ACES vacuum testing

The Atomic Clock Ensemble in Space (ACES) is a European facility that will test fundamental physics from the outside of ESA’s Columbus module on the International Space Station. By creating a “network of clocks”, ACES 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, a caesium atomic clock developed by the French space agency CNES and the Space Hydrogen Maser, a clock which uses hydrogen atoms, produced by Safran Time Technologies. 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. 

ACES is fully assembled at Airbus in Friedrichshafen, Germany, where it is undergoing rigorous testing, such as the vacuum testing seen in this image, 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.