Leonardo to Design Next Generation Atomic Clock for Galileo Satellites

March 28, 2024

The European Space Agency (ESA) has signed a €12 million contract with Leonardo S.p.A (Italy) and Istituto Nazionale di Ricerca Metrologica to design a new atomic clock for Galileo — Europe's satellite navigation system.

Atomic clocks are the main enabler of system performance and positioning accuracy for Galileo satellites. Under the new contract, Leonardo S.p.A will serve as the prime and Istituto Nazionale di Ricerca Metrologica (INRiM) as subcontractor. The two companies will work with ESA to develop a pulsed optically pumped rubidium atomic clock.

“The pulsed optically pumped rubidium atomic clock under development combines the robustness of rubidium vapor cell atomic clocks, largely used in satellite navigation constellations like Galileo, with state-of-the-art optical and digital technologies,” explains Manuela Rapisarda, GNSS Evolutions Payload Principal Engineer at ESA.

The contract requires Leonardo S.p.A to design, manufacture, test and qualify an engineering qualification model, after which an experimental flight model is expected to fly on a Galileo Second Generation (G2) satellite for early in-orbit verification. After initial tests, the new clock will still be monitored to study its reliability and long-term lifetime. Experimental clocks will fly in addition to the operational clocks that are used in the provision of Galileo services.

Galileo is one of the most crucial space-based infrastructures in Europe. “If qualified, the new clock technology will not only contribute to improving its performance but will guarantee Europe to stay at the forefront of atomic clock technology,” says Pascale Flagel, Head of Galileo and EGNOS Evolution Division.

The capability of a satellite navigation system to pinpoint a location stems from calculating the time it takes for a signal to travel from the satellite to a receiver. Galileo satellites orbit at more than 23,000 kilometers (km) above Earth, transmitting signals that incorporate a time stamp. Since the propagation speed of the signal is known, the difference between the transmission and reception time determines the distance of the user with respect to the satellite. It is possible to determine the user position on Earth knowing its distance from at least four satellites.

The signal transmitted by the satellite takes around a twelfth of a second to reach the user on Earth. Positioning accuracy is therefore linked to Galileo’s timing precision which needs to be within few nanoseconds – billionths of a second – in order to have a positioning accuracy of meters.

Currently, Galileo satellites of the first generation carry passive hydrogen masers, also developed by Leonardo, and rubidium clocks, supplied by Safran. The new alternative atomic clock technology subject of the signed contract is expected to be even more precise, with a decrease in energy consumption and a mass reduction of more than 40 percent with respect to the existing Galileo passive hydrogen maser clocks.

ESA's confirmation of the development of the new atomic clock comes several months after Airbus began production on the six G2 satellites that will form the Galileo Second Generation constellation in Friedrichshafen, Germany. Each G2 satellite will incorporate six (rather than four) of the atomic clocks being developed by Leonard S.p.A.

In addition to the new atomic clock technology, the G2 satellites — which weigh over 2 tons — are equipped with electric propulsion and inter-satellite links, enabling them to communicate and cross-check with one another. Airbus is on track to deliver launch-ready G2 satellites to ESA by 2026.

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