Dissemination of time and frequency by satellite

A description is given of the three different modes of satellite time and frequency transfer. One method uses geostationary satellites to distribute time signals of the U.S. National Bureau of Standards to a large number of users. This method could eventually replace some of the existing radio time and frequency broadcasts. A second method uses navigation satellites carrying time standards. Such satellites are important sources of accurate time dissemination. The third method employs two-way repeaters on communications satellites. This method has been used extensively by the U.S. Naval Observatory. Its main use is restricted to linking distant time stations because ground stations are very expensive and in fixed locations.