This excerpt taken from the SIRI 10-Q filed Nov 12, 2008.
Loss or premature degradation of XMs existing satellites could damage its business.
XM placed its XM-3 and XM-4 satellites into service during the second quarter of 2005 and fourth quarter of 2006, respectively. XMs XM-1 and XM-2 satellites experienced progressive degradation problems common to early Boeing 702 class satellites and now serve as in-orbit spares. An operational failure or loss of XM-3 or XM-4 would, at least temporarily, affect the quality of XMs service, and could interrupt the continuation of its service and harm its business. XM likely would not be able to complete and launch its XM-5 satellite before September 2009. In the event of any satellite failure prior to that time, XM would need to rely on its back-up satellites, XM-1 and XM-2. There can be no assurance that restoring service through XM-1 and XM-2 would allow XM to maintain adequate broadcast signal strength through the in-service date of XM-5, particularly if XM-1 or XM-2 were to suffer unanticipated additional performance degradation or experience an operational failure.
A number of other factors could decrease the useful lives of XMs satellites, including:
In addition, XMs network of terrestrial repeaters communicates principally with one satellite. If the satellite communicating with the repeater network fails unexpectedly, XM would have to activate its backup satellites (XM-1 and XM-2) to restore repeater service. This would result in a degradation of service that could last several hours or longer and could harm XMs business.