||10 August 1992
||Measure sea surface height
The Topex/Poseidon satellite was launched on 10 August 1992 with the objective of "observing and understanding the ocean circulation". A joint project between NASA, the US space agency, and CNESthe French space agency, it carried two radar altimeters and precise orbit determination systems, including the DORIS system.
To be useful for studying ocean circulation, especially on gyre and basin scales, numerous improvements had been made to Topex/Poseidon compared with previous altimetry systems (Seasat, Geosat), including a specially-designed satellite, suite of sensors, satellite tracking systems and orbit configuration, as well as the development of an optimal gravity model for precision orbit determination and a dedicated ground system for mission operations.
Topex/Poseidon laid the foundation for long-term ocean monitoring from Space. Every ten days, it supplied the world's ocean topography, or sea surface height, with unprecedented accuracy.
On 15 September 2002 Topex/Poseidon assumed a new orbit midway between its original ground tracks. The former Topex/Poseidon ground tracks are now overflown by Jason-1. This tandem mission demonstrated the scientific capabilities of a constellation of optimised altimetry satellites. The last data were acquired on October 2005, due to a failure in a pitch reaction wheel. The mission ended on 18 January 2006.