Time and frequency activities at the U.S. Naval Observatory

Demetrios Matsakis

doi:10.1109/ursigass.2011.6050335

Abstract

The U.S. Naval Observatory (USNO) has provided timing for the Navy since 1830 and, via DoD Directive 4650.05, is the sole source of timing for the Department of Defense. In cooperation with other institutions, the USNO also provides timing for the United States and the international community. Its Master Clock (MC) is the source of UTC (USNO), USNO's realization of Coordinated Universal Time (UTC), which has stayed within 5 ns rms of UTC since 1999 and within 4 ns rms in 2010. The data used to generate UTC (USNO) are based upon 69 cesium and 26 hydrogen maser frequency standards in four buildings at two sites. USNO disseminates time via voice, telephone modem, Network Time Protocol (NTP), GPS, and Two-Way Satellite Time Transfer (TWSTT). To meet space limitations, this document will describe only the timescale algorithm and GPS time transfer precision. Further details and explanations of our services can be found online at http://www.usno.navy.mil/usno.

Highlights

The determination of time has been a crucial factor in navigation for centuries
With the advent of radio navigation, the need for precise time was pushed to the nanosecond level because the light travel time, when converted to distance at the approximate rate of passing 1 meter in 3 nanoseconds, was used for triangulation
In order to serve navigational needs of GPS, as well were time and frequency requirements of other users and systems, the US Naval Observatory (USNO) has specialized in real-time, robust timekeeping

Summary

INTRODUCTION

The determination of time has been a crucial factor in navigation for centuries. With the advent of radio navigation, the need for precise time was pushed to the nanosecond level because the light travel time, when converted to distance at the approximate rate of passing 1 meter in 3 nanoseconds, was used for triangulation. This determination requires knowledge or inference of the relevant clocks’ times to this level. In order to serve navigational needs of GPS, as well were time and frequency requirements of other users and systems, the USNO has specialized in real-time, robust timekeeping. This paper describes how time is generated at the USNO and transferred to the users

TIME GENERATION

TIME TRANSFER

MEASURES TO SECURE THE ROBUSTNESS OF THE MASTER CLOCK

Findings

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