ACES status at completion of the engineering models phase

Atomic Clock Ensemble in Space (ACES) is a pioneering mission that will use high performance atomic clocks to test fundamental laws of physics. Operated in the microgravity environment of the International Space Station, the ACES clocks, PHARAO and SHM, will generate a frequency reference reaching instability and inaccuracy at the 1·10^-16 level. A high-performance link in the microwave domain (MWL) will distribute on ground the ACES signal allowing for comparisons of distant clocks to a frequency resolution of 1·10^-17. ACES will connect ground clocks based on different atoms and atomic transitions in a worldwide network that will probe fundamental laws of physics to high accuracy. Space-to-ground and ground-to-ground comparisons of atomic frequency standards will be used to test Einstein´s theory of general relativity including a precision measurement of the gravitational red-shift, a search for time variations of fundamental constants, and tests of special relativity. Applications in geodesy, GNSS remote sensing, optical time transfer, and ranging (via the ELT optical link) will also be supported. ACES has presently reached an advanced status of development, with engineering models of key instruments and subsystems completed and tested. The ACES Payload Critical Design Review and the Ground Segment Preliminary Design Review were recently completed. The ACES engineering model workbench has been integrated and characterized in a test campaign recently conducted at CNES facilities in Toulouse. The first prototype of the ACES MWL ground terminal is being assembled ready for delivery. The ACES ground segment architecture has been defined. Based on an extension of the standard Columbus USOC (User Support and Operations Center) located in CADMOS - Toulouse, the ACES USOC will remotely control the network of MWL ground terminals, and it will provide the necessary interface with the Columbus Control Center and the ACES user community.- The current development status of the ACES mission elements will be presented and discussed. An overview of future planning will be given.