Orbit ephemeris monitors for local area differential GPS

Methodologies sufficient to monitor GPS satellite orbit ephemeris for category I aircraft precision approach navigation are described. In the absence of a satellite maneuver, it is shown that a monitor based on the projection of previously validated ephemeris parameters is adequate to meet navigation integrity and availability requirements. After scheduled stationkeeping maneuvers, no previously validated ephemerides are available, so a measurement-based method is required. The feasibility of such a monitor is also established.