GPS Satellite Geometry Analysis Tool (GPSGEM)

The purpose of the GPS Satellite Geometry Analysis Tool (GPSGEM) is to evaluate GPS satellite geometry for a given Earth-fixed location or for a provided trajectory. The tool will generate a listing of all satellites in view, the best satellite combination defined by the most optimum Geometric Dilution of Precision (GDOP), the GDOP profile expected if all satellites are available, and the worst-case GDOP profile when one or two satellites are removed from the available constellation. The tool will provide the navigation controller with insight into the expected performance of the GPS constellation, and allow an assessment of the implications to onboard navigation performance for the ascent, orbit, abort, and entry phases of flight.