wide enough to cover the earth throughout the 
libration, you're going to lose several dB you can't afford.  The 
tracking mechanism won't have to track far, but it will definitely need 
to track over a few degrees as the earth moves back and forth in the sky.

Only reason this isn't discussed more than it is is that a) the only 
time people were on the moon they weren't there more than a few days at 
a stretch, and b) the last time lunar libration was a major issue for 
most folks was when we were doing intensive photo-mapping of the lunar 
surface from earth to plan landing sites, and libration helped NASA map 
about 55% of the lunar surface by terrestrial photography.

Yes, you need tracking.

On Monday, July 1, 2002, at 05:26 PM, Reicher, James wrote:

> The high gain antenna wouldn't need any steering to look back at Earth, 
> once
> it was set.  The Moon is in a tidal lock with Earth and is ALWAYS 
> showing
> the same side to us.  Aiming a gain antenna to lock in would be 
> relatively
> easy since once the aim is set, you'd never have to move it again!
>
> You could do aim your Earth-based antenna with a sighting scope and 
> merely
> adjust manually over time as the Moon travelled overhead.
>
> -----Original Message-----
> From: Edward R. Cole [mailto:al7eb@ptialaska.net]
> Sent: Monday, July 01, 2002 4:00 PM
> To: amsat-bb@AMSAT.Org
> Subject: RE: [amsat-bb] Some P4 moon landing ideas :-)
>
>
>
>> I'd like to see a concept in which a lunar-based relay would be more
>> advantageous than a satellite.  The Moon is about 8 times further away 
>> than
>> AO-40 at apogee (~18 dB more path loss).
>>
>> Ken Ernandes, N2WWD
>
> Yep!  And the high gain antenna will need precise stearing to stay 
> looking
> at the Earth.  I more probable project might be just a lunar-based
> repeater...for use by the Astronauts to talk back to Lunar Base One from
> their rover!  No particular advantage for Earth-based hams, though!
>
> Ed, AL7EB
>
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