Manned Space Flight Network

The Manned Space Flight Network (abbreviated MSFN, pronounced "misfin") was a set of tracking stations built to support the American Mercury, Gemini, Apollo, and Skylab space programs.

There were two other NASA space communication networks at the time, the Spacecraft Tracking and Data Acquisition Network (STADAN) for tracking unmanned satellites in low Earth orbit, and the Deep Space Network (DSN) for tracking more distant unmanned missions. After the end of Skylab, the MSFN and STADAN were merged to form the Spaceflight Tracking and Data Network (STDN). STDN was in turn replaced by the satellite-based Tracking and Data Relay Satellite System (TDRSS) during the Space Shuttle program, being used as of 2009^[update].

Tracking vehicles in low Earth orbits (LEO) is quite different from tracking deep space missions. Deep space missions are visible for long periods of time from a large portion of the Earth's surface, and so require few stations (the DSN uses only three, as of February 20, 2010^[update]). These few stations, however, require the use of huge antennas and ultra-sensitive receivers to cope with the very distant, weak signals. Low Earth orbit missions, on the other hand, are only visible from a small fraction of the Earth's surface at a time, and the satellites move overhead quickly, which requires a large number of tracking stations, spread all over the world. The antennas required for LEO tracking and communication are not required to be as large as those used for deep space, but they must be able to track quickly.

These differing requirements led NASA to build a number of independent tracking networks, each optimized for its own mission. Prior to the mid-1980s, when the Tracking and Data Relay Satellite System (TDRSS) satellites became operational, NASA used several networks of ground based antennas to track and communicate with Earth orbiting spacecraft. For the Mercury, Gemini, and Apollo missions, these were the primary means of communication, with the Deep Space Network (DSN) being assigned a supporting/backup role.

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