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ABOUT US
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Naval Oceanography One Pager
End of Year Graphic 2022
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The USNO Master Clock
The USNO Master Clock
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USNO Alternate Master Clock (AMC)
Cesium Atomic Clocks
Hydrogen Masers at the USNO
Rubidium Fountain Clocks
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International Time Scales and the BIPM
Definitions of Systems of Time
Global Positioning System
Global Positioning System Overview
USNO GPS Data Categories Explanation
CGGTTS Data Format
USNO GPS Time Transfer
Leap Seconds
GPS Information: SA, DGPS, Leap Seconds, etc.
GPS Week Number Rollover
GPS Timing Data and Information
USNO Format Explanation
USNO Computer Display Clocks
Two-Way Satellite Time Transfer (TWSTT)
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United States Naval Observatory
Precise Time Department
Two-Way Satellite Time Transfer (TWSTT)
Home
Our Commands
United States Naval Observatory
Precise Time Department
Two-Way Satellite Time Transfer (TWSTT)
ABOUT US
Mission & Vision
History
Naval Oceanography One Pager
End of Year Graphic 2022
LEADERSHIP
Commander
Technical Director
Command Master Chief
All Leadership
OUR COMMANDS
Naval Oceanographic Office
Fleet Numerical Meteorology & Oceanography Center
United States Naval Observatory
News from the Naval Observatory
Earth Orientation Department
Precise Time Department
The USNO Master Clock
The USNO Master Clock
Time Dissemination at the USNO
USNO Alternate Master Clock (AMC)
Cesium Atomic Clocks
Hydrogen Masers at the USNO
Rubidium Fountain Clocks
USNO Time Scales
International Time Scales and the BIPM
Definitions of Systems of Time
Global Positioning System
Global Positioning System Overview
USNO GPS Data Categories Explanation
CGGTTS Data Format
USNO GPS Time Transfer
Leap Seconds
GPS Information: SA, DGPS, Leap Seconds, etc.
GPS Week Number Rollover
GPS Timing Data and Information
USNO Format Explanation
USNO Computer Display Clocks
Two-Way Satellite Time Transfer (TWSTT)
Telephone Time
Network Time Protocol (NTP)
US Eastern Time Zone NTP Servers
US Mountain Time Zone Servers
DoD Customer Servers
Astronomical Applications Department
Celestial Reference Frame Department
Senior Enlisted Advisor
Careers at the USNO
Naval Oceanography Operations Command
Fleet Weather Center - Norfolk
National Ice Center
Fleet Weather Center - San Diego
Joint Typhoon Warning Center
Naval Oceanography Anti-Submarine Warfare Center
Navy DoD Supercomputing Resource Center
PRESS ROOM
News Stories
Photo Gallery
Video Gallery
Public Use of Limitations
CAREERS AND INTERNSHIPS
CONTACT US
Two-way Satellite Time Transfer
Overview
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).
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