Performance of Atomic Clocks Flown on the Space Shuttle Experiment NAVEX

At the first German Spacelab Mission D1 in autumn 1985 a navigation experiment was flown for seven days on board the NASA Space Shuttle Challenger. Two atomic clocks, one Cs- and one Rb-standard, were part of the spaceborne equipment and were carried back to earth. The Cs-clock was compared with a ground based Cs-clock by a two way microwave link at 1.5 GHz in the periods of ground contact, while the comparison between the flying Cs- and Rb-clock occurred continuously. The influence of the space flight on clock rates was determined by comparison with many series of measurements on the ground before and after the D-1 Mission. Comparisons of the flight clocks at Cape Kennedy with the reference clock in Germany were performed via GPS. Results of the data evaluation will be presented with special attention to temperature effects. Unexpected rate oscillations between the two flying clocks correlated with the attitude of the space vehicle were discovered.