Two-way Satellite Time Transfer
The U.S. Naval Observatory maintains precise time and the nation's Master Clock with the goal of providing the most precise time to remote users. The U.S. Naval Observatory has been developing the two-way satellite time transfer method since the first communications satellites, i.e. Telstar and Relay-II, were put into operation in the very early 1960's. The development of low-cost, portable, very small aperture terminals (VSATs) allowed the two-way time transfer method to be put into regular use at the U.S. Naval Observatory.
Distributing the Master Clock
The goals of the two-way project have been to improve the USNO Master Clock (USNO(MC)), its operational utility to military and civilian remote users, and to improve time comparisons with other timing laboratories and operational users both inside and outside the DoD.
The USNO(MC) is improved because two-way transfer allows inclusion into USNO's operational time scale remote clocks via the most precise and accurate timing links possible.
The operational utility to military users is increased because high precision military users are able to make direct comparisons of remote clocks with the USNO(MC) via independent means from other military operational timing systems such as the Global Positioning System (GPS). The two-way timing links with national timing laboratories will improve the short-term stability of the International Atomic Time (TAI), and with it Coordinated Universal Time (UTC).