Bruno wrote: >I wonder anyway how USSPACECOM measure positions of satellites which are >not visible from the US or any US possession. There are several references to GEODSS if you search yahoo. Here are two: http://www.spacecom.af.mil/usspace/geodss.htm http://www.fas.org/spp/military/program/track/geodss.htm The site at Diego Garcia is responsible for getting confused and tracking the wrong object for the last few months. (IMO) (It's a Brittish territory.) We had a former GEODSS operator tell us a little about it when he found us using my 16-inch to track a few objects at a recent "dark sky" star party. He said the computer points the telescope at the predicted place and they manually control the center of the CCD display from the object to a nearby star and back again about 3 or 4 times. When the target object or star is centered, they push a button to tell the computer to save the current position. After getting a few positions on one object, they go to the next object. Mike