Zenit (satellite)

Zenit (Зени́т, zjɪˈnjit, Zenith) was a series of military photoreconnaissance satellites launched by the Soviet Union between 1961 and 1994. To conceal their nature, all flights were given the public Kosmos designation. The basic design of the Zenit satellites was similar to the Vostok manned spacecraft, sharing the return and service modules. It consisted of a spherical re-entry capsule in diameter with a mass of around . This capsule contained the camera system, its film, recovery beacons, parachutes and a destruct charge. In orbit, this was attached to a service module that contained batteries, electronic equipment, an orientation system and a liquid-fuelled rocket engine that would slow the Zenit for re-entry, before the service module detached. The total length in orbit was around and the total mass was between . Unlike the American CORONA spacecraft, the return capsule carried both the film and the cameras and kept them in a temperature-controlled pressurised environment. This simplified the design and engineering of the camera system but added considerably to the mass of the satellite. An advantage was that cameras could be reused. The camera would either land on the ground or be recovered in midair by a modified Mil Mi-8 helicopter. Early Zenits were launched using the Vostok rocket; later versions used the Voskhod and the Soyuz rockets. The first flights were launched from Baikonur Cosmodrome but subsequent launches also took place at Plesetsk Cosmodrome. Most Zenits flew in a slightly elliptical orbit with a perigee of around and an apogee between ; the missions usually lasted between 8 and 15 days. In 1956, the Soviet government issued a secret decree that authorised the development of "Object D" which led to the program to launch Sputnik 3 (Sputnik 1 was a simplified spin-off of the Object D program.) The text of the decree remains secret, but it apparently authorised another satellite program – "Object OD-1" – which was to be used for photo-reconnaissance from space.