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Re: Moon keps



Interesting...  I assume "true" or "ordinary" satellites actually refers to
"artificial" satellites.  In a sense, the Moon is Earth's only "true"
satellite.  All others (that we know of, anyway) are man-made...

(Just having some fun with words here)

73,
Frank
wb2bxo@amsat.org

----- Original Message -----
From: Robert Winingham <kc5ejk@earthlink.net>
To: <amsat-bb@AMSAT.Org>
Sent: Friday, July 06, 2001 4:29 PM
Subject: Re: [amsat-bb] Moon keps


> this question comes up often
>
> type a google search for Moon keps
> like this
> http://www.google.com/
>
> and see
>
> http://www.physics.usyd.edu.au/~ptitze/amsatvk/moonsunfaq.html
>
> short summary
>
> The moon:
>
>       Giving Keplerian elements for the moon is much more difficult. The
main problem is that the moon's orbital plane has a fixed
>       inclination with reference to the ecliptic plane. The moon's orbital
plane wobbles around there and turns once every 18.6
>       years. Seen from the earth, that gives an changing inclination of
about 18 to 28 degrees. The inclination of true earth satellites,
>       on the other hand, remains fixed and the tracking program assumes
that the inclination is not changing. The only way to
>       overcome that problem is to give sets of "Keplerian elements" every
50 to 100 days. In that period the change of the
>       inclination is not too big and the error stays small.
>
>       A second problem with "Keplerian elements" for the moon is that the
moon's orbit is severely perturbed in a way a ordinary
>       satellite tracking program cannot handle. Those perturbations come
from the sun, the earth (not being a exact sphere) and
>       from major planets. To compute those perturbations exactly, we would
need several hundred corrective terms. For the
>       accuracy needed here (1-3 degrees for the usual amateur satellite
antenna), it has been sufficient to correct only for the
>       varying eccentricity.
>
>
>
> --
>
> -----   kc5ejk@onramp.net    or  kc5ejk@amsat.org    -----
>
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