I stand corrected on the XM sat. The Sirius though is not a geo stationary like we use for sat TV. Sirius does not as yet use geostationary satellites, though plans to expand their network in 2008 will add one. Currently, its three LS-1300 satellites fly in geosynchronous highly elliptical orbit in a 24-hour orbital period. Sirius claims the elliptical path of its satellite constellation ensures that each satellite spends about 16 hours a day over the continental United States, with at least one satellite over the country at all times. Sirius completed its three-satellite constellation on November 30, 2000. A fourth satellite remains on the ground in Palo Alto, California as a spare ready to be launched if any of the three active satellites encounter transmission problems.