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.