COMPASSO – optical quantum technology for Europe's Galileo satellite navigation system

COMPASSO

With COMPASSO, the German Aerospace Center (DLR) is demonstrating a globally unique system of Galileo-relevant optical quantum technologies on the International Space Station ISS.

Quantum optical technologies are an essential element in plans for the further development of Europe’s Galileo satellite navigation system. However, proof is still needed that quantum technologies can withstand the performance requirements of the Galileo system under the challenging environmental conditions of space. This is the goal of the COMPASSO mission.

At its core, the COMPASSO system consists of three optical instruments: a highly stable iodine-based frequency reference (developed by DLR), a laser terminal for precise time and frequency transmission and distance measurements (developed by Tesat-Spacecom GmbH and DLR) and an optical frequency comb (developed by Menlo Systems GmbH). Combining the iodine reference with the optical frequency comb generates a highly precise and extremely stable time signal. This is then modulated onto a laser beam and transmitted from orbit to the optical ground station at DLR’s site in Oberpfaffenhofen. Researchers there analyse the signal, verify the accuracy of the time transfer and frequency stability, and determine the distance between the ground station and the space terminal with high precision.

The mission plan is to test these new technologies on the Space Station for two years, starting in 2027. Once COMPASSO arrives on the ISS, a robotic arm will install the payload onto a mounting slot on the Bartolomeo platform (developed by Airbus) located on the outside of the Space Station’s Columbus module.

Optical technologies – a key to secure and efficient satellite navigation and high-precision time distribution

Highly precise, reliable and robust quantum optical clocks and lasers (for data communication and high-precision distance measurement) are essential for the further development of the Galileo system and its services. In operational mode, Galileo satellites must be capable of functioning autonomously and without failure for at least 12 to 15 years. Instruments developed for use on future Galileo satellites must also be particularly lightweight and compact to withstand the forces and vibrations encountered during rocket launch.

Quantum optical clocks

Space-grade laser clocks could deliver even more accurate time information in the future, enhancing the efficiency and precision of Galileo’s precise navigation and time distribution services. Due to their higher oscillation frequencies, laser optical clocks are approximately 100 times more accurate than current microwave-based satellite clocks. In COMPASSO’s clock, the wavelength of a laser is tuned to a specific vibration of iodine molecules in a gas cell. The frequency of this oscillation depends exclusively on the quantum mechanical properties of iodine. This device-independent reference, in combination with a frequency comb, enables the clock’s high precision.

Optical inter-satellite links

The use of optical inter-satellite links (OISLs) in the Galileo constellation is a significant advance. These links enable data transmission and high-precision distance measurements between satellites, contributing to more accurate and robust orbit determination. OISLs also improve the autonomy of navigation constellations, making them less reliant on ground stations for uplinking control and mission data. In addition, optical links are more robust against eavesdropping and enable the distribution of quantum keys for increased security.

Applications beyond Galileo

The many advantages of quantum optical technologies open up a wide range of new applications for optical technologies in space, beyond Galileo. Examples include LEO-PNT (Low Earth Orbit Positioning, Navigation and Timing) systems and future generations of space-based communications and internet services. These technologies can also benefit scientific missions and projects such as EURIALO – a civil space-based system capable of providing continuous, global and independent air traffic surveillance – and environmental missions like GRACE-FO (Gravity Recovery And Climate Experiment Follow-On) and NGGM (Next Generation Gravity Mission).

They also open up new opportunities for applications, data architectures and communication infrastructures on the ground. Precise space-based time information is a largely ‘invisible resource’ for the economy and society, forming the basis of many technologies – from energy and communications networks to financial trading and industrial process control.

Background – the name ‘COMPASSO’
‘COMPASSO’ is derived from the first commercial scientific instrument developed by Galileo Galilei – a geometric and military compass. Designed in 1597, the device resembled a proportional divider with two ruler-like arms that could either move freely or be fixed in place using a semicircular arc, enabling precise measurements and calculations. Galileo’s invention had many applications and was used, among other things, as a precursor to the slide rule.

Background – the name ‘COMPASSO’

‘COMPASSO’ is derived from the first commercial scientific instrument developed by Galileo Galilei – a geometric and military compass. Designed in 1597, the device resembled a proportional divider with two ruler-like arms that could either move freely or be fixed in place using a semicircular arc, enabling precise measurements and calculations. Galileo’s invention had many applications and was used, among other things, as a precursor to the slide rule.