FUNCTIONAL OVERVIEW

The NASA GDGPS System is driven by a powerful software set, developed completely in-house at JPL, and possessing many unique features and capabilities. The C-language software evolved from one of the world's leading GPS data processing and analysis software packages, JPL's GIPSY-OASIS. The GDGPS software elements have accumulated a remarkable track record of accomplishments, including:

Used as prototype for the FAA's Wide Area Augmentation System (WAAS)

Awarded NASA Software of the Year 2000

Flew in space, embedded in a JPL Blackjack GPS receiver, performing real-time onboard orbit determination, 2002

Inducted into the Space Technology Hall of Fame, 2003

The software is comprised of four primary modules:

1. The RTNT (Real Time Net Transfer) module manages data collection at the tracking site, and performs on-the-fly data editing, data compression, data authentication, and streaming of the packetized data over the communicatins channel to the GOCs. At the GOC this module sorts and decompresses the data from the network of remote sites.

2. The Real Time GIPSY (RTG), System Module is used to process GPS measurements from the global network and derive the real-time orbit and clock estimates for the satellites, as well as estimates of the clock, position, and environmental parameters for the tracking network. The software is also used to derive and format the many other high-level products and by-products of the GDGPS System.

3. The Real Time GIPSY (RTG), User Module is used to perform real-time point-positioning or orbit determination for a single GPS receiver. It is used within the GDGPS system to derive several by-products and to for quality control. It is also offered to users of the GDGPS System who want to extrat maximum accuracy from the GDGPS differential corrections.

4. The Real Time Ionosphere (RTI) module is used to derive global maps of total electron content (TEC), which are used to provide differential corrections to single-frequency users anywhere in the world. Global TEC maps are also a standalone GDGPS product, which is used to monitor space weather and predict ionospheric storms. RTI employs a Kalman filter to combine in time and space the line-of-site integrated electron content from each pair of receiver-satellite.

USABILITY

Complete automation. End-to-end automatic operations.

Complete positioning system. The software handles all aspects of a complete real time global positioing system, including GPS orbit determination and simultaneous network positioing. Embedded, the software performs user positioining and orbit determination.

Highly portable. The software has already been ported to the following systems: VX Works, Linux, Unix, PowerPC, Windows NT, and RogueOS

Versatile. Works with many types of popular geodetic receivers: TurboRogue, Benchmark ACT, Ashtech uZ, Trimble NetRS. Flexible adaptation layer makes it easy to accommodate new receiver types

Visual aids. Real time graphic display of performance using network monitoring tools and internal quality control.

QUALITY FACTORS

ANSI C for portability and maintainability.

Modularity. Highly modular code to support embedded as well as ground applications.

Reliability. Outstanding track record of continnuous operations.

Accuracy. All models are sub-cm accurate for the most demanding science applications.

Maintainability. Designed for operations by a third party and for team maintenance. Configuration control management.

CREATIVITY

• Patented state-space architecture guarantees seamless global uniformity of the differential corrections

• Innovative use of the internet to achieve robustness through redundancy

• Unique satellite dynamics and signal models developed in house at JPL

• Efficient GPS data compression

• Innovative system for end-to-end redundant operations provides critical reliability

• Uniquely flexible filter design allows any parameter to have stochastic attributes

• Capable of adding satellites/receivers on the fly

• Unique dynamics integrator supports light time iterations

• Tropospheric delay model and stochastic estimation capability for users or reference sites

• Exploit full information content of phase data

• Real time playback

Many more innovations contribute to GDGPS's unparalleled performance and unique value.