NGA's Role in GPS

B. Wiley, D. Craig, D. Manning, J. Novak, R. Taylor, L. Weingarth

Abstract:	NGA and its predecessor organizations have operated Global Positioning System (GPS) Monitor Stations for more than 20 years. The NGA GPS Monitor Station Network (MSN) supports the DoD reference system WGS 84 and has expanded to include direct support to the Air Force (AF) Operational Control Segment (OCS). NGA stations are located around the world, strategically placed to complement the more equatorial Air Force Monitor Stations. These stations use geodetic quality GPS receivers and high performance cesium clocks. NGA monitors the behavior of its stations remotely to ensure their data integrity and high rate of availability. The NGA GPS stations are tightly configured and controlled to achieve the highest accuracy possible. NGA plays a vital role in GPS integrity monitoring. Since Sep 2005, the AF GPS Master Control Station (MCS) Kalman filter has used data from NGA GPS Monitor Stations to determine the broadcast orbits of the GPS satellites. NGA data also gives the MCS visibility of the satellites from at least two stations at all times. Sending NGA data to the MCS in near real time has enhanced both the accuracy and integrity of GPS. The computation of the GPS Precise Ephemeris, which is considered DoD truth, is an integral part of supporting WGS 84. The ephemeris, computed using NGA, AF and a few International GNSS Service (IGS) stations, is provided to the AF and posted on NGA’s website for all GPS users. This paper discusses the NGA GPS Monitor Station Network configuration and performance. Station clock stability analysis demonstrates that NGA exceeds industry standards. The history of the NGA GPS precise orbit and clock estimates shows steady improvement. A comparison of NGA’s GPS Precise Ephemeris is made to that of IGS showing increased consistency between the two over time.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	2111 - 2119
Cite this article:	Wiley, B., Craig, D., Manning, D., Novak, J., Taylor, R., Weingarth, L., "NGA's Role in GPS," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 2111-2119.
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