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Air Force Space Command Continues GPS Modernization

Illustration of the Block 2F satellite.
by Joe Davidson
Space and Missile Systems Center Public Affairs
Los Angeles AFB CA (DOD) Aug 22, 2005
Government officials, representing military and civil interests, recently emphasized the need for continued modernization of the Global Positioning System.

Air Force Space Command is making steady progress to deliver modernized satellites, ground control systems and military-user equipment.

The GPS program continues to develop and field new capabilities for the warfighter and civil users, according to Navstar GPS Joint Program Office officials.

The years following the first and subsequent launches of Block I GPS satellites identified the need for continued development and improvements in the existing system.

The first 11 satellites, launched between 1978 and 1985, demonstrated the value of GPS technology.

These early missions led to the development and launch of a series of operational Block II satellites that included a signal for civilian use, launched in 1989.

Additional Block IIA GPS satellites were launched in the early 1990s to complete the GPS constellation, allowing AFSPC to declare full operational capability on April 27, 1995.

Normally, the GPS constellation consists of 24 satellites and associated operational "spares." The largest number of operational satellites on orbit was 30, achieved November 2004.

Today, efforts by Navstar GPS Joint Program Office, aerospace and industry teams include adding new capabilities and improved service to military and civilian users.

"Ultimately, it's all about how we improve service for military and civilian users around the world," said Col. Allan Ballenger, Navstar GPS Joint Program Office system program director. "Sustainment of the GPS constellation is essential, as is modernization of current and future systems and capabilities."

Approximately eight of the latest Block IIR "replenishment" satellites will be modernized to include a new military code and a second civil signal called L2C. The first IIR-M satellite is scheduled for launch later this year.

The two new signals on the IIR-M satellite will provide reduced vulnerability to interference and will allow for calculation of ionospheric corrections at the user's location.

Additionally, service performance in accuracy, availability, integrity and reliability will be realized.

The follow-on system for the IIR-M will be the IIF "follow-on" satellite. These satellites will have the same capability as the IIR-M, plus add a third civil signal called L5 to support several applications, especially civil aviation.

Later this year, the Navstar GPS Joint Program Office will complete another milestone in providing a valuable service to its military and civilian users.

The GPS team will complete implementation of the Legacy Accuracy Improvement Initiative with the National Geo-Spatial Intelligence Agency and the 50th Space Wing.

This initiative will add six of the agency's monitoring stations, located around the world, into the heart of the GPS Operational Control Segment � operated by the Air Force's 2nd Space Operations Squadron at Schriever Air Force Base, Colo.

This Air Force and National Geo-Spatial Intelligence Agency team effort will result in doubling data collected for use by the GPS Master Control Station.

This data enhances the ability to observe satellite performance, and GPS broadcasted navigation message accuracy will be improved.

These improvements called for by the LAII will apply to all users, resulting in a 15 to 20 percent improvement in navigation accuracy without any change to existing receivers � both military and civil.

The initial six monitoring stations will enable the Master Control Station to see every satellite 100 percent of the time from at least two monitoring stations.

When the remaining five agency sites are added, the Master Control Station will see every satellite 100 percent of the time from at least three monitoring stations.

Looking ahead to its first launch in 2013, the next-generation GPS system � Block IIIA � will introduce new capabilities to meet higher demands of military and civilian users.

Block IIIA offers the opportunity for a crosslinked command and control architecture, allowing the entire GPS constellation to be updated from a single ground station instead of waiting for each satellite to orbit in view of a ground antenna.

This will improve accuracy, integrity and reduce vulnerability of GPS signals. Block IIIA also supports a spot beam antenna that provides resistance to hostile jamming.

Whatever improvements can be made or steps to modernization can be taken, the Navstar GPS JPO ensures that United States and allied military and civilian users all over the world will benefit, said Colonel Ballenger.

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