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Monday, November 11, 2013

GPS Navigation Payload Headed in Right Direction

As reported by Space NewsProblems with the Exelis-built navigation payload on the U.S. Air Force’s next generation of positioning, navigation and timing satellites appear to be solved, according to a company spokeswoman.


Gen. William Shelton, commander of Air Force Space Command, said in September that the GPS 3 navigation payload had no firm delivery date due to manufacturing and processing issues. While the payload’s woes had not yet delayed the GPS 3 program schedule, “we’re running right up against our margins,” Shelton said at the time.
Exelis Geospatial Systems of Rochester, N.Y., is developing the GPS 3 system’s main navigation payload, a role it has had from the beginning of the Lockheed Martin-led program. Exelis spokeswoman Jane Khodos told SpaceNews Nov. 6 “the known technical issues have been resolved.”
Khodos said the navigation payload for the first GPS 3 satellite has been built and is currently being tested with an expected delivery sometime in spring 2014. 
The “navigation payload delays have been driven by first-time development and integration issues, including design changes to eliminate signal crosstalk,” she said. Crosstalk occurs when a signal is broadcast on one circuit and creates an undesired effect on another circuit. GPS 3 will carry a new civil signal that is designed to work with other international global navigation satellite systems.
“GPS 3 will meet all mission and quality requirements,” Khodos said. “Lockheed Martin and Exelis are taking every step necessary to execute successfully, and are rigorously testing the first space vehicle navigation payload to ensure the quality of the GPS 3 design.” 
Denver-based Lockheed Martin Space Systems is the prime contractor on GPS 3, which will feature improved accuracy and better resistance to jamming and other forms of interference than previous generations of GPS craft. Currently the Air Force has eight GPS 3 satellites either fully or partially under contract with Lockheed Martin, and the service earlier this year signaled its intent to order another 12 from the incumbent contractor. But Shelton has said the GPS-3 program’s future is a “question mark,” and that the service may look to try out “alternative architectures” for space-based navigation. 
In December 2012, Exelis announced it had integrated and performed initial testing of a payload aboard a prototype GPS 3 satellite.
The GPS 3 satellites currently are slated to start launching in 2015.
Meanwhile, Exelis announced Nov. 4 that software used to simulate the behavior of GPS signals in space and better understand the satellites’ exact position, completed factory testing. The system will be used as part of the GPS Operational Control Segment (OCX), built by Raytheon Intelligence and Information Systems of Aurora, Colo.
The OCX is expected to support the GPS 3 constellation’s stringent accuracy, anti-jam and information assurance requirements. The system also will be backward compatible with the current generation of GPS satellites.