USNO Report CGSIC Timing Subcommittee April 19, 2002 Lisa Nelson Time Service Department ; DSN

April 19, 2002CGSIC Timing Subcommittee Overview Mission Master Clock GPS Timing Operations –Precise Positioning Service (PPS) –Standard Positioning Service (SPS) Network Time Servers Internet and Other Time Products Precise Time and Time Interval (PTTI)

April 19, 2002CGSIC Timing Subcommittee U.S. Naval Observatory

April 19, 2002CGSIC Timing Subcommittee USNO Mission ( Determine positions and motion of celestial bodies, motions of the Earth and precise time Provide astronomical and timing data to the Navy and Department of Defense (DoD) Make data available to other government agencies and public –Astrometry Department –Astronomical Applications Department –Earth Orientation Department –Time Service Department USNO Alternate Master Clock

April 19, 2002CGSIC Timing Subcommittee USNO Master Clock Time Service Department Ensemble of –59 Cesium standards –12 Hydrogen masers Real-time realization of UTC(USNO) Clocks incorporated into International Atomic Time (TAI)

April 19, 2002CGSIC Timing Subcommittee USNO GPS Operations Precise Positioning Service (PPS) –Provide GPS with a reliable and stable reference to UTC(USNO) GPS Time Synchronization to UTC(USNO) GPS Time corrections provided daily to USAF GPS MCS Standard Positioning Service (SPS) –Common-view data backup to TWSTT used to incorporate USNO clocks for TAI computation –Time comparisons made with national and international timing centers (NIST, NPL, PTB) –Time steering of remote clock (LORAN-C)

April 19, 2002CGSIC Timing Subcommittee GPS Time Synchronization to UTC(USNO) GPS PPS Timing Receiver Computer UTC(USNO) Master Clock Computer 5MHz 1PPS U.S. Naval Observatory Secure Line GPS MCS Ground Antenna GPS Satellites

April 19, 2002CGSIC Timing Subcommittee Precise Positioning Service (PPS) UTC(USNO) - GPS Time GPS Time Stability 6.2 ns std Specification: +/ ns Modified Julian Day (MJD) Nanoseconds

April 19, 2002CGSIC Timing Subcommittee Precise Positioning Service (PPS) UTC(USNO) – {GPS’s prediction of UTC(USNO)-GPS} 1.37 ns std Modified Julian Day (MJD) Nanoseconds

April 19, 2002CGSIC Timing Subcommittee USNO Precise Positioning Service (PPS) GPS Timing Operations Current Operations –Single channel receivers, dual-frequency, schedule dependent operational receivers –12-channel receivers (all-in-view), dual-frequency, temperature stabilized antenna electronics and cables Running in parallel with current operational receivers Improved hardware stability

April 19, 2002CGSIC Timing Subcommittee USNO Standard Positioning Service (SPS) GPS Timing Operations Current Operations –Motorola Oncore receiver (8-channel, single frequency) Power level sensitivity –3S Navigation GPS/GLONASS Additional Systems – NovAtel GPS/EGNOS/WAAS Monitor UTC(USNO)-WAAS –Ashtech JPL Real Time Global Differential System

April 19, 2002CGSIC Timing Subcommittee Modified Julian Day (MJD) Nanoseconds Power Level Sensitivity of GPS Receiver A 0 dB 30 dB 20 dB 10 dB 0 dB

April 19, 2002CGSIC Timing Subcommittee Modified Julian Day (MJD) Nanoseconds Power Level Sensitivity of GPS Receiver B 0 dB 30 dB 20 dB 10 dB 0 dB

April 19, 2002CGSIC Timing Subcommittee USNO Network Time Servers Time Service Department Internet ( –26 U.S. Stratum-1 Time Servers –USNO Master Clock & GPS SPS Time References –Millisecond Time Synchronization –7 Billion Network Requests since January 1, 2002 Classified DoD Internet (SIPRnet) –2 U.S. Stratum-1 Time Servers –USNO Master Clock References Contact: Richard E. Schmidt, ; DSN

April 19, 2002CGSIC Timing Subcommittee USNO Internet and Other Time Products Time Service Department ftp server (ftp://tycho.usno.navy.mil) –9 million connections/month Time Service Web server ( –5 million connections/month RealAudio© Master Clock Voice Announcer ( –75 thousand connections/month –few seconds delay (RealAudio© ) Telephone Voice Announcer ( ; DSN ) Modem Time ( ; DSN ; N1)

April 19, 2002CGSIC Timing Subcommittee Precise Time and Time Interval (PTTI) Systems and Applications Meeting Objectives –Disseminate and coordinate PTTI information at the user level; –Review present and future PTTI requirements; –Inform Government and Industry engineers, technicians, and managers of precise time and frequency technology and its problems; and –Provide an opportunity for an active exchange of new technology associated with PTTI. Meeting Information ( –Annual: rotates between DC and California –Sponsors: USNO, NRL, NASA JPL, USCG NAVCEN, DISA, USAF –Attendees: U.S. government, military, industry and international –34th PTTI: December 3-5, 2002 in Reston, VA