NORAD model for geostationary satellites

Bruno Tilgner (
Mon, 27 Oct 1997 14:37:15 -0500

Hello everybody,

I have received a number of photos (film or CCD) of the ASTRA cluster
of geostationary satellites, positioned at longitude 19.2 degrees east,
and have tried to reproduce their relative position and motion with
various software tools, including my own.

This has not been successful, neither as regards the topology of the
cluster nor the mouvement of the satellites over periods ranging from
just under 1 hour to up to 10 hours.

Since I suppose virtually all software uses the same NORAD model as
the prediction engine, I begin to have serious doubts about the
applicability of the SDP4 model to geostationary satellites. Hence
this mail.

Has anybody ever confirmed or otherwise, by direct comparison of
observation and prediction, that the SDP4 model gives correct positional
results with an accuracy in the order of 5 arcminutes?

Thanks for any comments.

Bruno Tilgner
Saint-Cloud, France