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.
Low Earth OrbitThe U.S. Navy began replacing and upgrading its ultra-high frequency (UHF) satellite communications network during the 1990s with a constellation of customized satellites built by Hughes Space and Communications Company. Known as the UFO (Ultra High Frequency Follow On) series, these HS-601 model satellites support the Navy's global communications network, serving ships at sea and a variety of other U.S. military fixed and mobile terminals.
Geostationary OrbitThe Orion 3 and 4 (RIO 3, 4) satellites, which are generally known as 'Advanced Orion' or 'Mentor', are geostationary signals intelligence satellites, which replaced the Magnum / Orion series. Their purpose is to intercept missile telemetry from Russia and China and the COMINT capability of the Mercury satellites was merged into this series. These satellites are launched under the designation Program 7600.
Geostationary Orbit