Magnum was a class of SIGINT spy satellites reportedly operated by the National Reconnaissance Office (NRO) for the United States Central Intelligence Agency (CIA).
[1] According to Jim Slade of ABC News, the second satellite, USA-48, replaced the first, USA-8, which after more than four years in orbit was running out of maneuvering fuel required for keeping its station over the Indian Ocean.
The mission of the two satellites was to listen in to military and diplomatic communications from the Soviet Union, China, and neighboring countries.
[2] USA-67, launched aboard Space Shuttle Atlantis (OV-104) in November 1990 (STS-38 mission), was initially identified as a third Magnum satellite owing to the presence of two upper stages in orbit after its deployment, suggesting that an Inertial Upper Stage (IUS) had been used to deploy it.
[3][4] The Magnum satellites, built by TRW, are rumored to have large (estimated 100 m (330 ft) diameter)[5][6] umbrella-like reflecting dishes to collect RF signals from Earth.