ACES ground segment functionality and preliminary operational concept

Atomic Clock Ensemble in Space (ACES) is a mission of the European Space Agency (ESA) based on a new generation of atomic clocks: a Cesium clock (PHARAO) based on laser-cooled atoms and an active Space Hydrogen Maser (SHM). The ACES clock signal will reach frequency stability and accuracy at the 10^-16 level. Disseminated to ground via a dedicated link in the microwave domain, the ACES time scale will be used to perform comparisons with high-performance ground clocks. The payload will be operated in the microgravity environment of the International Space Station (ISS) and it is planned to be launched in 2013. The ACES Ground Segment (GS) will be integrated within the overall ISS ground architecture providing the communication links between ground and space through the Columbus Control Centre and NASA ground segment. ACES GS consists of two main components: the Users Support and Operations Centre (USOC) and a network of remotely controlled Micro-Wave-Link Ground Terminals (MWL GTs) distributed worldwide. The MWL GTs will interface with the ground clocks located at the laboratories and research institutes participating in ACES. This paper presents the baseline architecture of ACES ground segment, its main functionalities and the preliminary operational concept. ACES GS preliminary design review is planned for summer 2009.