After many years of planning, tracking data from six National Geospatial-Intelligence Agency (NGA, formerly the National Imagery and Mapping Agency) GPS monitor stations were recently added to the data from the U.S. Air Force monitor station network to generate the real-time operational orbits for GPS. NGA is feeding its monitor station data in real-time to the GPS Master Control Station (MCS) at Schriever Air Force Base in Colorado where they are input to the Kalman filter that ultimately produces the broadcast navigation message.
From August 18 to September 7, NGA data from Washington, DC, England, Argentina, Ecuador, Bahrain and Australia have been systematically added to the routine data processing at the MCS. These stations complement the Air Force stations in Colorado, Florida, Hawaii, Kwajalein, Ascension, and Diego Garcia.
The combined 12-station network will allow satellite operators to see every satellite in the 29-satellite GPS constellation continuously from at least two stations. (When five more NGA sites are added in the future, the MCS will see every satellite from at least three stations.) This will also greatly improve satellite integrity monitoring at the MCS.
Inclusion of the NGA monitor stations is the third phase of a five-phase process. During the first two phases, operational software and modeling were improved. Phase 4, which is slated to begin Sept. 12, will test the MCS backup facility in Gaithersburg, Maryland. Phase 5 will be a follow-on modeling upgrade. Civilian users should see a 15-20 percent improvement in real-time navigational accuracy due to the improved accuracy of the broadcast ephemeris and clock data resulting from the additional stations and improved modeling.