2000 Award Winner
Internet-Based Global Differential GPS (IGDG)
Lead NASA Center:
Jet Propulsion Laboratory (JPL)
NPO-19625, 20835, 20976
IGDG (internet –based Global Differential GPS) is a uniquely powerful and flexible c-language software package that provides a complete end-to-end system capability for real-time positioning and orbit determination, with unprecedented accuracy, coverage, and economy. Components of IGDG have been used as the foundation in several critical real-time systems for NASA, other agencies, and the commercial sector. The software promises significant scientific, technological, and economic benefits to NASA, the Nation, and society in general. Specifically, IGDG has demonstrated 10 cm to 30 cm real time positioning to users carrying compatible equipment, anywhere in the world, anytime. No other system is capable of similar performance.. Similarly, IGDG is capable of providing a few centimeters-level real time orbit determination for Earth orbiting satellites. This level of accuracy can currently be achieved only in post-processing mode with latencies of days and weeks. IGDG was developed over several years with funding from the Technology Program of the Telecommunications and Mission Operations Directorate (TMOD) at JPL, the Technology and Applications Program (TAP) at JPL, and from the Solid Earth and Natural Hazard Program of the Office of Earth Science (Code YS). IGDG consists primarily of two modules. The RTNT (Real Time Net Transfer) module on-the-fly collects, edits, and compresses the raw GPS observables at the remote reference site. It then transmits the packetized data over the open internet to the processing center. At the processing center the global data from a network of remote sites (nominally the NASA Global GPS Network (GGN)) is sorted by RTNT. Here, a powerful and unique feature of RTNT allows for multiply redundant operations centers to receive the data over the internet and provide seamless backup in case of failure at the primary operations center, or in its internet connectivity. The GPS data is then analyzed by the real time orbit determination module, RTG (Real Time GIPSY), to produce precise GPS orbits and clocks. These are formatted as corrections to the GPS broadcast ephemerides, encoded, and are provided over the internet to authorized users. A user equipped with a GPS receiver and a facility to receive the correction message will use a local version of RTG to precisely compute its position in real time. RTG includes precise orbital dynamics models to support onboard orbit determination. RTG implements some of the precise measurement algorithms present in the GIPSYOASIS II software package, but is fundamentally different in its architecture, programming language and concept of operations, which are optimized for demanding real time applications and embedded operations.