US-PM (Upravlenniye Sputnik Passivny Modifikirovanny) (also reported as US-PU) was a
solar powered improved EORSAT (Electronic Ocean Reconnaissance Satellite). It used an
passive ELINT devices to track naval vessels from space by registering their electronic
emmissions.
US-PM was a modified version of the US-P and replaced both the US-P and the nuclear US-A satellites.
It shared the same US bus with its precedessors, which provided maneuvering
capabilities to the spacecraft.
The satellites were built by the KB Arsenal design bureau in Leningrad/St.-Petersburg, and the payloads by the Central Scientific Radiotechnical Research Institute or TsNIRTI in Moscow.
The US-PM were placed into a 420 km orbits inclined 65 degrees by the Tsiklon-2 booster. Systems aboard the 3300 kg
satellite included the Radio-Technical Reconnaissance system and systems for electronic
camouflage and self-protection. An engine unit maintained the orbital altitude and made a
final deorbit of the satellite at the end of the mission.
It has been reported, that Kosmos 2421 failed to open one of its eight solar panel
segments after launch.
US-PM will be replaced by the new Pion-NKS ELINT satellites of the Liana system.
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