Cosmos 1805 was a Soviet ELINT (Electronic and Signals Intelligence) satellite launched from the Plesetsk cosmodrome.
From 1965 to 1967 two dedicated ELINT systems were tested: the Tselina and the Navy's US. Both reached service, since the Ministry of Defence could not force a single system on the military services.
Tselina was developed by Yuzhnoye and consisted of two satellites: Tselina-O for general observations and Tselina-D for detailed observations. ELINT systems for Tselina were first tested under the Cosmos designation in 1962 to 1965. The first Tselina-O was launched in 1970. The Tselina-D took a long time to enter service due to delays in payload development and weight growth. The whole Tselina system was not operational until 1976. Constant improvement resulted in Tselina-O being abandoned in 1984 and all systems being put on Tselina-D.
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