TOPEX/Poseidon is a co-operative 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 stabilised (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 minimise 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 vapour along the path viewed by the altimeter to correct the altimeter data for pulse delay due to water vapour. 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.
Design Life: 3 to 5 years . Total Mass: 2,402 kg.
Ocean sensing, mapping. Spacecraft engaged in research and exploration of the upper atmosphere or outer space (US Cat B).