Two-Way Time Transfer via Geostationary Satellites NRC/NBS, NRC/USNO and NBS/USNO via Hermes and NCR/LPTF

C.C. Costain, J.S. Boulanger, H. Daams, D.W. Hanson, R.E. Beehler, A.J. Clements, D.D. Davis, W.J. Klepczynski, L. Veenstra, J. Kaiser, B. Guinot, J. Azoubib, P. Parcelier, G. Freon, M. Brunet

Abstract:	The two-way time transfer using the Hermes (CTS) satellite and the Symphonie satellite began in July, 1978. The Hermes experiment finished at the end of June 1979, and the Symphonie experiment will continue until the end of 1980. The N.R.C. uses terminals at the Communication Research Center about 25 miles from the N.R.C. laboratory, and the time transfer from N.R.C. to C.R.C. is made using line of sight TV reception with frequent checks by portable cesium or rubidium clocks. Initially the USNO used Goddard terminals, and the NBS a HEW terminal in Denver, and both relied primarily on portable clock synchronization. For the last eight months, Comsat terminals were used at the USNO and at NBS, so that no secondary time transfer was required. In France, the PBS Symphonie terminal is in Brittany, 300 miles from the Laboratoire de Temps et fréquence (LPTF) at the Observatoire de Paris, and the time transfer to the terminal is made via the TV networks. The uncertainty in this latter link is about 20 ns, but for the other stations the uncertainty is 1 to 5 ns. In most of the experiments, 1 pps pulses of the station atomic clocks were exchanged between the partners, and a cubic equation was fitted to the 1000 to 2000 second measurements. The equations were exchanged and substracted to obtain the time difference of the stations. The standard deviation in the fit of the equations varied, depending on conditions, from 1.5 ns to 16 ns. For the last month of the Hermes experiment a 1 MHz signal was used, giving a standard deviation of 0.18 ns. The comparison of the time scales via satellite and via Loran-C (BIH Circular D) show clearly that some Loran-C links are very good, but that the NBS link varies by 1 us. Via the satellite the frequencies of the time scales can be compared with an accuracy of 2 x 10-14.
Published in:	Proceedings of the 11th Annual Precise Time and Time Interval Systems and Applications Meeting November 27 - 29, 1979 Goddard Space Flight Center Greenbelt, Maryland
Pages:	499 - 519
Cite this article:	Costain, C.C., Boulanger, J.S., Daams, H., Hanson, D.W., Beehler, R.E., Clements, A.J., Davis, D.D., Klepczynski, W.J., Veenstra, L., Kaiser, J., Guinot, B., Azoubib, J., Parcelier, P., Freon, G., Brunet, M., "Two-Way Time Transfer via Geostationary Satellites NRC/NBS, NRC/USNO and NBS/USNO via Hermes and NCR/LPTF," Proceedings of the 11th Annual Precise Time and Time Interval Systems and Applications Meeting, Greenbelt, Maryland, November 1979, pp. 499-519.
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