http://www.gpsworld.com/gnss-system/...y-9641?print=1

GPS Modernization
Ground Control Software Update to AEP 5.50D Set for Friday
March 3, 2010

Building on the January 2010 upgrade to the GPS ground control segment,
on Friday Air Force Space Command will be installing another software
release, AEP 5.5D, primarily designed to support the pending mid-2010
launch of the first GPS IIF space vehicle.

“Unlike the January release, known as Architecture Evolution Plan (AEP)
5.5C, this release, known as 5.5D, does not affect any user interfaces,
and therefore should be transparent to the end user,” said Col. David
Buckman, Chief, Positioning, Navigation and Timing Division, AFSPC
Directorate of Requirements. “To ensure such transparency, the software
upgrade has undergone rigorous testing and will be monitored very
closely by Air Force Space Command to ensure it performs as expected."

"The software upgrade does not modify the content of the broadcast
navigation message and should therefore be transparent to all users. All
testing has been completed for this version of the software and
confidence is very high that it will perform without any change
noticeable to users," said an e-mail notification sent out by Rick
Hamilton, CGSIC Executive Secretariat, USCG Navigation Center.

Hamilton asked for users' help in pinpointing any issues. "We would like
your confirmation on this. If you observe anything unusual in the GPS
constellation or in user GPS equipment operation on the 5th, or during
the following week, please notify NAVCEN (per the
NANU below) as soon as possible."

Civilians experiencing any anomalies should contact the U.S. Coast Guard
Navigation Center at 703-313-5900. Military end users who experience
any anomalies should contact the 50th Space Wing’s GPS Operations Center
(GPSOC) at DSN 560-2541.

“AFSPC has led the charge to improve military and civil navigation
capabilities to ensure GPS remains the gold standard for position,
navigation, and timing service worldwide,” added Col. Buckman. “We are
confident that this improvement initiative will continue the Air Force’s
commitment to the global community of GPS users.”

Below is the Notice Advisory to Navstar Users (NANU) about the upgrade.