The World Geodetic System (WGS) is a standard for use in cartography, geodesy, and navigation including by GPS. It comprises a standard coordinate system for the Earth, a standard spheroidal reference surface (the datum or reference ellipsoid) for raw altitude data, and a gravitational equipotential surface (the geoid) that defines the nominal sea level.

The latest revision is WGS 84 (aka WGS 1984, EPSG:4326), established in 1984 and last revised in 2004. Earlier schemes included WGS 72, WGS 66, and WGS 60. WGS 84 is the reference coordinate system used by the Global Positioning System.

Main parameters

The coordinate origin of WGS 84 is meant to be located at the Earth's center of mass; the error is believed to be less than 2 cm.

The WGS 84 meridian of zero longitude is the IERS Reference Meridian, 5.31 arc seconds or 102.5 metres (336.3 ft) east of the Greenwich meridian at the latitude of the Royal Observatory.

The WGS 84 datum surface is an oblate spheroid (ellipsoid) with major (equatorial) radius a = 6378137 m at the equator and flattening f = 1/298.257223563. The polar semi-minor axis b then equals a times (1−f), or 6356752.3142 m.

USA-195, or Wideband Global Satcom 1 (WGS-1) is an American military communications satellite operated by the United States Air Force as part of the Wideband Global Satcom programme. Launched in 2007, it was the first WGS satellite to reach orbit. It is stationed at a longitude of 174.8° east.

Built by Boeing, USA-195 is based on the BSS-702 satellite bus. It had a mass at launch of 5,987 kilograms (13,199 lb), and was expected to operate for fourteen years. The spacecraft is equipped with two solar arrays to generate power for its communications payload, which consists of cross-band X and Ka band transponders. Propulsion is provided by an R-4D-15 apogee motor, with four XIPS-25 ion engines for stationkeeping.

USA-195 was launched by United Launch Alliance, who placed it into orbit using an Atlas V rocket flying in the 421 configuration. The launch took place from Space Launch Complex 41 at the Cape Canaveral Air Force Station, with liftoff occurring at 00:22 UTC on 11 October 2007. The launch was successful, placing the satellite into a geosynchronous transfer orbit, from which the spacecraft raised itself into geostationary orbit using its onboard propulsion systems. The satellite was designated USA-195 under the US military's designation system, and received the International Designator 2007-046A and Satellite Catalog Number 32258.

USA-204, or Wideband Global Satcom 2 (WGS-2) is an American military communications satellite which is operated by the United States Air Force as part of the Wideband Global Satcom programme. Launched in 2009, it was the second WGS satellite to reach orbit, and operates in geostationary orbit at a longitude of 60° east.

Built by Boeing, WGS-2 is based on the BSS-702 satellite bus. It had a mass at launch of 5,987 kilograms (13,199 lb), and was expected to operate for at least fourteen years. The spacecraft is equipped with two solar arrays to generate power for its communications payload, which consists of cross-band X and Ka band transponders. Propulsion is provided by an R-4D-15 apogee motor, with four XIPS-25 ion engines for stationkeeping.

USA-204 was launched by United Launch Alliance, using an Atlas V 421 rocket. The launch occurred from Space Launch Complex 41 at the Cape Canaveral Air Force Station at 00:31:00 UTC on 4 April 2009, and successfully placed the satellite into a geosynchronous transfer orbit, from which the it raised itself into geostationary orbit using its onboard propulsion system. The satellite was designated USA-204 under the US military's designation system, and received the International Designator 2009-017A and Satellite Catalog Number 34713.