Simulation of servo loops in Atomic Clock Ensemble in Space (ACES)

Atomic Clock Ensemble in Space (ACES) is an ESA mission that will operate a new generation of atomic clocks in micro-gravity environment of the International Space Station (ISS). Two high performance atomic clocks in ACES: the Space Hydrogen Maser (SHM) and PHARAO, a clock based on laser cooled cesium atoms, are compared on-board the ISS and locked together by two separate servo-loops: short and long term servo loop. This paper presents a simulation model for the complete system that evaluates the performance of the ACES clock signal at its output using frequency domain techniques. The results of ACES servo loop simulations for both PHARAO ground and space models are presented. Result for PHARAO ground model is compared to ACES system level test that has been performed in Toulouse, 2009.