SVN23/PRN32 to be Set to Healthy

February 7, 2008

The U.S. military announced earlier this week that GPS satellite SVN23, transmitting L-band code as PRN32, will be set to usable status on Feb. 19.

GPS receivers initially were built to accommodate up to 31 satellite signals, and a PRN designated with the number 32 can't be tracked by some manufacturers' devices that look for PRNs numbered 0 through 31. The U.S. Air Force began testing the PRN32 designation late in 2006 — while SVN23/PRN32 was set to unhealthy and not included in the operational GPS constellation almanac, some all-in-view GNSS tracking stations received the L-band signal.

As of January 2007, SVN23 has been broadcasting but set to unhealthy and not included in the almanac. Nevertheless, a number of civilian users have reported being able to track PRN32 since then.

The setting of satellite SVN23/PRN32 to healthy is also notable because in GPS satellite terms, it's coming back from the dead, or at least from decommissioning. It is the first Block IIA satellite, launched on Nov. 26, 1990, and initially decommissioned on Feb.13, 2004, after more than 13 years of service. Apparently the U.S. Air Force reactivated it at some point and set it to broadcast a non-standard code that could not be tracked by standard GPS receivers. However, on Dec. 2, 2006, it started to transmit the standard PRN32 code as part of the Air Force's initial test.

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