Zenit (satellite)

: "For other uses, see Zenit (disambiguation)."

Zenit ( _ru. Зени́т, "Zenith") is the name of a series of military spy satellites launched by the Soviet Union between 1961 and 1994. To conceal their nature, all flights were given the public Kosmos 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 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 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; later versions used the Voskhod and the Soyuz rockets. The first flights were launched from the Baikonur Cosmodrome but subsequent launches also took place at the Plesetsk Cosmodrome.

Most Zenits flew in a slightly elliptical orbit with a perigee 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 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.

By 1958, the OKB-1 design bureau was simultaneously working on Object OD-1 and Object OD-2—an early design for the Vostok 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's spacecraft so the 'Vostok 2' reconnaissance satellite was renamed 'Zenit 2'.

The first Zenit launch attempt took place on the 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 variants

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 Optical-Mechanical factory near Moscow. Curiously, this was also where the popular Zenit SLR cameras were made.

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

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

Zenit 4 MT

A special version of the Zenit 4M intended for topographical 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 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. The satellite was placed on a sub-orbital trajectory, and intentionally impacted the Pacific Ocean shortly after launch. [ [http://www.astronautix.com/lvs/soyuzst.htm Soyuz-ST - Encyclopedoa Astronautica] ]

References

*‘Eye in the Sky: Story of the Corona Spy Satellites’; ed. by Dwayne Day; Smithsonian, 1998.
*Peter A Gorin: "Zenit - The First Soviet Photo-Reconnaissance Satellite", Journal of the British Interplanetry Society, Vol. 50, 1997, pg 441.
*'Korolov' James Harford John Wiley 1997.
*http://www.astronautix.com/index.html
* [http://www.svengrahn.pp.se/histind/Recces/Recces.htm Soviet/Russian reconnaissance satellites page at Sven's Space Place]
* [http://www.skyrocket.de/space/space.html Gunters Space Page]

External links

* [http://www.zarya.info/Diaries/Vostok/Vostok.php Zenit & Vostok - early days]
* [http://www.astronautix.com/craft/zenit.htm Zenit] at astronautix.com