The space clock PHARAO: functioning and expected performances

The cold atom space clock PHARAO is one of the ultra-stable atomic clocks of the ESA supported ACES mission. ACES will fly on an external pallet of the European module Columbus of the International space station between mid 2006 and the end of 2007. The goal of PHARAO is the study and utilization of a laser cooled cesium clock in microgravity environment. The French space agency, CNES, is funding and managing the clock construction with the support of the BNM-SYRTE and LKB laboratories for the clock requirements and follow-up of subsystem development in industrial companies. The clock sub-systems have been designed and the engineering models will be delivered in 2003 to the CNES technical center, in Toulouse, where the clock will be assembled, tested and evaluated. In this paper, we present the PHARAO performances in term of frequency stability and accuracy and the technical solutions developed to reach these performances.