The transit system, 1975

This report describes the development and 1975 status of the Transit System (Navy Navigation Satellite System). Transit has been available for military use since 1963 and for public use since 1967, providing all-weather navigation to world-wide users. For users on land, the system provides a standard for global surveying data. A single 15-min data span provides the necessary data for an on-land user to obtain his position with a 20- to 40-m precision. If all the data available in a 2-day period are used, then the position is good to a 1- to 5-m precision. The position is specified in a global datum system and is free of the limitations associated with local datum coordinates. At the time of this writing, five satellites were in polar orbits. The system has been continuously updated and improved with no user changes required. In late 1975, the geopotential model used for the previous 7 years was replaced by the DoD model WGS-72. The importance of the change to system users is discussed.