Geosat The GEOSAT ( GEOdetic SATellite ) was a U . S . Navy Earth observation satellite , launched on March 12 , 1985 into an 800 km , 108° inclination orbit , with an orbital period of 23 . 07 days and a 330 pass orbit . The satellite carried a radar altimeter capable of measuring the distance from the satellite to sea surface with a relative precision of about 5 cm . The GM mission concluded September 30 , 1986 . After a classified Geodetic Mission ( GM ) for the Navy , GEOSAT ' s scientific Exact Repeat Mission ( ERM ) began on November 8 , 1986 after being maneuvered into a 17 . 05 day , 244 pass repeat orbit . When the ERM ended in January 1990 , due to failure of the two on - board tape recorders , more than three years of ERM data were collected and made available to the scientific community . The Geosat GM goal was to provide information on the marine gravity field . If the ocean surface were at rest , and to forcing such as tides or winds were acting on it , the water surface would lie along the geoid . To first order , the Earth shape is an oblate spheroid . Subsurface features such as seamount s create a gravitational pull , and features such as ocean trenches create lower gravity areas . Spatial variations in gravity exert influence on the ocean surface and thereby cause spatial structure in the geoid . The deviations of the geoid from the first order spheroid are on the order of ± 100m . By measuring the position of the water surface above the Earth center , the geoid is observed , and the gravity field can be computed through inverse calculations . The U . S . Navy declassified parts of the Geodetic Mission data in 1990 that covered a doughnut - shaped area of ocean that surrounds Antarctica between 60 and 72 degrees south latitude . In 1992 , further parts of the Geodetic Mission data over the oceans south of 30 degrees south were released . The GEOSAT data for the entire global sea surface was declassified in July 1995 after the competition of the geodetic phase of ESA ERS - 1 mission . These data were subsequently widely used to estimate ocean bathymetry along with additional satellite altimeters . Once the GM goal had been reached , the satellite still had a useful life . An opportunity existed to observe the next order physical process that affects the ocean surface . Currents , tides and wind forcing all create changes in water levels . While there are extreme waves and events ( tsunamis and hurricane surge ) , typical ocean features would be considered large if the water level change caused by them were 1 m . Most areas of the world experience features of typical amplitude of 20 cm . The ERM established the satellite in an exact repeat orbit . The satellite would orbit the Earth , and after 17 . 05 days the satellite would return to the same point . The satellite was actively controlled through thrust maneuvers to maintain the exact repeat orbit to within 1 km of the predefined ground track . In this manner , the satellite could observe long term changes at the points along the ground track . GFO . The successor to GEOSAT is the Geosat Follow - On ( GFO ) mission , launched 1998 - 02 - 10 by a Taurus rocket from Vandenberg AFB . GFO carried a water vapor radiometer as well as a radar altimeter , and operated in the same orbit as GEOSAT ' s Exact Repeat Mission . In addition , GFO carried a GPS receiver ( which was never used operationally ) , Doppler receivers , and laser retro - reflectors for orbit determination . GFO was scheduled for retirement on December 31 , 2008 , but in late September 2008 , the deteriorating state of the spacecraft resulted in a decision to accelerate the shutdown . Despite a series of system failures aboard the spacecraft , controllers were able to successfully lower GFO and Robert Pack to a disposal orbit and shut it down on November 25 , 2008 . The next satellite in the series , named GFO - 2 , is planned for launch in 2014 , and will feature a dual - band altimeter , instead of the single - band altimeter on the previous spacecraft .