Pascale Defraigne is head of the Time and Frequency Division at the Royal Observatory of Belgium. 

She received her Ph.D. in physics in 1995 at the Université Catholique de Louvain (UCL), Belgium, and then moved to the  Royal Observatory of Belgium where she started research projects on the use of geodetic GPS measurements for Time and Frequency transfer, first using the dual-frequency combinations of code measurements, and then on developments of PPP and IPPP. In the Consultative Committee of Time and Frequency, she chairs the working group on GNSS Time Transfer since 2012. She received the EFTF Award, "for seminal contribution in the use of geodetic GNSS techniques for time and frequency transfer" in 2012.  In parallel, Pascale Defraigne is involved in the Galileo Program as consultant for time and synchronization since 2013, she is Member of the International Astronomical Union since 2000, and in that frame, she was President of  commission Time 2006 to 2009.

She is now involved in the coordination of establishing a lunar reference Time, as chair of the CCTF task Group on Lunar Time.

What time is it on the Moon?

Pascale Defraigne - Royal Observatory of Belgium, Brussels, Belgium

Email: p.defraigne@oma.be

Abstract:

Given the renewed interest in lunar exploration, with applications requiring clock synchronization at the nanosecond level, adopting a relativistic lunar reference frame with an associated coordinate time becomes essential. The relativistic effects between an Earth-based clock and a Moon-based clock cannot be represented as a simple frequency offset, meaning that UTC cannot be directly used as a reference for high-precision applications.In this context, the international scientific community—including the organizations responsible for defining and regulating time standards—is working to define a lunar reference time scale and its relationship with UTC. Several options are currently being examined, each with its own advantages and drawbacks, informed by our experience on Earth.Ultimately, the scientific community will state —before the conference— on a unique definition of the lunar reference time, along with its practical realization, its calendar, and its traceability to UTC.

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Dr. Luigi Cacciapuoti graduated cum laude from the University of Napoli “Federico II” and obtained his PhD from the Firenze University. 

He began his research career in Firenze, where he worked on ultracold atoms and matter-wave interferometry, and later continued at the Institut für Quantenoptik of the Leibniz University in Hannover studying the coherence properties of elongated Bose–Einstein condensates. He subsequently joined BNM-SYRTE at the Observatoire de Paris, contributing to research on atomic fountain clocks and high-precision time & frequency metrology. In 2004, he joined the European Space Agency, where he has since contributed significantly to the development of atomic quantum sensors and precision measurement technologies for space applications. He is serving as Project Scientist for several fundamental-physics missions and studies, including the Atomic Clock Ensemble in Space (ACES), Space Optical Clocks (SOC), and the MoonLIGHT Pointing Actuator (MPAc). Dr. Cacciapuoti’s research spans cold-atom physics, atom interferometry, Bose–Einstein condensation, and quantum sensors for fundamental physics tests on Earth and in space. 

He collaborates with the Firenze University on the MEGANTE experiment, a large-scale atom interferometer dedicated to measuring the Newtonian gravitational constant G, performing precision gravimetry, and testing the Universality of Free Fall. 

ACES: First Results from Space

Luigi Cacciapuoti - European Space Agency (ESA), Directorate of Science

Email: luigi.cacciapuoti@esa.int 

Abstract: 

On 21 April 2025, the Atomic Clock Ensemble in Space (ACES) payload was launched to the International Space Station (ISS) and installed at the external payload facility of the Columbus module. Since then, the PHARAO clock, which uses laser cooled cesium atoms to generate a signal with a predicted stability and accuracy of 1-210-16, is compared to atomic clocks on ground by means of two time and frequency transfer systems: a link in the microwave domain (MWL) and a pulsed optical link (ELT). The ACES microwave link is expected to deliver comparisons of clocks to a few parts in 1017, opening unique opportunities to test general relativity, constrain dark matter models, and develop applications in relativistic geodesy, time & frequency metrology, and timescales distribution. ACES is currently completing its in-orbit commissioning. During this phase, the PHARAO clock is optimized in terms of frequency stability, the on-board links are characterized, and the accuracy evaluation of PHARAO is initiated using MWL comparisons with ground-based atomic clocks. Connected to the ground terminals of the ACES MWL, the atomic clocks operated by LTE in France, PTB and Wettzell in Germany, NPL in the United Kingdom, JPL and NIST in the United States, and NICT in Japan are contributing to the ACES clock network. The ACES ground segment is then completed by satellite laser ranging stations connecting their clocks to ACES via the ELT optical link. The commissioning activities are expected to be concluded before the end 2025, thus releasing ACES to start the routine science phase. In this paper, we will present the first space-based results of the ACES mission, including the PHARAO characterization measurements, the ACES links performance evaluation, and the first comparisons of the PHARAO clock with atomic clocks on ground.

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