Troisième Symposium sur les Etalons de Fréquence et la Métrologie / Third Symposium on Frequency Standards and Metrology

J. Phys. Colloques 42 (1981) C8-395-C8-413
DOI: 10.1051/jphyscol:1981846

ULTRA-ACCURATE INTERNATIONAL TIME AND FREQUENCY COMPARISON VIA AN ORBITING HYDROGEN-MASER CLOCK

D.W. Allan¹, C.O. Alley², N. Ashby³, R. Decher⁴, R.F.C. Vessot⁵ et G.M.R. Winkler<sup>6

1</sup>  National Bureau of Standards, Boulder, Colorado, U.S.A.
²  University of Maryland, College Park, Maryland, U.S.A.
³  University of Colorado, Boulder, Colorado, U.S.A.
⁴  Marshall Space Flight Center, Huntsville, Alabama, U.S.A.
⁵  Smithsonian Astraphysical Observatory, Cambridge, Massachusetts, U.S.A.
⁶  U.S. Naval Observatory, Washington, DC, U.S.A.

Abstract
Hydrogen maser clocks have exhibited fractional frequency stabilities of better than 1 x 10^-15 for averaging times as large as 20,000 seconds [1]. This represents an rms time deviation of about 20 ps for ¼ day prediction times [2]. S-band Doppler cancellation frequency comparison techniques have been developed with phase stabilities of a few picoseconds [2,3]. Laser ranging systems have been developed with accuracies of a few cm [4]. Combining the virtues of these developments and choosing a satellite with an appropriate orbit would allow worldwide time comparisons at the subnanosecond level, and frequency comparison uncertainties of the order of 1 x 10^-16. Such a capability would open up new horizons to the frequency standards laboratories, to the VLBI community, to the Deep Space Tracking Network, and to fundamental time and frequency (T/F) metrology on a worldwide basis, as well as greatly assisting the BIH in the generation of UTC and TAI.