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Global Differential GPS System
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The NASA GDGPS System was designed to support the most demanding real-time GPS applications, on a global scale, and in space. Below is a partial list of application areas where the GDGPS System has been used operationally.

Data management for High performance GPS tracking networks:

The GDGPS System is being used to operate and control real-time GPS data streaming from a vast global GPS tracking network, including the NASA GGN. Efficient real-time data transfer is enabled through remote data editing and data compression. Strong authentication schemes provide security against data tampering. Local copies of of the collected measurements can be left in-situ to ensure full recovery of precsion geodetic data. The data collected from the GDGPS network is shared with the scientific community through the archival services of the NASA CDDIS facility.

Precise real-time positioning and orbit determination:

Mobile, airborne, and space users can be positioned in real-time with unparalleled accuracy with the User Module of the RTG software, using the precise real-time GPS orbit and clock products of the GDGPS System. The GDGPS System has been used to provide operational positioning and orbit determination services to the following NASA missions and projects:

  • Rapid orbit determination for the Shuttle Radar Topography Mission (SRTM)
  • Rapid orbit determination for the Jason-1 mission for the generation of near-real-time sea surface products
  • Real-time onboard positioning for the AirSAR DC-8 for payload checkout and calibrations
  • Real-time onboard positioning for the UAV-SAR G-3 airplane for autonomous repeat path control

GPS performance monitoring and situational assessment:

Since the GDGPS System determines the real-time state of the GPS contellation with unparalleled accuracy, we can assess the performance of the system, in absolute terms, and relative to its broadcast navigation message. From monitoring the integrity of the GPS constellation, to situational awareness for theaters of operations, to the support of critical operations world-wide, GDGPS has the unrivalled ability to assess the performance of the GPS navigation signals in real-time.

Real-time environmental monitoring:

The NASA Deep Space Netork (DSN) uses near-real-time tropospheric delay estimates based on GDGPS real-time GPS orbit and clock states to calibrate the radio signals from deep space spacecraft in support of deep space navigation. Real-time global ionospheric total electron content (TEC) maps are derived at JPL and by the Air Force Weather Agency (AFWA) base on GDGPS tracking data.

Commercial differential systems:

The GDGPS System produces differential corrections to the GPS broadcast ephemeris with unparelleled accuracy and seamless global validity. Various GDGPS technology components and data products are being used by nearly all of the providers of premium global differential corrections. The underlying software and algorithms are being used by the FAA's Wide Area Augmentation System (WAAS), and its Japanese counterpart, MSAS.

Assisted GPS data services:

Any and all A-GPS data are available from the GDGPS System in support of the E911 mandate and various other telecommunications and positioning applications. Complete global coverage, and extremely high reliability resulting from the high level of system redundancy, provide unparalleled value for wireless carriers and GPS chip makers seeking high-performance A-GPS services in support of their mobile devices.

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