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As of 15 August 2023[update], 83 Global Positioning System navigation satellites have been built: 31 are launched and operational, 4 are unhealthy or in reserve, 41 are retired, 2 were lost during launch, and 1 prototype was never launched. 4 Block III satellites have completed construction and have been declared "Available For Launch" (AFL). The next launch is GPS III SV07, scheduled for June 2024.
The constellation requires a minimum of 24 operational satellites, and allows for up to 32; typically, 31 are operational at any one time. A GPS receiver needs four satellites to work out its position in three dimensions.[1]
SVNs are "space vehicle numbers" which are serial numbers assigned to each GPS satellite. PRNs are the "pseudo-random noise" sequences, or Gold codes, that each satellite transmits to differentiate itself from other satellites in the active constellation.
After being launched, GPS satellites enter a period of testing before their signals are set to "Healthy". During normal operations, certain signals may be set to "Unhealthy" to accommodate updates or testing. After decommissioning, most GPS satellites become on-orbit spares and may be recommissioned if needed. Permanently retired satellites are sent to a higher, less congested disposal orbit where their fuel is vented, batteries are intentionally depleted and communication is switched off.[2]
- ^ US Government. "GPS.gov". gps.gov. U.S. Government. Retrieved 21 March 2015.
This article incorporates text from this source, which is in the public domain.
- ^ "2 SOPS disposes last GPS IIA satellite after 26 years". GPS World. 17 April 2020. Retrieved 7 July 2021.
