GEONS

The GPS-Enhanced Orbit Navigation System, GEODE, is a NASA-developed software package that improves the accuracy of GPS-generated three-dimensional position and velocity fixes. GEODE means true orbit determination -- not just positioning with GPS. In simulations using NASA satellite data, GEODE-filtered GPS data produced position accuracies to better than 20 meters -- a five-fold increase over most commericial receivers – and velocity measurements to better than 0.03 meters per second (both results are 1 sigma).

Many spacecraft have orbit and/or attitude constraints that limit how much of the GPS constellation they can see, making traditional "point solution" GPS system innaccurate or unusable during periods when less than four GPS satellites are in view. Understanding this problem, the GEODE development team, led by the Flight Dynamics Analysis Branch at NASA's Goddard Space Flight Center, built their software with enough robustness to continue to generate quality navigational products with fewer than four GPS satellites in view. Simulations show that GEODE is so robust that it can function even after losing view of the entire GPS constellation.

Click Here [http://nmdb.gsfc.nasa.gov/geons] for details on GEONS as well as license information.