US-K
Upravlyaemy Sputnik Kontinentalny (US-K; Russian: Управляемый Спутник Континентальный meaning Continental Controllable Satellite; Russian: УС-К) is a series of Russian, previously Soviet, satellites used to detect missile launches as part of the Oko system. It consists of a constellation of satellites, usually in molniya orbits, designated under the Kosmos system.