[IGSMAIL-5209]: National Geospatial-Intelligence Agency GPS Monitor Station Data Now Included in U.S. Air Force GPS Operational Orbits

[Slater, James A.]

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IGS Electronic Mail      09 Sep 10:45:50 PDT 2005      Message Number 5209
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Author: Jim Slater
Dear Colleagues:
This is an informational update on GPS operations that I thought might be of
general interest.  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.

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James A. Slater                    National Geospatial-Intelligence Agency
Tel: 703-735-3944                  Basic and Applied Research Office (IB),
Mail Stop DN-11
Fax: 703-735-3960                 12310 Sunrise Valley Drive
slaterj at nga.mil                     Reston, VA 20191-3449                 
"To steal ideas from one person is plagiarism; to steal from many is
research." (Anon.)