A NASA satellite, the first to use synthetic aperture radar (SAR) for remote sensing of the Earth's oceans. It was launched in June 1978 with a scheduled mission of up to three years. However, its electric power system failed in October after sending only about 42 hours of data.

Seasat was to have measured the sea surface winds and temperatures, wave heights, internal waves, and water in the atmosphere, and investigate sea ice and ocean topography. Despite its failure, the mission successfully demonstrated the use of microwave sensors to monitor the seas.