US-K

TheUS-K spacecraft are the high-elliptical-orbit component of thesoviet/Russian Oko and Oko-1 early warning systems.

A US-K spacecraft consists of three main subsystems: engine block, device compartment,and optical compartment. All the systems are mounted on a cylindrical frame that is 2 mlong and has diameter of 1.7 m. Total mass of a satellite at launch is estimated to be2400 kg, of which 1250 kg is dry mass. The engine compartment of an Oko satellite includesfuel and oxidizer tanks, four orbit correction liquid-fuel engines and 16 orientation andstabilization liquid-fuel engines. The stabilization engines provide active 3-axisattitude control, necessary for telescope orientation.

The telescope system of a first-generation satellite includes a telescope with a mirrorof about 50 cm diameter. The detection system includes a linear or matrix infrared-bandsolid-state sensor that detects radiation from missiles. In addition to this, thesatellite has several smaller telescopes that most likely provide a wide-angle view of theEarth in infrared and visible parts of spectrum, which is used by operators of the systemas an auxiliary observation channel. The satellite transmits the images formed by itstelescopes directly to the ground control station in real time.

Launches of early-warning satellites into highly elliptical orbits are performed byMolniya-M launchers from the Plesetsk launch site in the northern Russia.

In the beginning of the program, there were serious problems with reliability of thesatellites. Of the first 13 satellites, launched in 1972–1979, only seven worked morethan 100 days. The satellites were equipped with a self-destruct package that wasactivated if the satellite lost communication with ground control. Until these packageswere removed in 1983, 11 out of 31 satellites were destroyed that way.

Some first-generation satellites were launched into geosynchronous orbit by the Protonlaunchers under the designationUS-KS. These launches, which wereconducted from the Baykonur launch site, were all successful.

The choice of observation geometry and of the highly elliptical orbits has been usuallyattributed to the lack of proper infrared sensors and data processing capabilities thatare required for obtaining a look-down capability. According to this logic, in the absenceof suitable sensors, the Soviet Union had to rely on a the grazing-angle observationgeometry, which allowed the use of less sophisticated sensors than those used by theUnited States.

The system was configured in such a way that a satellite would be placed into an orbitthat had inclination of about 63 degrees. The orbits have apogees of about 39,700 km andperigees of about 600 km. A satellite on this orbit has orbital period of approximately718 minutes, and makes exactly two revolutions a day.

Since one satellite can be in a position that allows it to detect missile launches onlyfor about six hours a day, providing 24-hour coverage of the U.S. ICBM bases requires atleast four working satellites. The system, however, was designed to include up to ninesatellites simultaneously. Satellites in the constellation were placed into one of nineorbital planes, which were separated by about 40 degrees from each other.

One reason the system was designed to include satellites in nine separate orbitalplanes was to increase its reliability and to make sure that a loss of one satellite wouldnot create a gap in coverage. A more important reason, however, was that the chosenconfiguration made it possible for several satellites to observe the same areasimultaneously. The advantage of this is that simultaneous observation is that it reducesthe chances that all the satellites that are in a position to detect a launch could besimultaneously blinded by direct sunlight or reflections off clouds.

Beginning in 1984, the constellation of HEO early warning satellites was complementedby satellites in geosynchronous orbit. Satellites that were placed into geosynchronousorbit were the same first-generation satellites that were deployed in highly ellipticalorbits. A satellite placed into the point with longitude of 24 degrees on geosynchronousorbit would see missile launches from U.S. territory at exactly the same angles as an HEOsatellite during the working part of its orbit. In addition, a geosynchronous satellitehas the advantage of not changing its position relative to the Earth, so one satellite canprovide continuous backup of the HEO constellation.

The introduction of geostationary satellites made the system considerably more robust,for it became much more tolerant to a loss of HEO satellites. As was already discussed,without the GEO satellite the system cannot provide continuous coverage of the U.S.territory with fewer than four satellites. With the GEO satellite present, the systemcould still detect launches even if there are no HEO satellites deployed. The quality ofcoverage may suffer and detection may not be reliable enough, but the system would not becompletely blind.

The first satellite that was placed into the highly elliptical orbit characteristic ofthe early-warning satellites was Kosmos-520, launched on 19 September 1972. The exactnature of its mission is unclear, since there are not enough data to see if the satelliteperformed any maneuvers or orbit corrections, but it was reported to be a success.

In the following three years there were four more launches on highly-elliptical orbits,all of which seem to have been experimental. In addition to this, the Soviet Unionconducted an experimental launch of one of the early warning satellites, Kosmos-775, intoa geostationary orbit.

Beginning in 1977, the Soviet Union undertook a series of launches that seemed to be aneffort to built a working prototype of the early warning system. In contrast with previouslaunches, which sometimes placed satellites into non-standard orbits, in the series thatbegan in 1977 satellites were placed into orbits that would allow them to work together.The resulting constellation was still experimental, for the satellites were deployed onorbits in such a way that their groundtracks were shifted about 30 degrees westward fromthe position that will later become nominal. The satellites in those orbits could notdetect launches from operational ICBM bases. Most likely they were observing test launchesof U.S. missiles from the Vandenberg Air Force base, since they would be able to see themunder observation conditions that were very similar to the nominal ones.

Judging by the history of deployment, the prototype system was to include foursatellites that would provide the minimum capability, ensuring that at least one satellitewas in a position to detect a launch at any given moment. However, because of the seriesof malfunctions and failures, it was not until 1980 that the number of working satellitesreached four.

In 1984 the Soviet Union began the program of deploying early warning satellites ingeosynchronous orbit. As discussed above, at that point theseUS-KSsatellites were the same first-generation satellites that were deployed inhighly-elliptical orbits and that were limited to the grazing-angle observation geometry.Nevertheless, deployment of these satellites in geosynchronous orbit must havesignificantly increased the overall reliability of the system.

The first operational early-warning satellite in geosynchronous orbit was Kosmos-1546.In May 1984 it reached the point with longitude of 24 degrees west from which it was ableto detect launches of U.S. ICBMs.

Launch Sites:

• Pl =   Plesetsk (NIIP-53, GIK-1, GNIIP), USSR / Russia   

References:

• P. Podvig: History and the current status of the Russian early warning system, Science and Global Security, Vol. 10, No. 1 (2002)

• US-K
• US-KMO
• US-KS

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