US-KS (satellite)

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It has been suggested that Oko be merged into this article or section. (Discuss)

The US-KS Oko (Eye) is the primary Soviet early warning satellite, tasked with the detection of rocket launches from the continental United States. The system entered service in the early 1980s and served as the primary Soviet early-warning system into the 1990s. It was originally intended that they would be replaced by the second-generation US-KMO, but these proved to be completely unreliable. With no suitable replacement available, US-KS remains in operation today, although a limited number of satellites are still operational and there are questions about the remaining network's efficiency.

The US-KS system is responsible for a major nuclear false alarm. Shortly after midnight Moscow time on 26 September 1983, the autumn equinox, one of the US-KS satellites reported several US ICBMs being launched. The satellite reports were passed to the Serpukhov-15 bunker outside Moscow, where Stanislav Petrov was in command at the time. Examining the reports, Petrov was convinced the reports were in error, and refused to report the "launches" to his superiors. As he later explained, "when people start a war, they don't start it with only five missiles."^[1] Later study suggests that the angle between the sun, the satellite and the missile fields resulted in reflections off high-altitude clouds that caused the reports. Geoffrey Forden published a report for the Cato Institute that identifies Kosmos-1382 as the most likely culprit for the false alarm.^[2]

[edit] Description

Published images of the US-KS show a cylindrical main body 2 m long and 1.7 m in diameter.^[3] The rear of the main body contains a large engine compartment and fuel tanks, which supplies both the four orbit-keeping engines and the sixteen pointing thrusters. About half of the satellite's estimated 2400 kg launch weight is fuel. On the front is a sunshield made up of a number of concentric boxes that are extended on-orbit to form a conical structure, similar to a folding cup. Solar panels extend from opposite sides of the cylinder.

The telescope system has a main mirror of about 50 cm diameter focusing on an infrared detector. In addition to this, the satellite has several smaller telescopes that most likely provide a wide-angle view of the Earth in both infrared and visible.

[edit] History

Development of the US-KS appears to have started in the late 1960s, some time after the US started its similar Vela program. The satellites are designed and built by NPO Lavochkin. The first experimental launch was Kosmos-520 on 19 September 1972, which was placed in a Molniya orbit. Four similar launches were made over the next three years, all using the Molniya-M rocket launched from the Plesetsk Cosmodrome in northern Russia. One additional launch, Kosmos-775, placed an identical satellite in geostationary orbit instead, using a Proton rocket launched from the Baikonur Cosmodrome.

Activities accelerated sharply in 1977 when a series of eight additional US-KS launches started, all of them into the Molniya orbits. These had their apogee positioned to provide maximum visibility over the west coast of the USA, which made them less useful for observing the US ICBM fields. It is believed these satellites were positioned to observe launches from Vandenberg Air Force Base, using these as a test of both the satellites and the communications channels needed to support them.

Following these test launches, additional satellites were placed into similar orbits with their apogee moved about 30 east, locating them to observe the US missile fields. A full set of four was not operational until 1980 due to satellite failures and other problems. As the system was expanded with additional satellites, the constellation was arranged with nine orbital planes, which were separated by about 40 degrees from each other.

Both series of launches demonstrated an extremely short lifetime for the satellites. Of the first thirteen satellites launched between 1972 and 1979, only seven worked more than 100 days. The satellites were equipped with a self-destruct system that was activated if the satellite lost communication with ground control, and until these devices were removed in 1983, eleven out of thirty-one satellites launched up to that point were destroyed that way.^[3]

The use of Molniya orbits as opposed to geostationary is believed to be due to low sensor effectiveness.^[3] Shortly after launch, as the missile rises above the horizon, the rocket plume is silhouetted against the blackness of space, maximizing the contrast.^[1] From a geostationary position the sun will sometimes appear "behind" the satellite, leading to potential blinding due to atmospheric reflections. In the Molniya orbits the satellite is much farther north with a larger angle between the sun and the satellite. The downside of this approach is that each satellite spends about six hours in a useful position over the US, meaning that four satellites are required for 24-hour coverage.

Starting in 1984 with Kosmos-1546 the main Molniya launches were supplemented by operational geostationary ones as well, positioned off the west coast of Africa to give a similarly large "grazing angle" as the Molniya positions. Molniya and geostationary launches continued at a rapid pace between 1980 and 1993 with an average of five launches a year, but this slowed dramatically after this period and since then there have been only about one launch a year. It appears modern versions of the satellite have dramatically improved lifetimes of about four years,^[4] which may explain the slower launch cycle. However it is also possible this is due to the lower strategic threat of the US, combined with budgetary pressures. One source states that there are only two working satellites as of 2007 (one Molniya, one geostationary),^[4] but NASA currently lists four.^[5]

To date, in 2007, there have been a total of 88 US-KS launches.