ACES finds its house in orbit

ACES lifted off on 21 April 2025 aboard a SpaceX Falcon 9 from NASA’s Kennedy Area Heart in Florida, United States, as a part of the thirty second SpaceX industrial resupply providers mission to the Worldwide Area Station. On 25 April, the Station’s Canadian robotic arm put in the payload on the Earth-facing aspect of ESA’s Columbus laboratory, the place it’s set to function for 30 months. 

Developed by ESA in collaboration with European trade led by Airbus, ACES carries the most accurate atomic timepieces ever launched into space: PHARAO, a caesium-based fountain clock developed by the French area company CNES, and the Area Hydrogen Maser constructed by Safran Timing Applied sciences in Switzerland. These clocks will work in tandem with a cutting-edge microwave and laser hyperlink system to ship time from orbit with unprecedented precision and permit ACES to ascertain a “community of clocks”, evaluating essentially the most correct clocks on Earth and in area to discover the character of time, check common relativity and assist pave the way in which for a redefinition of the second primarily based on next-generation optical clocks. 

With set up now full, the subsequent step is the primary switch-on of the system, scheduled for 28 April. This preliminary activation will set up communications with floor management, enabling telemetry – knowledge transmitted from ACES to Earth – and telecommands – directions despatched from engineers on the bottom to ACES – whereas stabilising thermal programs in preparation for clock operations. 

A six-month commissioning section will observe, throughout which engineers and scientists will calibrate the devices, check time switch hyperlinks and characterise the efficiency of the ACES clocks. ACES will join with clocks at chosen floor stations a number of occasions a day because it orbits Earth on the Worldwide Area Station. When a number of clocks are in the identical area of view for the Station, resembling two positioned in Europe, ACES can obtain a precision of 1 half in 10^-17, or about 10 quintillionths of a second, inside just some days. That is between one and two orders of magnitude higher than in the present day’s programs utilizing navigation satellites resembling GPS. Comparisons between distant clocks throughout continents, by no means instantly in comparison with this accuracy earlier than, will take a few week. 

By the tip of commissioning, the perfect working parameters for PHARAO will likely be outlined. ACES will then start its two-year science phase, with ten deliberate classes of 25 days of data-taking. After validation by the ACES science staff, outcomes will likely be shared with the worldwide scientific neighborhood, opening new frontiers in basic physics and the science of time. 

“I am so excited and proud that our extremely complicated and vastly necessary venture is now in area after a few years of onerous work. It is a main achievement for ESA and the science neighborhood, and I sit up for seeing the outcomes of the onerous work achieved by Airbus, Timetech, CNES, Safran Time Applied sciences and ESA, along with companions throughout Europe. That is ESA’s ‘jewel within the crown’ on the Worldwide Area Station.”
Simon Weinberg, ACES Challenge Scientist, ESA.

See our social media thread for photographs of the set up from the NASA livestream; increased decision photographs will likely be accessible at a later date.