Working application of TWSTT for high precision remote synchronization

Two-way satellite time transfer (TWSTT) is the primary method implemented to determine the synchronization error between the United States Naval Observatory (USNO) Alternate Master Clock (AMC) located in Colorado and the USNO Master Clock located in Washington, DC. A hydrogen maser at the AMC is controlled to the USNO Master Clock within 1 ns RMS as determined by low noise (<300 ps) TWSTT measurements. A Kalman filter utilizes the TWSTT time difference data to give real time synchronization and syntonization error estimates that are used in a linear quadratic Gaussian control design. Calibration runs using a mobile earth station monitor the long term performance of the TWSTT method. Results of a closed loop TWSTT calibration experiment are discussed. Remote time difference data obtained via TWSTT and the GPS are compared.