TOPEX / Poseidon

TOPEX/Poseidon is a cooperative mission between the United States and France designed to provide high-accuracy global sea level measurements. Data from TOPEX/Poseidon is used to map ocean circulation patterns, help understand how the oceans interact with the atmosphere, and improve our ability to predict the global climate. NASA provided the satellite bus, five instruments, and is responsible for spacecraft operations. CNES furnished two of the spacecraft's instruments and the mission's Ariane launch vehicle. During its first 3 years on orbit, the satellite measured sea heights to within 4 cm.

Spacecraft
Based on Fairchild Multi-Mission Spacecraft bus. 3-axis stabilized (nadir pointing) via reaction wheels and torque rods. Attitude determination via Earth sensors, Sun sensors, star cameras, IRU, magnetometers. Single solar array with 1-axis articulation provides 3400W (BOL). 3 50 A-hr batteries. 1.2 m HGA for communications via TDRSS. Hydrazine propellant system for orbit maintenance. GPS antenna mounted on deployed boom to minimize multipath noise.

Payload
Dual frequency altimeter (C- and Ku-Band) measures the height of the satellite above the sea. TOPEX Microwave Radiometer (TMR) measures the water vapor along the path viewed by the altimeter to correct the altimeter data for pulse delay due to water vapor. Single-frequency Solid-State Altimeter (SSALT) operates at 13.65 GHz (Ku-Band) to measure the height of the satellite above the sea, wind speed, and wave height. The Laser Reflector Array (LRA) is used with ground-based lasers to track the satellite and to calibrate and verify altimeter measurements. A GPS receiver is used to provide precise orbit ephemeris data. DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) is also used for precise orbit determination, as well as to receive signals from ground stations for satellite tracking, make gravity field measurements, and provide ionospheric correction data for SSALT.

Country of Origin	United States, France
Customer/User	NASA, JPL, CNES
Manufacturer(s)	JPL, Fairchild, Alcatel
Orbit	1336 km circular, 66 deg inclination, with 10 day repeat
Design Life	3 to 5 years
Related Sites	JPL Topex Summary Page JPL Topex Project Home Page GSFC Topex Home Page Jennifer Green's Topex Page

Launch Facts

Name	Int'l Desig.	Date	Site	Vehicle	Orbit	Mass(kg)
Notes
TOPEX-Poseidon	1992-052A	8/10/92	Kourou	Ariane 42P	LEO	2402
Ocean sensing, mapping