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

Highly Accurate Atomic Clock Set for Launch to the International Space Station

The most precise atomic clock ever designed for space is poised to launch within days, initiating the development of an exceptionally synchronized network utilizing Earth’s most sophisticated timekeeping instruments. This project, decades in the making, is slated for a brief operational period before its eventual descent as the International Space Station (ISS) deorbits by the decade’s end.

ACES Mission: Redefining Time Measurement in Space

The Atomic Clock Ensemble in Space (ACES), a key undertaking by the European Space Agency (ESA), is engineered to produce a time signal with unmatched accuracy. Orbiting at speeds of 27,000 kilometers per hour, ACES will transmit this highly precise signal via laser to nine ground-based stations. This network of synchronized clocks will establish a global standard for highly accurate timekeeping.

Testing Einstein’s Theory and Advancing Scientific Research

Consequently, ACES will offer an unprecedented opportunity to rigorously test Einstein’s theory of general relativity. This theory posits that the passage of time is influenced by gravitational forces. The mission’s high precision will also aid in diverse scientific inquiries, spanning from investigations into dark matter to advancements in string theory.

Launch and Deployment Details

ACES is scheduled to commence its journey on April 21, launching aboard a SpaceX Falcon 9 rocket from Kennedy Space Center in Florida. Upon reaching the ISS, Canadarm2, the robotic arm provided by the Canadian Space Agency, will carefully attach ACES to the exterior of ESA’s Columbus laboratory, positioning it in the vacuum of space for its operations.

Dual Clock System for Enhanced Precision

The ACES payload incorporates two distinct clocks: SHM and PHARAO. The Short-Term Stability Hydrogen Maser (SHM) is designed for exceptional short-term stability, crucial for calibrating PHARAO (Projet d’Horloge Atomique par Refroidissement d’Atomes en Orbite). Together, these clocks are engineered to achieve remarkable accuracy, potentially losing less than one second over a staggering 300 million years – representing a tenfold improvement over the precision of clocks currently used in GPS satellites.

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Miniaturizing Atomic Clock Technology for Space

PHARAO’s design is rooted in an atomic clock in Paris that occupies an entire room. The challenge of miniaturizing this complex technology into a system occupying less than a cubic meter, while ensuring its resilience to the intense conditions of a rocket launch and the harsh environment of space, was a significant engineering achievement.

The Science Behind PHARAO’s Accuracy

To generate a highly accurate time signal, PHARAO employs a process involving a fountain of caesium atoms, cooled to near absolute zero. It then observes their interaction with microwave fields. On Earth, such a system typically requires a device up to 3 meters in height. However, in the microgravity of space, these atoms can be projected in a slower, more compact fountain, enabling a significantly smaller apparatus.

Sensitivity and Measurement Precision

Simon Weinberg at ESA highlights the extreme sensitivity of the device, noting that even a teaspoon placed nearby could generate an electromagnetic field strong enough to disrupt the clock’s operation. “To put it in perspective, we are attempting to measure time to an accuracy better than one part in a thousand million millionth of a second,” Weinberg explains, emphasizing the immense difficulty of the undertaking.

ACES Project Timeline and Future

The conceptualization of ACES dates back to the 1990s, with initial plans for launch on the now-retired Space Shuttle program. Following its deployment in space, the first signal from ACES to reach an Earth-based clock is anticipated after an 18-month period. This timeframe includes approximately six months for device commissioning and a subsequent year dedicated to collecting measurements to isolate and eliminate noise from the clock signal.

Operational Lifespan and the Advent of Optical Clocks

ACES is projected to remain operational until 2030, coinciding with the planned deorbiting of the ISS. By this time, optical clocks, representing a new generation of ultra-precise timekeeping technology, are expected to largely supersede atomic clocks for terrestrial applications. However, their suitability for space deployment, particularly in terms of size and robustness, may still be under development.

Future Missions and Technology Advancement

Weinberg indicates that ESA intends to explore the development of a new generation of ACES to succeed the current mission on the ISS. This future endeavor will leverage the most advanced and appropriate technology available at that time. He acknowledges that realizing this ambition is a long-term prospect, requiring secured support, funding, and international collaboration.