NRL was also responsible for developing the Vanguard rocket launch vehicles through a contract to the Martin Company (which had built the Viking rockets), developing and installing the satellite tracking system, and designing, constructing, and testing the satellites. The tracking system was called Minitrack. The Minitrack stations, designed by NRL but subcontracted to the Army Corps of Engineers, were 14 stations along a north–south line running along the east coast of North America and the west coast of South America. Minitrack was the forerunner of another NRL-developed system called NAVSPASUR, which remains operational today under the control of the Air Force and is a major producer of spacecraft tracking data.