Oko US-KS Missile Attack Warning Systems (SPRN)
The Oko ["Eye"] missile early warning satellites were launched into Molniya orbits. Each satellite carried an explosive charge in order to destroy it in case of a malfunction. Reportedly, the control of this mechanism was unreliable. These vehicles perform missile launch early warning duties in orbits very similar to the Russian Molniya communications payloads. The three-axis stabilized vehicle is cylindrical in shape with two solar array panels and an erectable sun shade for the primary on-board sensor system. Dimensions of the cylinder are approximately 2 m in diameter and 1.7 m in length; dry mass is on the order of 1250 kg.
The development of an integrated early warning system, including a space constellation, began in the USSR in the 1960s. The system was supposed to be built on the following principles: separation, integrated use of the information received, maximum automation of information collection, centralized data collection and management without using the human factor in the field. As a means of detection in the early warning system, two echelons were envisaged: the first space, consisting of a constellation of satellites, and the second ground, represented by over-the-horizon and over-the-horizon radar stations (radars). It was envisaged that the second echelon, in particular, should confirm or deny the data of the first echelon about firing missiles on the territory of the USSR. The pre-operational early warning spacecraft network began in 1976 with Kosmos 862. The Lavochkin NPO-manufactured satellite was initially 1,250 kg with a diameter of 2.0 m and a length of only 1.7 m, excluding the solar arrays and the sensor sun shield. Four years later the transition to a full operational capability with nine satellites in evenly spaced orbital planes was initiated. The constellation comprised the first echelon of the Missile Attack Warning System (SPRN), which was operated by the Air Defense Forces of the Ministry of Defense. According to Soviet officials the early warning satellites could detect missile launches within 20 seconds of lift-off (References 86-91).
The highly elliptical, semi-synchronous orbits result in high altitudes over the Northern Hemisphere where most surveillance sensors are located, Each satellite possessed a perigee of about 600 km, an apogee of nearly 40,000 km, and an inclination of 63 degrees. This orbit was superficially similar to that employed by Molniya communications satellites but was distinguished by initial argument of perigee 316-319 degrees, including to the Molniya 280-288 degree arguments of perigee. The seemingly minor difference significantly affected the shape of the satellite's groundtrack in the Northern Hemisphere.
Russian early warning spacecraft are more affected by gravitational perturbations due to their higher argument of perigee and, therefore, perform periodic station-keeping maneuvers to maintain an acceptable groundtrack. The orbit is a Molniya-like orbitis affected by mean motion resonance of the tesseral terms of the Earth potential, and the secular resonances of the Moon and Sun. In addition, the argument of perigee migrates slightly over time (due to inclination variations), causing an alteration in the shape of the groundtrack. Instead of expending additional propellant to prevent the argument of perigee shift, Russian spacecraft controllers alter the satellite's ascending node. This has the effect of "stabilizing" the apogee point about which surveillance operations are performed.
During 1993-1994 four of the nine operational spacecraft were replaced: Kosmos 2232, Kosmos 2241, and Kosmos 2261 were launched in 1993, followed by the solitary launch of Kosmos 2286 in 1994. At the end of 1994 the early warning constellation appeared to be fully functional with its oldest member (Kosmos 2063) less than five years old. An experimental Oko satellite, Kosmos 2105, completed its mission in 1993. All Oko satellites placed in Molniya-type orbits are launched by the Molniya-M booster from the Plesetsk Cosmodrome.
The system was taken on alert in 1982 - as usual with the military, in December. The constellation consisted of several satellites in highly elliptical orbits to observe the continental United States and one in geostationary orbit. At the initial stage, satellites were used with both infrared telescopes and television equipment. TV equipment ensured effective observation against the background of the night Earth, IR sensors made it possible to monitor launches around the clock.
Nevertheless, both for devices with IR telescopes and for satellites with TV equipment, an operating mode was set in which the launching rocket torch should have been detected precisely against the background of black space, that is, the observation was carried out at a large angle to the launch area. This was done in order to exclude false alarms from other sources of light and heat, which are abundant on earth, water and in the planet's atmosphere, due to the imperfection of the satellite computing system and the limitations of its memory and power. For example: during flight design tests, one of the first SPRN satellites "confused" the launch of a ballistic missile with a Tu-16 bomber flying in the same area.
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