: 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.

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Performance of Atomic Clocks Flown on the Space Shuttle Experiment NAVEX

: From Oct. 30 to Nov. 6 1985 the first dedicated German Shuttle I Mission Dl with the Spacelab laboratory on board took place. One of the more than 70 experiments on board was the Navigation I Experiment NAVEX. A Cs- and a Rb-clock onboard were used for the generation of PN-code navigation signals. During the experiment these clocks were compared with the ground master clock by one-way and two-way methods. In this paper a survey will be given on the progress of the experiment and on first raw data, which indicate already a satisfactory operation of the used spread spectrum technique and a very accurate confirmation of the predicted relativistic clock effects.

S. Starker

Papers

The Shuttle Experiment Navex Completed on Spacelab Mission D1