Electro-optical imaging operational high resolution version of Yantar studied in 1969. A draft project was completed in May 1977, but the decision was made to keep the basic Yantar-2K satellite bus instead, resulting in the Yantar-4KS1 reconnaissance satellite.

Flight trials of the Yantar-2K indicated the satellite was not capable of providing strategic warning of attack. The planned Yantar-6K series, in development since 1969, were overweight and behind schedule. A meeting of the Council of Chief Designers at TsSKB reviewed alternative approaches. It was decided that three variants of the Yantar-2K were to be developed, one of them the high resolution Yantar-4K.

• 69 - Sorokin, Vladislav, Novosti Kosmonavtiki, "'Yantarnaya istoriya'", 1997, Issue 17, page 57.
• 110 - Grahn, Sven, Sven Grahn's Space History Pages, . HTML when accessed: http://www.users.wineasy.se/svengrahn/
• 445 - Melnik, T G, Voenno-Kosmicheskiy Siliy, Nauka, Moscow, 1997..
• 451 - Sorokin, V, Novosti kosmonavtiki, "Yantarnaya istoriya-2", No. 11, 1999, p. 71..