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As of February 2016, 72 Global Positioning System navigation satellites have been launched; not all remain operational. The minimum number of satellites for a full constellation is 24 operational 95% of the time; the current number exceeds this. The target number is 33 and decommissioned reserves are available to maintain the numbers.
SVNs are "space vehicle numbers", the serial numbers assigned to each GPS satellite, and PRNs are the "pseudo-random noise" sequences, or Gold codes, that each satellite transmits to differentiate itself from other satellites in the active constellation.
Numbers in parentheses refer to non-operational satellites.
Once launched, GPS satellites do not change their plane assignment but slot assignments are somewhat arbitrary and are subject to change.
The following table is for the purpose of making it possible to determine the block associated with a PRN by looking at one column in one table rather than having to search through all rows of three tables. Thus this table can be used to quickly and easily determine the number of satellites in orbit and health associated with each block.
This section is for the purpose of making it possible to determine the PRN associated with a SVN at a particular epoch. For example, SVN 049 had been assigned PRNs 01, 24, 27, and 30 at different times of its lifespan, whereas PRN 01 had been assigned to SVNs 032, 037, 049, 035, and 063 at different epochs. This information can be found in the IGS ANTEX file, which uses the convention "GNN" and "GNNN" for PRNs and SVNs, respectively. For example, SVN 049 is described as:
whereas for PRN 01 the following excerpt is relevant:
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