RE: trouble plotting geosat with SkyMap

From: Matson, Robert (
Date: Wed Nov 12 2003 - 14:10:50 EST

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    Hi Thomas,
    > I used to
    > pick out GOES 6, as a geosynchronous satellite that I should be
    > able to observe.  However, when I tried to plot its location using
    > SkyMap 6.6 (which I recently got to run on my Windows XP system,
    > after seeing some SeeSat-L posts a while back), it showed it
    > trucking right along, about like the HST.
    Sounds like you may have loaded the two-line elements for
    GOES 6 R/B (#14051) or (less likely) the GOES 6 apogee kick motor
    (#14069) instead of GOES 6 itself (#14050).
    > Does anybody know what the problem is (I noted that SkyMap doesn't
    > explicitly list the SGDP model, but only SGP4), ...
    SkyMap uses MSGP4 -- so-called "merged" SGP4.  This uses SGP4 for
    low altitude satellites and SDP4 for high altitude ones.  The dividing
    line on which model is used is the orbital period -- anything with a
    period greater than 225 minutes gets handled by SDP4.  --Rob
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