The original satellites, XM-1 ("Rock") and XM-2 ("Roll") suffered from a generic design fault on the Boeing 702 series satellite (fogging of the solar panels), which meant that their lifetimes were shortened to approximately six years instead of the design goal of 15 years. To compensate for this flaw, XM-3 ("Rhythm") was launched ahead of its planned schedule on February 28, 2005 and moved into XM-1's previous location of 85° WL. XM-1 was then moved to be co-located with XM-2 at 115° WL, where each satellite operated only one transponder (thus broadcasting half the bandwidth each) to conserve energy and cut the power consumption in half while XM-4 ("Blues") was readied for launch. Subsequently, XM launched ground-spare XM-4 ("Blues") ahead of schedule on October 30, 2006 into the 115° WL location to complete the satellite replacement program. On December 15, 2006, XM-1 was finally powered down and then drifted back to its original location at 85° WL, where it remained as a backup to XM-3. XM-2 was similarly powered down and remained as a backup to XM-4. This makes the current active satellites as XM-3 "Rhythm" and XM-4 "Blues" with two in-orbit spares.