NGS Emblem      Precise Orbits NOAA Logo
U.S. DEPARTMENT OF COMMERCE | National Oceanic and Atmospheric Administration | National Ocean Service

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.


  1. GPS Naming Convention
  2. Information
  3. Analysis Strategy Summary
  4. NGS Rapid Orbits (1 day latency)
  5. Precise Orbits
    • NGS Precise Orbits (~  8 day latency)
      Warning - the EF18 Binary file (E18) may come down corrupted if using Netscape 4.77 or older.  The older versions of Netscape do not recognize it as a binary file.
      • constrained with 6 hour overlap on each end - sp3, e18, sum
      • this file was the one uploaded to the USCG Navcen
      • file named by year, month and day
    • IGS Precise Orbits (~ 15 day latency)
      • minimally constrained 24 hour file - sp3
      • file named by GPS Week Number
      • ultra rapid available here
  6. Orbit Utilities
  7. SP3 Format
  8. GPS Calendar
  9. USCG Navigation Center


GPS Links:

GPS Bibliographies
National Geodetic Survey's Continuously Operating Reference Stations (CORS)
Related Geodetic Resources
Transform between height systems with GEOID99

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
Bob Dulaney


Back To:
CORS | NGS | NOS | NOAA | U.S. Dept. of Commerce


anim earth National Geodetic Survey - Don Haw
Last modified: November 29, 2002
http://www.ngs.noaa.gov/GPS/GPS.html