US-KS

Upravlyaemy Sputnik Kontinentalny Statsionarny (Управляемый Спутник Континентальный Стационарный meaning Stationary Continental Controllable Satellite), or US-KS (УС-КС), also known as Oko-S (Око-С meaning Eye-S), was a series of Soviet, and later Russian, missile detection satellites launched as part of the Oko programme. US-KS was a derivative of the US-K satellite, optimised for operations in geosynchronous orbit. Seven were launched between 1975 and 1997, when launches ended in favour of the modernised US-KMO. US-KS had the GRAU index 74Kh6.

Manufactured by NPO Lavochkin, US-KS satellites had a launch mass of 2400 kg, and a dry mass of 1250 kg. Based around a three-axis stabilised cylindrical bus with a diameter of 1.7 m and a length of 2 m, the satellites carry 50 cm infrared telescopes to detect the heat of missile exhausts.

US-KS satellites were launched by Proton-K carrier rockets, with Blok DM and DM-2 upper stages. The first satellite to be launched was a prototype, which was followed by six operational spacecraft. With a spacecraft positioned at a longitude of 24° West, the Soviet Union could continuously monitor missile launches from the United States.