Test of a space cold atom clock prototype in the absence of gravity

We describe a space cold atom clock prototype and its operation on board an aircraft. We have recorded the atomic resonance in zero gravity during par abolic flights. This experiment must be considered as an essential step tow ard the construction of a space clock using cold atoms. In a microgravity e nvironment, a cold atomic clock would outperform all groundbased clocks. By the year 2002, we plan to operate a cold atom clock on board the internati onal spate station. This mission is called atomic Clock Ensemble in Space ( ACES), We hare also performed a preliminary accuracy evaluation of the prot otype, The interrogation of the cold atoms is performed inside a TE013 cavi ty. On earth, the phase, variations of the held induce a relative frequency shift of about 1 x 10(-13). Although the frequency shift is expected to st rongly decrease in microgravity, this cavity does not seem suitable for a 1 x 10(-16) frequency uncertainty.