The U.S. Naval Observatory has maintained a Time Service Department since 1880. At right are a pair of Reifler precision pendulum clocks, photographed in their underground vault c. 1910. Today, USNO's Precise Time Department is charged with maintaining the DoD reference for Precise Time and Time Interval (PTTI). That reference is UTC(USNO). This time-scale is determined by an ensemble of dozens of atomic frequency standards, popularly called "atomic clocks", which are continuously scanned, selected, and averaged by computer to provide a day-to-day precision measured at the picosecond (10-12 seconds) level per day.
USNO Master Clock
The DoD common time reference is the U.S. Naval Observatory Master Clock. It is generated at USNO in Washington, D.C. and at the
Alternate Master Clock Facility at Schriever Space Force Base in Colorado.
GPS
USNO monitors the Global Positioning System (GPS) constellation and provides system timing offsets to the U.S. Space Force 2nd Space Operations Squadron (2SOPS), timing data for individual GPSsatellites, and time transfer services using GPS.
NETWORK TIME SYNCHRONIZATION
USNO providesauthoritativenetwork time synchronizationvia the Network Time Protocol (NTP).
Two-way satellite time transfer (TWSTT)
The highest precision and accuracy in time dissemination is provided through Two-Way Satellite TimeTransfer(TWSTT). USNO provides operational time transfer and calibration services for TWSTT.
Telephone Time
USNO provides both voice announcements of the time, and services to synchronize systems over telephone modems.
Research
USNO is in the forefront ofdeveloping robust, continuously running atomic frequency standards. Our Clock Development Divisionhas designed, built, and deployed six
rubidium fountain clockswhich have been operating continuously since 2013. The team is now investigating optical frequency standards, which will operate at frequencies some five orders of magnitude higher than the current microwave standards.
