Second generation reconnaisance satellites

In 1964 there were two possible paths for the development of Soviet reconnaisance satellites, either modernizing systems based on Zenit-2 and Zenit-4 by concentrating on the camera ssytem and its support subsystems, or to design a new spacecraft with. Actually, both paths were taken. In 1964 the Kuibyshev branch of OKB-1 began draft work on the modernization of the Zenit class of spacecraft. Two new systems were developed:

• For area survey reconnaisance a model of Zenit-2 called 11F690 Zenit-2M (taken into service in 1970 under the code name Gektor). The special reconnaisance system Ftor-2 was replaced by the more capable system Ftor-2R3.
• For high-resolution reconnaisance the 11F691 Zenit-4M (put into service in 1970 under the code name Rotor) with photo-apparatus Ftor-6 replace Zenit-4 and its system Ftor-4.