Telstar Time Synchronization

A broad-band completely reciprocal transmission path across the Atlantic was made available for the first time by the Telstar I satellite. In August, 1962, the U. S. Naval Observatory (USNO) and the National Physical Laboratory (NPL) cooperated in an experiment using the satellite to relate the master clocks at the USNO, and the Royal Greenwich Observatory (RGO) at Herstmonceux, U. K. Pulsed signals, 5 μs long, at the rate of ten per second were transmitted simultaneously over the satellite circuit from the ground stations at Andover, Me. and Goonhilly Downs, Cornwall, U. K. The time difference between received and transmitted pulses was measured at each station and from these results the relative setting of the station clocks was obtained directly. In the final experiment on August 27th, the Goonhilly clock was found to be 72.6±0.8 μs ahead of Andover. The internal consistency of the results was checked by comparing the measured time delays of the signals over whole or part of the path with the value calculated from the satellite ephemeris, based entirely on Minitrack observations. The measured time delays were consistent to ±1 μs and did not differ from the ephemeris by more than 6 μs, equivalent to 1 km error in range. The time synchronization between the ground stations was extended to the observatory clocks by low-frequency ground-wave signals propagating with known velocities.