Geosat
U.S. Navy satellite for gravity field and oceanography.
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The U.S. Navy launched GEOSAT, a GEOdetic SATellite, on March 12, 1985. It orbited at 800 km with a 108-degree inclination. Its radar altimeter measured sea surface distance to within about 5 cm. After a classified initial Geodetic Mission, the satellite shifted to an oceanographic Exact Repeat Mission.
Mission
Geosat's Geodetic Mission sought to map the marine gravity field. The ocean surface, if undisturbed, follows the geoid, which is shaped by gravity variations from underwater mountains and trenches. Measuring the ocean's height relative to Earth's center reveals the geoid, from which the gravity field is calculated.
Exact Repeat Mission
After the Geodetic Mission concluded on September 30, 1986, GEOSAT's Exact Repeat Mission began on November 8, 1986, following maneuvers into a 17.05 day, 244 pass exact repeat orbit. This orbit was more favorable for oceanographic applications, allowing observation of water level changes caused by currents, tides, and wind forcing, with typical features having amplitudes around 20 cm. The satellite was actively controlled to maintain the ground track within 1 km. The ERM ended in January 1990 due to failure of the two on-board tape recorders, after collecting more than three years of data made available to the scientific community.
Declassification
The U.S. Navy declassified parts of the Geodetic Mission data in 1990 covering a doughnut-shaped area of ocean surrounding Antarctica between 60 and 72 degrees south latitude. In 1992, further data over oceans south of 30 degrees south were released. The entire global sea surface data was declassified in July 1995 after the completion of the geodetic phase of the ESA ERS-1 mission, and subsequently used to estimate ocean bathymetry.
GFO
The Geosat Follow-On mission launched on February 10, 1998 aboard a Taurus rocket from Vandenberg AFB. It carried a water vapor radiometer and a radar altimeter, operating in the same orbit as GEOSAT's Exact Repeat Mission, along with a GPS receiver (never used operationally), Doppler receivers, and laser retro-reflectors. GFO was scheduled for retirement on December 31, 2008, but due to spacecraft deterioration, controllers lowered it to a disposal orbit and shut it down on November 25, 2008. A planned GFO-2 mission with a dual-band altimeter was cancelled by the U.S. Navy on June 30, 2010.
More in Military Space Program of the United States
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Geosat (CC BY-SA 4.0).
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