Title of Paper: The Development and Demonstration of NASA's Global Differential System


Principal Author: Dr. Yoaz Bar-Sever


Abstract: We will describe the development, demonstration, and applications of the NASA Global Differential GPS (GDGPS) system, an effort that is funded under the Advanced Information Systems Technology (AIST) Program. The system is intended to provide end-to-end capabilities for autonomous, real-time orbit determination and positioning with an unprecedented level of accuracy. The system relies on a reference network that is a real-time subset of NASA's Global GPS Network (GGN), consisting of geodetic quality dual-frequency receivers. The GGN network implements a novel internet-based technology for editing and real-time streaming of data as input to real-time GPS orbit determination software running at the operations center. A novel internet-based architecture provides for multiply-redundant operation centers, leading to enhanced reliability while maintaining cost-efficiency. Real time corrections to the GPS orbits and clocks are broadcasted using geosynchronous communication satellites leased by a commercial partner, and are available globally as well as in space. The user employs special hardware to receive the differential correction messages and special software to combine that information with data from a GPS receiver, and provide highly accurate estimates of position or orbital state in real time. Ground tests have demonstrated 10 cm horizontal positioning accuracy and 20 cm vertical positioning accuracy in real time. Simulations demonstrated 5 cm 3D RMS real time orbit determination accuracy for a Topex-like satellite. We will describe some of the Earth science, civilian, and commercial applications that will benefits from this new technology.