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In June 2011, the Air Force successfully completed a GPS constellation expansion known as the "Expandable 24" configuration. The extra satellites may increase GPS performance but are not considered part of the core constellation. The Space Force normally flies more than 24 GPS satellites to maintain coverage whenever the baseline satellites are serviced or decommissioned.
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This 24-slot arrangement ensures users can view at least four satellites from virtually any point on the planet. Each plane contains four "slots" occupied by baseline satellites. The satellites in the GPS constellation are arranged into six equally-spaced orbital planes surrounding the Earth. Expandable 24-Slot satellite constellation, as defined in the SPS Performance Standard.
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