For this joint mission, the National Aeronautics and Space Administration (NASA) is providing the satellite bus and five instruments with their associated ground elements. NASA's Jet Propulsion Laboratory is responsible for project management, and will operate and control the satellite through NASA's Tracking and Data Relay Satellite System. The Centre National d'Etudes Spatiales (CNES) is furnishing two instruments with their associated ground elements and a dedicated launch on an Ariane rocket. Both CNES and NASA will provide precision orbit determination and will process and distribute data to 38 science investigators from nine nations, as well as other interested scientists.

In the summer of 1992, TOPEX/Poseidon will be launched into orbit by an Ariane rocket from the European Space Agency's Space Center located in Kourou, French Guiana. From its orbit 830 miles (1,336 kilometers) above the Earth's surface, TOPEX/Poseidon will make sea level measurements along the same path every 10 days using the dual frequency altimeter developed by NASA and the CNES single frequency solid-state altimeter. This information will be used to relate changes in ocean currents with atmospheric and climate patterns. Measurements from NASA's Microwave Radiometer will provide estimates of the total water-vapor content in the atmosphere, which will be used to correct errors in the altimeter measurements. These combined measurements will allow scientists to chart the height of the seas across ocean basins with an accuracy of 5 inches (13 centimeters).

Three independent techniques will determine the satellite altitude within 4 inches (10 centimeters). NASA's Laser Retroreflector Array will be used with a network of 10 to 15 satellite laser ranging stations to provide the baseline tracking data for precision orbit determination and calibration of the radar altimeter bias. The DORIS system, recently demonstrated by the French SPOT-2 mission, will provide an alternate set of tracking data using microwave Doppler techniques. The system is composed of an onboard receiver and a network of 40 to 50 ground transmitting stations, providing all-weather, global tracking of the satellite. NASA's Global Positioning System Demonstration Receiver will demonstrate a new technique for precise, continuous tracking of the spacecraft.

TOPEX/Poseidon is a vital part of a strategic research effort to explore ocean circulation and its interaction with the atmosphere. It is timed to coincide with and complement a number of international oceanographic and meteorological programs, including the World Circulation Experiment (WOCE) and the Tropical Ocean and Global Atmosphere (TOGA) Program, both of which are sponsored by the World Climate Research Program (WCRP). TOPEX/Poseidon is a three-year mission with the potential for a two-year extension. Results from TOPEX/ Poseidon will build the foundation for a continuing program of long-term observations of ocean circulation from space, and for an extensive ocean monitoring program in the next century.