Zenit is the name of a series of military spy satellite

Spy satellite

A spy satellite is an Earth observation satellite or communications satellite deployed for military or intelligence applications....

s launched by the Soviet Union

Soviet Union

The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 between 1961 and 1994. To conceal their nature, all flights were given the public Kosmos

Cosmos (satellite)

Kosmos is a designation given to a large number of satellites operated by the Soviet Union and subsequently Russia. Kosmos 1, the first spacecraft to be given a Kosmos designation, was launched on March 16, 1962....

 designation. Over a 33 year period, over five hundred Zenits were flown making it the most numerous type of satellite in the history of spaceflight.

Description

The basic design of the Zenit satellites was similar to the Vostok

Vostok spacecraft

The Vostok was a type of spacecraft built by the Soviet Union. The first human spaceflight in history was accomplished on this spacecraft on April 12, 1961, by Soviet cosmonaut Yuri Gagarin....

 manned spacecraft. It consisted of a spherical re-entry capsule 2.3 m in diameter with a mass of around 2400 kg. 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 5 m and the total mass was between 4600 kg and 6300 kg.

Unlike the American Corona

Corona (satellite)

The Corona program was a series of American strategic reconnaissance satellites produced and operated by the Central Intelligence Agency Directorate of Science & Technology with substantial assistance from the U.S. Air Force...

 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 weight of the satellite. An advantage was that cameras could be reused.

Early Zenits were launched using the Vostok rocket

Vostok rocket

Vostok was a family of rockets derived from the Soviet R-7 Semyorka ICBM designed for the human spaceflight programme. This family of rockets launched the first artificial satellite and the first manned spacecraft in human history...

; later versions used the Voskhod

Voskhod rocket

The Voskhod rocket was a derivative of the Soviet R-7 ICBM designed for the human spaceflight programme but later used for launching Zenit reconnaissance satellites. It combined the R-7 with an upper stage that had been originally designed to launch interplanetary probes.There was only one main...

 and the Soyuz rockets. The first flights were launched from the Baikonur Cosmodrome

Baikonur Cosmodrome

The Baikonur Cosmodrome , also called Tyuratam, is the world's first and largest operational space launch facility. It is located in the desert steppe of Kazakhstan, about east of the Aral Sea, north of the Syr Darya river, near Tyuratam railway station, at 90 meters above sea level...

 but subsequent launches also took place at the Plesetsk Cosmodrome

Plesetsk Cosmodrome

Plesetsk Cosmodrome is a Russian spaceport, located in Arkhangelsk Oblast, about 800 km north of Moscow and approximately 200 km south of Arkhangelsk.-Overview:...

.

Most Zenits flew in a slightly elliptical orbit

Orbit

In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...

 with a perigee

Perigee

Perigee is the point at which an object makes its closest approach to the Earth.. Often the term is used in a broader sense to define the point in an orbit where the orbiting body is closest to the body it orbits. The opposite is the apogee, the farthest or highest point.The Greek prefix "peri"...

 of around 200 km and an apogee between 250 km and 350 km; the missions usually lasted between 8 and 15 days.

History

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 3

Sputnik 3 was a Soviet satellite launched on May 15, 1958 from Baikonur cosmodrome by a modified R-7/SS-6 ICBM. It was a research satellite to explore the upper atmosphere and the near space, and carried a large array of instruments for geophysical research....

 (Sputnik 1

Sputnik 1

Sputnik 1 ) was the first artificial satellite to be put into Earth's orbit. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957. The unanticipated announcement of Sputnik 1s success precipitated the Sputnik crisis in the United States and ignited the Space...

 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.

By 1958, the OKB-1

S.P. Korolev Rocket and Space Corporation Energia

OAO S.P. Korolev Rocket and Space Corporation Energia , also known as RKK Energiya, is a Russian manufacturer of spacecraft and space station components...

 design bureau was simultaneously working on Object OD-1 and Object OD-2—an early design for the Vostok

Vostok spacecraft

The Vostok was a type of spacecraft built by the Soviet Union. The first human spaceflight in history was accomplished on this spacecraft on April 12, 1961, by Soviet cosmonaut Yuri Gagarin....

 manned spacecraft. The development of Object OD-1 was experiencing serious difficulties so the head of OKB-1, Sergei Korolev, initiated work to see if a design based on Object OD-2 could be used for an unmanned photo-reconnaissance satellite. This may have been a political manoeuvre that would enable him to continue the manned space program and avoid diverting more of OKB-1’s resources into Object OD-1.

Despite bitter opposition from the military, the Soviet government endorsed Korolov’s approach and issued decrees on 22 May and May 25, 1959 that ordered the development of three different spacecraft, all based on the same basic, Object OD-2, design. Spacecraft 1K would be a simplified prototype, 2K was to be a reconnaissance satellite and 3K was to be for manned flights. The name Vostok was also initially used for all three of these craft. But in 1961 the name became publicly known as the name of Yuri Gagarin

Yuri Gagarin

Yuri Alekseyevich Gagarin was a Soviet pilot and cosmonaut. He was the first human to journey into outer space, when his Vostok spacecraft completed an orbit of the Earth on April 12, 1961....

's spacecraft so the 'Vostok 2' reconnaissance satellite was renamed 'Zenit 2'.

The first Zenit launch attempt took place on 11 November 1961, but there was a fault in the rocket’s third stage and the spacecraft was destroyed using its destruct charge. The second attempt—publicly referred to as Cosmos 4—was successfully launched on the 26 April 1962 and re-entered three days later. However a failure in the orientation system meant no useful pictures were obtained. The third Zenit (Kosmos 7) was launched on the 28 July 1962 and successfully returned with pictures eleven days later. A further ten flights (including two more launch failures) took place before the system was considered operational.

Many versions of the satellite were developed for different reconnaissance missions and flights continued until 1994.

Zenit 2

Zenit 2 was the first version to be launched in 1961 (there was no Zenit 1.)

The arrangement of cameras varied, but most flights carried four cameras of 1000 mm focal length, and one of 200 mm focal length. The single lower resolution camera was intended to provide low-resolution pictures that would help give a context to the high-resolution pictures.

Each camera had 1500 frames of film and from 200 km, each frame held an image of a 60 km by 60 km square. The ground resolution was stated to be 10–15 m although some unofficial sources claim it was much better—one source claims the number of cars in a car park could be counted. The cameras were developed at the Krasnogorsk

Krasnogorsk, Moscow Oblast

Krasnogorsk is a city and the administrative center of Krasnogorsky District of Moscow Oblast, Russia, adjacent to the northwestern boundary of Moscow, on the Moskva River...

 Optical-Mechanical factory near Moscow

Moscow

Moscow is the capital, the most populous city, and the most populous federal subject of Russia. The city is a major political, economic, cultural, scientific, religious, financial, educational, and transportation centre of Russia and the continent...

. Curiously, this was also where the popular Zenit SLR cameras

Zenit (camera)

Zenit is a Russian camera brand manufactured by KMZ in the town of Krasnogorsk near Moscow since 1952 and by BelOMO in Belarus since the 1970s. The Zenit trademark is associated with 35mm SLR cameras...

 were made.

Zenit 2s also carried ELINT equipment to receive NATO radar signals. The satellites carried a parabolic antenna

Parabolic antenna

A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish...

, around 1 meter in diameter, that is associated with this equipment. However, it is unclear if the antenna transmitted recorded signals to the ground or was for intercepting radar signals. In the latter case they would have been recorded on magnetic tape, to be retrieved after the return capsule landed.

There were 81 Zenit 2 launches, 58 were successful and 11 were partially successful. There were 12 failed missions, 5 because of a satellite malfunction and 7 because of a failure in the launch vehicle.

First flight - Kosmos 4, 1962. Last flight - Kosmos 344, 1970.

Zenit 2M

Improvements included a new camera system and the addition of solar panels. As the spacecraft mass was increased to 6300 kg, the Vostok rocket was replaced by the Voskhod and Soyuz rockets.

First flight - Kosmos 208, 1968. Last flight - Kosmos 1044, 1978.

Zenit 4

Unlike Zenit 2, little information on Zenit 4 has been released. The Zenit 4 was intended for high resolution photography and carried one camera of 3000 mm focal length as well as a 200 mm camera. The focal length of the main camera was greater than the diameter of the capsule so the camera made use of a mirror to fold the light path. The ground resolution is not publicly known but it is believed to have been 1–2 m.

The Zenit 4 weighed 6300 kg—around 1500 kg more than the Zenit 2. So, instead of the Vostok rocket, it was launched by the heavier Voskhod rocket. A probable total of 76 Zenit 4’s were flown.

First flight - Kosmos 22, 1963. Last flight - Kosmos 355, 1970.

Zenit 4 M

An improved version of the Zenit 4, the Zenit 4M carried a new camera, solar panels, and a restartable engine so the satellite’s orbit could be altered during the course of its mission. Mission duration was 13 days.

First flight - Kosmos 251, 1968. Last flight - Kosmos 667, 1974.

Zenit 4 MK / Zenit 4 MKM

These may have been versions of the Zenit 4 designed specifically to fly in lower orbits to improve image resolution. Some sources claim they were fitted with devices to compensate for aerodynamic drag and to withstand the effects of aerodynamic heating

Aerodynamic heating

Aerodynamic heating is the heating of a solid body produced by the passage of fluid over a body such as a meteor, missile, or airplane. It is a form of forced convection in that the flow field is created by forces beyond those associated with the thermal processes...

.

First flight - Kosmos 371, 1970. Last flight - Kosmos 1214, 1980.

Zenit 4 MT

A special version of the Zenit 4M intended for topographical

Topography

Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...

 photography. It carried a SA-106 topographic camera, a laser altimeter and Doppler apparatus.

First flight - Kosmos 470, 1971. Last flight - Kosmos 1398, 1982.

Zenit 6U

A ‘universal’ version of the Zenit, intended for both low-altitude, high-resolution missions and higher-altitude, general observation missions. All flights used the Soyuz launch vehicle. There were 96 launches.

First flight - Kosmos 867, 1976. Last flight - Kosmos 1685, 1985.

Zenit 8

This was intended for military cartographic

Cartography

Cartography is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.The fundamental problems of traditional cartography are to:*Set the map's...

 photography. It used a Soyuz launch vehicle and launches took place from both Baikonur and Plesetsk. It had a 15 day orbital life. Similar satellites were referred to using the ‘Resurs’ designation.

Kosmos 2281, was the last Zenit flight.

First flight - Kosmos 1571, 1984. Last flight - Kosmos 2281, 1994.

Following the end of the programme, one Zenit-8 satellite was launched on the maiden flight of the Soyuz-2 rocket, as a DemoSat

DemoSat

A DemoSat is a boilerplate spacecraft used to test a carrier rocket without risking a real satellite on the launch. They are most commonly flown on the maiden flights of rockets, but have also been flown on return-to-flight missions after launch failures...

. The satellite was placed on a sub-orbital trajectory, and intentionally impacted the Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

shortly after launch.

External links

• Complete Zenit Chronology
• Zenit at astronautix.com