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USA 77



This US Navy Ocean Surveillance Satellite (NOSS) was launched from Vandenberg AFB aboard a Titan 4 rocket. It placed a cluster of one primary satellite and three smaller sub-satellites (that trailed along at distances of several hundred kilometers) into low polar orbit. This satellite array determined the location of radio and radars transmitters, using triangulation, and the identity of naval units, by analysis of the operating frequencies and transmission patterns.

In external appearance, the sub-satellites were reminiscent of the Navy's Transit navigational satellites. The had gravity gradient orientation booms 10-15 meters long. These ensured that the side of the satellite body where the signal antennas were mounted was constantly oriented toward the Earth. The satellites maintained an assigned position in a group at distances of 30 to 240 km one from the other by using on-board low-thrust engines. As a result of ground processing of direction-finding data on the signals from target emitters provided by a group of satellites, and also sequentially by several groups of satellites, the coordinates, direction and speed of travel were obtained.

Alternate Names

  • 21809
  • USA77

Facts in Brief

Launch Date: 1991-11-08
Launch Vehicle: Titan IV
Launch Site: Vandenberg AFB, United States

Funding Agency



  • Surveillance and Other Military

Additional Information


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