The spatial clock redefines the time measurement itself

Time varies in space – the revolutionary European timepiece launched this week will prove this with unprecedented precision.

The Atomic Clock Ensemble in Space (ACE) successfully reached orbit on April 21, launching the SpaceX Falcon 9 rocket from NASA’s Kennedy Space Center. The mission is the most accurate timing system ever, and on the International Space Station, it will test basic physics theories while losing only one second every 300 million years.

“The launch of ACES marks a major milestone in European scientific and international space cooperation,” said Daniel Neuenschwander, director of human and robot exploration at ESA. “With this mission, we deliver the most accurate clocks ever to the International Space Station orbit – opening up new boundaries for fundamental physics, time shifts and global synchronization.”

At the heart of Aces are two compelling clocks: the pharao (Projet d’Horloge Atomiqueà Redom of the atomic eN Orbite) and SHM (Space Hydrogen Maser), developed by the French Space Agency CNES, built by Safran Time Intering Technology in Switzerland.

The Pharao clock uses laser to cool the cesium atoms to almost absolute zero (about -273 degrees Celsius), allowing incredibly accurate time measurements. Unlike the skull clock that requires significant heights to run heights, the French use the station’s microgravity environment to achieve the same accuracy in smaller packages – approximately the same size as the compact refrigerator.

Meanwhile, the SHM clock uses hydrogen atoms as its frequency reference, similar to the technology used in the European Galileo navigation satellite, but with higher stability. These tools will sustain time with amazing accuracy—the equivalent of losing only one second in 300 million years.

The scientific implications go far beyond simple timing. ACE will directly test Einstein’s general theory of relativity, which predicts gravity will affect the passage of time. Previous Earth-based experiments have confirmed that at higher altitudes with weaker gravity, the clock runs slightly higher. ACE takes this verification to new heights by comparing its space clock with the world’s most advanced ground clocks.

“We are excited about the opportunities that ACES has built for basic physics research, geographic applications and global timing work,” said Luigi Cacciapuoti, ACES project scientist at ESA. “Aces are now dealing with the urgent need in the scientific community and will certainly play a key role in promoting the redefinition of standard time units – in terms of optical frequency standards, the so-called SI second.”

The launch path is not simple. The sensitivity to engineering the equipment, which can measure time with such extraordinary precision – but powerful enough to survive the rigor of launch and space operations – presents a huge challenge to the project’s three decades of development.

“ACES is a highly sensitive device made of complex and interconnected subsystems that must work in harmony,” explained Thomas Peignier, principal engineer at ACES. “The team faced many challenges and had to design clever solutions. For example, to prevent the clock from being damaged by contact with the magnetic field, we conducted a magnetic survey and then moved the ACE anywhere, using special equipment, protecting the ACE during the test, as well as all tools, electronics and metal parts, and measurements with nuts and bolts, and when necessary, and measurements were made nearby.

Later this week, the robot arm will install the ACE outside the ESA’s Columbus module, located in a position facing the earth. The facility will operate for 30 months, orbiting the Earth 16 times a day, collecting data through at least ten measurement sessions.

The task connects clocks across continents through microwave and laser links that synchronize time between space and Earth with unprecedented accuracy. Ground stations throughout Europe, the United Kingdom, the United States and Japan will communicate with ACES to compensate for the severe conditions of atmospheric impact and space.

In addition to testing relativity, ACE will also look for changes in the basic physical constants and may detect evidence of dark matter. It will also enable scientists to measure the differences in the gravity fields of Earth across continents and synchronize with current satellite systems that cannot improve global time to impossible levels.

With Aces Orbits 400 kilometers above Earth, it drives human understanding of time itself – potentially changing our definition of the most basic unit of measurement while demonstrating Europe’s leadership in cutting-edge space science.