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 Bruno_Tilgner@compuserve.com