Photo credit: www.esa.int
The Atomic Clock Ensemble in Space (ACES), a cutting-edge timekeeping instrument from the European Space Agency (ESA), has officially been installed on the Columbus laboratory aboard the International Space Station (ISS). A recent image captured by cameras outside the Station showcases ACES in its new setting. For the past 25 years, these cameras have provided unique, real-time perspectives of activities in orbit, documenting significant events like this installation.
On April 25, the Canadian Space Agency’s robotic arm meticulously removed ACES from the SpaceX Dragon spacecraft’s trunk and positioned it on the Columbus External Payload Facility, adjacent to ESA’s Atmospheric-Space Interactions Monitor (ASIM). Installed on the side facing Earth, ACES will synchronize with terrestrial clocks as the ISS completes its orbit around our planet approximately sixteen times daily.
Developed by ESA, with leadership from European industry giants including Airbus, ACES carries what are considered the most accurate clocks ever deployed in space: the PHARAO clock, crafted by the French space agency CNES, and the Space Hydrogen Maser created by Safran Timing Technologies of Switzerland. These instruments, working in conjunction with advanced microwave and laser systems, will enable unprecedented comparisons of time between space and Earth, facilitating tests of fundamental physics and laying the groundwork for future timekeeping standards.
ACES arrived at NASA’s Kennedy Space Center in March 2025, where collaborative teams from ESA, Airbus, and NASA prepared the payload for its mission. The payload was successfully launched on April 21 aboard a SpaceX Falcon 9, as part of the 32nd commercial resupply mission to the ISS. Recently, ACES was powered on for the first time, establishing communication with ground control and calibrating its thermal systems to begin clock operations.
A commissioning phase lasting six months is now set to commence, after which ACES will initiate its two-year science mission. This endeavor aims to push the boundaries of fundamental physics and timekeeping science.
Source
www.esa.int