Most accurate space clock set to launch – and count down to destruction

The countdown to the launch of the most accurate clock in space has begun, with the Atomic Clock Ensemble in Space (ACES) set to revolutionize timekeeping both in orbit and on Earth. This European Space Agency (ESA) mission will deploy a network of highly precise clocks that will transmit synchronized time signals to ground stations as the International Space Station orbits the planet at 27,000 kilometers per hour.

Expected to launch on 21 April aboard a SpaceX Falcon 9 rocket from Kennedy Space Center, Florida, ACES will be attached to the exterior of ESA’s Columbus laboratory on the ISS using the Canadarm2 robotic arm. The mission aims to test Einstein’s theory of general relativity and advance research in various scientific fields, from dark matter to string theory.

The heart of ACES lies in its two clocks: SHM, designed for short-term stability to calibrate the primary clock, PHARAO. Together, these clocks boast unparalleled accuracy, losing less than one second over 300 million years. PHARAO, a marvel of miniaturization, operates by cooling cesium atoms to near absolute zero and observing their behavior in microgravity to generate precise time signals.

Simon Weinberg, an ESA representative, emphasized the sensitivity and precision of PHARAO, highlighting the challenges of measuring time at such minute intervals. Once operational, ACES will spend a year and a half commissioning and fine-tuning its clocks to eliminate any noise and ensure optimal performance.

Despite its groundbreaking capabilities, ACES has a limited operational lifespan, scheduled to operate until 2030 when the ISS is expected to deorbit. However, plans for a new generation of space clocks are already in the works, ensuring that the legacy of precise timekeeping in space continues beyond the current mission.

As technology evolves, optical clocks may eventually replace atomic clocks, offering even greater accuracy and reliability. But for now, ACES stands as a beacon of innovation and scientific advancement in the realm of space-based timekeeping.