On Monday 21 April, the European Space Agency’s (ESA) Atomic Clock Ensemble in Space (ACES) lifted off from Florida (USA) aboard a SpaceX Falcon 9 rocket, as part of the 32nd SpaceX commercial resupply mission to the International Space Station.
ACES, with two cutting-edge clocks - the Space Clock with Cold Cesium Atoms (PHARAO) and the Space Hydrogen Maser (SHM) - and an advanced time transfer system, should provide the most accurate time signal ever transmitted from space and connect the world’s best clocks to test fundamental physics from orbit, including Einstein’s theory of relativity, according to ESA. By creating a “network of clocks”, ACES will link its own high-precision clocks to the most accurate clocks on Earth and compare them to measure the passage of time.
The clocks will generate a time signal so precise that ACES would lose just one second in 300 million years. The time transfer system will use microwave and laser links to synchronise time between space and Earth with far greater precision than current systems.
On 25 April, the International Space Station’s robotic arm will install ACES on the External Payload Facility of ESA’s Columbus module, facing Earth. Over the course of its 30-month mission, ACES aims to conduct at least ten extended measurement sessions, each lasting 25 days, as it orbits Earth 16 times daily. (Original version in French by Camille-Cerise Gessant)