The Satellites plugin simulates artificial satellites in Earth orbit. Satellite orbits could not be predicted precisely enough using Stellarium's existing orbital models for Solar System bodies, as there are other factor involved - irregularities in the Earth's gravitational field, lunar interactions, atmospheric drag and so on. So this plugin implements the SGP4 and SDP4 orbital models, using as its input data in NORAD's two-line element set (TLE) format. Lists with TLEs for hundreds of satellites are available online
and are regularly updated. The plugin downloads the lists prepared by celestrak.com to keep itself up-to-date, but the users can specify other sources online or load updates from local files.
This plugin comes bundled with Stellarium version
0.10.3, although it is not enabled by default. To enable the plugin, open the configuration dialog and go to the plugins tab. Click Satellites from the list of available plugins and check the load at startup checkbox. You will need to re-start Stellarium for changes to take effect.