ACES/PHARAO space program status

The atomic clocks ensemble in space (ACES) is a European Space Agency mission dedicated to fundamental metrology based on distant clocks comparisons. The payload will be accommodated on-board the International Space Station (ISS). It is made up two clocks, a two way time transfer link and a GPS-GALILEO receiver. A new type of atomic clock using laser cooled atoms, Pharao, will be operated with 10^-16 relative frequency stability and accuracy. This clock is developed by CNES, the French space agency. The second clock is an H-maser developed in Switzerland to keep time for duration less than 10000s. The time transfer device, developed in Germany, can compare on board clock with earth based clocks with a time resolution of 0:3 ps at 300 seconds, 7 ps per day and 23 ps at 10 days. Finally the GALILEO/GPS receiver will provide the data needed to reconstruct the ISS orbit and, in turn, position and velocity of the ACES clocks. In this paper, we review the first performances ground tests carried out on each engineering model ACES instrument.