ACES on Columbus

The Atomic Clock Ensemble in Space (ACES) facility attached to the exterior of ESA's Columbus facility on the International Space Station. By creating a "network of clocks", this European facility will link its own highly precise timepieces with the most accurate clocks on Earth and compare them to measure the flow of time.

ACES includes two cutting-edge clocks: PHARAO and SHM (Space Hydrogen Maser). The excellent stability of SHM over a one hour period combined with the long-term stability and accuracy of PHARAO provide timekeeping for ACES with a precision of one second over 300 million years.

Once in space, a robotic arm will position ACES onto the Columbus module, where it will remain for 30 months to collect data. ACES aims to record continuous data over at least ten sessions of 25 days each. The experiment will be operated from Europe, through CADMOS in Toulouse, France, and the Columbus Control Centre near Munich, Germany. 

The ACES science is truly interdisciplinary. By comparing clocks in space and on Earth, ACES will provide scientists with precise measurements to test Einstein’s gravitational time dilation effect, search for time variations of fundamental constants of physics and hunt for dark matter.  

ACES is fully assembled at Airbus in Friedrichshafen, Germany, where it is undergoing rigorous testing until the end of the year, after which it will be ready for its launch on a SpaceX Falcon 9 rocket, which is expected to take place in the first half of 2025.