Performance and Results of Portable Clocks in Aircraft

Abstract : During the first two weeks of October, 1971, Richard E. Keating of the U.S. Naval Observatory and I flew twice around the world on regularly scheduled commercial flights, once eastward and once westward, with four Hewlett-Packard 5061A cesium beam clocks. For about a week before the first trip, between the trips, and for about a week after the second trip, we recorded a continuous phase comparison between each clock and the MEAN (USNO) time scale. Time differences among the four clocks also were recorded with a time interval counter at regular intervals before, during, and after each trip, thereby permitting evaluation of the flying mean time scale. The experiment was conducted for two reasons: (1) to compare the known performance of similar clocks under fairly well-controlled laboratory conditions, and (2) to try to detect relativistic effects on the time recorded by clocks during terrestrial circumnavigations. It was performed with the interest and complete cooperation of Dr. G. M. R. Winkler and others of the Naval Observatory Time Service Division, and with financial support from the Office of Naval Research. A major portion of the credit for the experiment goes to Richard Keating, whose steadfast desire to perform such an experiment generated the necessary motivation. Although the performance of these clocks was found to be noticeably degraded during the trips, we also found that the ensemble of four flying clocks produces consistent time differences which are difficult to explain without invoking relativistic effects.