The U.S. Department of Transportation's Civil GPS Service has designated NOAA to be the federal agency responsible for providing accurate and timely Global Positioning System (GPS) satellite ephemerides ("orbits") to the general public. The GPS precise orbits are derived using 24 hour data segments from the global GPS network coordinated by the International Geodynamics GPS Service (IGS). the reference frame used in the computation is the International Earth Rotation Service Terrestrial Reference Frame (ITRF). In addition, an informational summary file is provided to document the computation and to convey relevant information about the observed satellites, such as maneuvers or maintenance. The NGS Precise orbits generally are available seven days after the date of observation.
When the orbit is complete it is submitted to the International GPS Service (IGS) for inclusion into its final product, the IGS Precise Orbit. This precise orbit is considered the International standard and should be used when there is a need for a precise orbit. Since this final product is a combination of several orbit production centers around the globe, it does lag behind in its availability until all centers have reported in. Also, it is not made available until a full GPS week has been completed. For example, Sunday through Friday's orbits will not be made available until Saturday's orbit is ready. The IGS also supplies the Rapid Orbit available the next day and the Ultra Rapid Orbit which is available every 12 hours.
NOAA's Forecast Systems Lab (GPS derived precipitable water vapor)
U.S. Coast Guard's Navigation Center
U.S. Naval Observatory's GPS Data & Information
Univ. of California's Scripps Orbit and Permanent Array Center
Southern California Integrated GPS Network
Jet Propulsion Lab
International GPS Service
Goddard Space Flight Center's Crustal Dynamics Data Information System
Canadian Active Control System
International Earth Rotation Service (IERS)
University NAVSTAR Consortium (UNAVCO)
Geography and Environment Gateway (GEsource)
Physical Sciences Information Gateway (PSIgate)
Orbiteers
Bill Kass