Serpukhov (Russian: Серпухов; IPA: [ˈsʲɛrpʊxəf]) is a city in Moscow Oblast, Russia, located at the confluence of the Oka and the Nara Rivers, 99 kilometers (62 mi) south from Moscow on the Moscow—Simferopol highway. The Moscow—Tula railway passes through Serpukhov. Population: 127,041 (2010 Census); 131,097 (2002 Census); 143,618 (1989 Census).
Serpukhov was established in 1339 to protect the southern approaches to Moscow. Two years later it was made a seat of the powerful princedom ruled by a cousin and close associate of Dmitry Donskoy, Vladimir the Bold. Town status was granted to it in 1374. The princedom continued until 1456, when the last prince escaped to Lithuania. The town frequently fell prey to the hordes of Tokhtamysh, Crimean Tatars, and other steppe conquerors. It was necessary to protect it with a stone citadel, or kremlin, which was completed by 1556 as part of the Great Abatis Belt.
Within the framework of administrative divisions, Serpukhov serves as the administrative center of Serpukhovsky District, even though it is not a part of it. As an administrative division, it is incorporated separately as Serpukhov City Under Oblast Jurisdiction—an administrative unit with the status equal to that of the districts. As a municipal division, Serpukhov City Under Oblast Jurisdiction is incorporated as Serpukhov Urban Okrug.
Serpukhov-15 (Russian: Серпухов-15) is a military townlet near Kurilovo in Kaluga Oblast which is the location of the western control centre for Russia's Oko satellites. These give early warning of ballistic missile launches, mainly from the continental United States. The site is part of the Main Centre for Missile Attack Warning and information from here is processed at the Russian Aerospace Defence Forces centre in Solnechnogorsk and could be used, together with early warning radar such as the Voronezh, for launch on warning or the A-135 anti-ballistic missile system. A similar facility is located at Pivan-1 in the Russian Far East.
The name Serpukhov-15 is a code name following the practice established to name closed cities and military facilities. It is named after the nearest city, Serpukhov in Moscow Oblast which is about 35 kilometres (22 mi) away.
Oko consists of two types of early warning satellites - US-K and US-KMO. The older US-K satellites are in highly elliptical molniya orbits which give them coverage of the United States at certain times during the day. For full coverage of the US missile grounds four US-K satellites need to be operational and the system can have up to nine of them in orbit at once. The US-KMO satellites are geosynchronous satellites providing continuous coverage. In total, 101 satellites have been launched.