|Country of origin||Russia|
|Operator||Russian Aerospace Defence Forces|
|Applications||Early warning of missile attack|
EKS (reportedly standing for Russian: Единая космическая система, tr. Edinaya Kosmicheskaya Sistema meaning Unified Space System) is a future programme of Russian early warning satellites and a replacement for the US-KMO and US-K satellites of the Oko programme.:7 These satellites identify ballistic missile launches from outer space and complement early warning radars such as the Voronezh. This gives advance notice of a nuclear attack and would provide information to the A-135 missile defence system which protects Moscow.
Information on the new EKS system is scarce but it appears that it was designed by Energia Corp in 1999-2000 and was selected against a proposal from Oko manufacturer NPO Lavochkin. The Russian Ministry of Defence awarded the contract to Energia in 2007 with an expected delivery date of 2008, for a test launch in 2009. In 2009 it was reported to be delayed until late 2011/early 2012. In 2011 the Russian MoD sued Energia for the delay, claiming that a contract extension issued until May 2010 was invalid and asking for 262 million rubles in compensation. According to news reports Energia said that the contract extension was valid and that the problem was with their subcontractors. In addition they said that the Russian MoD kept changing the specification and demanding things that were beyond the capabilities of the industry. The Russian MoD lost the court case. Energia delivered a satellite in 2009 but as of April 2012 there has not been a test launch.
In April 2012 minister Alexander Sukhorukov announced that a contract had been signed to manufacture these satellites and that there would be a launch later in 2012. The last satellites of the previous Oko system were Kosmos 2479, launched on 30 March 2012, and Kosmos 2469, launched on 30 September 2010.
EKS is designed as a replacement for the current system of early warning satellites called Oko, which had its first launch in 1972 :36 and was described in 2005 as "hopelessly outdated". Oko has two types of satellites: US-KMO are in geosynchronous orbits and have an infrared telescope to identify ballistic missile launches. US-K are in molniya orbits and are an earlier model with optical telescopes and infrared sensors. The Oko system has two control centres with the main one being Serpukhov-15 outside Moscow. :40:52
In 2014 Kommersant published that the first satellite, of a type named Tundra, would be launched in 2014. According to that report they would operate on highly elliptical orbits. The satellite was not launched in 2014, however. 
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- Pavel, Podvig (2014-07-19). "New-generation early-warning satellite, Tundra, to be launched in 2014". Russian Strategic Nuclear Forces. Retrieved 2015-02-10.