J. Phys. Colloques
Volume 42, Numéro C8, Décembre 1981Troisième Symposium sur les Etalons de Fréquence et la Métrologie / Third Symposium on Frequency Standards and Metrology
|Page(s)||C8-395 - C8-413|
J. Phys. Colloques 42 (1981) C8-395-C8-413
ULTRA-ACCURATE INTERNATIONAL TIME AND FREQUENCY COMPARISON VIA AN ORBITING HYDROGEN-MASER CLOCKD.W. Allan1, C.O. Alley2, N. Ashby3, R. Decher4, R.F.C. Vessot5 et G.M.R. Winkler6
1 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.
Hydrogen maser clocks have exhibited fractional frequency stabilities of better than 1 x 10-15 for averaging times as large as 20,000 seconds . This represents an rms time deviation of about 20 ps for ¼ day prediction times . 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 . 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.