The upcoming replacement of the GPS ground control segment has been successfully rehearsed to ensure a seamless transition next month, commanders of the Air Force Space and Missile Systems Center (SMC) said during an Aug. 15 media briefing on the transition.

The control segment determines the orbital position of GPS satellites and keeps the system operational. The new control segment, called the Architecture Evolution Plan (AEP), will replace the legacy system that has been in use since the 1970s. The upgrade is intended to increase efficiency and provide a foundation for the next generation of GPS satellites.

“The GPS transition team established the model for acquisition and operations working together to bring on new capability without impacting our worldwide users,” said SMC Commander Lt. Gen. Michael Hamel, who

likened the transition to changing the engine on a car while it is traveling 50 miles per hour

down the road.

The upgrade is expected to take four to six days and cost roughly $800 million. For security reasons

the Air Force will not announce the exact date and time of the transition. However, Air force officials said they would

announce its completion to the public 48 hours after the transition is completed.

The control segment consists

of the Master Control Station at Schriever Air Force Base in Colorado, the Backup Master Control Station in Gaithersburg, Md. and six monitor stations and four ground antennae positioned across the globe.

The transition to the AEP was supposed take place more than five years ago but was delayed due to development issues and changing system requirements.

Col. David Madden, commander of the Air Force GPS Wing, called the transition a “new era of GPS operational capabilities,” adding the unexpected time and money it took to finish the system were needed to ensure position accuracy, signal integrity and user transparency.

John Duddy, Boeing’s GPS program director, trumpeted the obstacles overcome by the nation-wide GPS team that made the new control segment a reality.

“The transition from a mainframe to a distributed architecture is a major step in upgrading and modernizing the current control segment,” Duddy said.

The next-generation U.S. satellite navigation system, known as GPS 3 and slated to begin launching by 2013, will be controlled by a new system called the GPS Operational Control Segment. The Air Force is expected to select two contractors this fall to receive $160 million development contracts for initial work on that

segment. Subsequently, one of the two

will be selected in the second half of 2008 to be the prime contractor.