The Oko early-warning satellite system

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The Soviet space-based missile launch detection system, which watched American ICBM fields for the infrared flare of a rocket motor and reported to a ground command centre south of Moscow. Its design reflects a constraint: Soviet satellites used highly elliptical Molniya orbits rather than the geostationary belt, and observed the missile fields obliquely against the edge of the Earth rather than looking straight down at them, which was intended to reduce false alarms from reflected sunlight. It did not eliminate them. On 26 September 1983 the system reported a small American launch, and the cause was subsequently attributed to sunlight reflecting from high cloud in an alignment the sensors had not been designed for. The episode is the clearest documented case of the general problem: an early-warning system exists to compress the time between detection and decision, and compressing that time is exactly what makes a false report dangerous.