EORSAT (ELINT Ocean Reconnaissance Satellite)
Ground-based image of an EORSAT spacecraft.
EORSAT (ELINT Ocean Reconnaissance Satellite) is a system of specialized Russian/Soviet ELINT (electronic intelligence) satellites that became operational in 1978 following an initial launch in 1974. It monitored and located enemy naval forces by detecting and triangulating on their radio and radar emissions. Each EORSAT consisted of a 3,1500-kilogram spacecraft with a 1.3-meter diameter, 17.0-meter-long cylindrical bus and two large solar arrays. A typical operational orbit was 404 kilometers by 417 kilometers at an inclination of 65°. About 45 EORSAT spacecraft had been launched, by Tsylon 2 rockets from Baikonur, by the end of 2001.