Missile Attack Warning Systems (SPRN)

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).

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. 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.