[amsat-bb] Re: How to add Moon Keps to SatPC32

mlengruesser@aol.com mlengruesser at aol.com
Tue Feb 23 01:36:54 PST 2010

Hi Laurent,

Attention: The Moon TLE (2line) it's not usefull for the "SGP4/8 two lines format ephemerid model "
(InstantTrack, SatPC32 etc. )
the format is only a compress readable parameters
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. 
73, de Michael 

More information about the AMSAT-BB mailing list