In 1979, NASA's Jet Propulsion Laboratory began planning TOPEX, an Ocean Topography Experiment that would use a satellite altimeter to measure the surface of the world's oceans. At the same time the French space agency CNES was designing an oceanographic mission called Poseidon, named for the Greek god of the sea.
Ariane 42 P T/P launch vehicle The two space agencies decided on a cooperative effort and pooled their resources to form a single mission. The result is the highly-successful TOPEX/Poseidon which has achieved science objectives beyond expectation and at a lower cost than either mission would have achieved separately.
The Ariane 42P carrying the TOPEX/Poseidon spacecraft was launched from the European Space Agency's Guiana Space Center in Kourou, French Guiana, on August 10, 1992.