Just come across this via work, if its already posted I apologise but if not might be of use.
The U.S. Air Force has announced that a major upgrade is planned for the GPS control segment (referred to as the Architecture Evolution Plan, or AEP). AEP will swap out the entire master control station, which uses a 1970s-era legacy system, to a modern design based on current technology. Among other things, this change is required in order to implement new capabilities, such as the next generation of IIF satellites.
The AEP change is scheduled to occur during the second week of September, over a period of 4-6 days. The
transition will phase in a few satellites at a time and will be completely reversible if anything goes wrong. Before it begins, the old and new ground control systems will be synchronized to the millimeter level so that the most demanding users will experience a seamless change.
The civil community has been asked to disseminate the word about the upcoming change as widely as possible. Should any anomalies be detected during the transition period, users should follow the normal notification procedures via the U.S.Coast Guard Navigation Center (www.navcen.uscg.gov
The original file can be found at http://igscb.jpl.nasa.gov/mail/igsma.../msg00103.html