In a historic leap for precision science, the European Space Agency (ESA) has installed the world’s most advanced atomic clock system on the International Space Station (ISS).
Known as the Atomic Clock Insemble in Space (ACES), this groundbreaking facility was launched on April 21, 2025, on aboard a SpaceX Falcon 9 rocket.
On April 25th, the Canadian robotic arm is mounted on an ACE carefully placed on the Earth plane of ESA’s Columbus Institute.
ACES is set to run for 30 months and will put together the most accurate atomic clocks ever sent into space.
ACES is designed to help maintain time with unprecedented accuracy, push the boundaries of fundamental physics, transform global timekeeping, and redefine how humanity measures time itself.
What is an atomic clock?
Atomic clocks are highly accurate timekeeping devices based on oscillations of atoms, usually cesium or hydrogen vibrations.
Unlike traditional clocks that rely on mechanical components and quartz vibrations, atomic clocks take advantage of the consistent frequency of atomic transitions.
This allows you to maintain incredible accuracy. This can be lost or gained seconds over millions of years.
Atomic clocks are important for GPS systems testing laws of physics, deep space navigation, communications, and scientific experiments.
The science behind the ace
Developed by Airbus in Europe’s industry leadership, ACES features two groundbreaking watches: Pharaoh, a cesium fountain watch developed by French CNES, and Space Hydrogen Maser, Swiss Saffron Timing Technology.
These instruments combine with sophisticated microwaves and laser links to allow for the transfer of time from space with unparalleled accuracy.
By connecting the Earth and the clock in orbit, the ACE can create a network of clocks, allowing scientists to explore the nature of time itself, test predictions from Einstein’s general theory of relativity, and lay the foundation for redefine the second with the next generation of optical clocks.
Simon Weinberg, ACES Project Scientist at ESA, added:
“This is a huge achievement for the ESA and the scientific community. We look forward to seeing the results of the hard work that Airbus, Timetech, CNES, Saffron Time Technology and ESA have done with partners across Europe. This is the “jewel” of the International Space Station ESA. ”
The road ahead
After installation, the first activation of ACES is set to today (April 28, 2025). The engineer establishes a communications link with the terrestrial station, stabilizes the thermal system and prepares the system to fully operate.
Over the next six months, we will adjust the equipment during the rigorous commissioning phase to test the system’s exceptional time travel capabilities.
ACES is expected to achieve time comparison accuracy within a second, 10 to 100 times better than current GPS-based systems.
Once commissioning is over, ACE enters a two-year science phase, providing new insights into fundamental physics, revolutionizing the science of time measurement.
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