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Re: Moon keps

Once years ago I saw a little DOS utility that would generate lunar Keps 
for standard tracking software.  For best results, the program needed to 
be  run every few days as the moon doesn't behave as near earth orbiting 
objects do and the generated element sets went bad fast.

I saw this program on a BBS called D.R.I.G. in Texas.  I don't know if it's 
around anymore. They had quite a nice selection of astronomical type software.


At 03:29 PM 7/6/01 -0500, Robert Winingham <kc5ejk@earthlink.net> wrote:
>this question comes up often
>type a google search for Moon keps
>like this
>and see
>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.
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