The European Space Agency (ESA) has confirmed exceptional success in demonstrating a revolutionary technology that will forever change the way we communicate with deep space missions. During the summer of 2025, a series of four successful optical communication tests were conducted with NASA's Psyche spacecraft, which is currently at a distance of more than 300 million kilometers from Earth. All four attempts to establish a laser link, each technically more demanding than the last, were crowned with complete success, demonstrating Europe's readiness for a new era of interplanetary internet.

This technological feat is not just a test; it represents a key step towards a future where vast amounts of data, including high-resolution videos and complex scientific data, can be sent from Mars, Jupiter, and beyond in near real-time. Unlike traditional radio-frequency (RF) waves, which have been used for decades, laser beams offer significantly higher data transmission rates, enabling the sending of high-resolution scientific information, videos, and telemetry in volumes previously unimaginable. Optical communication uses photons of light to transmit information, which allows for much narrower and more concentrated beams, thereby reducing signal loss over vast distances and requiring smaller and lighter communication systems on the spacecraft themselves.

A historic laser signal from Europe to deep space

The first key moment in this ambitious campaign occurred on July 7, 2025. That evening, ESA's portable Ground Laser Transmitter (GLT), temporarily installed at the Kryoneri Observatory in Greece, fired a precisely aimed laser beam towards the calculated position of NASA's Psyche spacecraft. The spacecraft, launched to explore the eponymous metallic asteroid believed to be the remnant of an ancient protoplanet's core, became an ideal partner in this pioneering venture thanks to the experimental Deep Space Optical Communications (DSOC) system from NASA that it carries.

After about fifteen minutes, the time it took for light to travel the immense distance, the DSOC instrument on Psyche successfully detected the incoming signal. Almost instantly, the system responded with its own laser beam directed back towards Earth. This return signal was captured by ESA's Ground Laser Receiver (GLR), located at the Helmos Observatory, about 37 kilometers from the transmitter in Kryoneri. The entire communication loop, from sending to receiving a response, lasted about 30 minutes and thus made history as the first successful optical link with a deep space spacecraft achieved from European soil. For the purposes of the campaign, these two Greek observatories, normally intended for astronomical observations, were temporarily repurposed into a powerful communication duo.

Persistence and stability: Maintaining a connection at cosmic distances

Following the initial success, the ESA teams focused on the next, even greater challenge: maintaining a continuous and stable connection with a spacecraft moving at high speed. The next two tests were dedicated to just that. "These attempts allowed us to provide the spacecraft with the most stable possible terrestrial laser 'beacon', so that it could reliably send data to our receiver on Earth," explained Clemens Heese, Head of ESA’s Optical Technologies Section and project manager for the DSOC demonstration.

The effort paid off. The technique worked flawlessly, and during the third attempt, the team managed to receive an uninterrupted stream of data at a rate of 1.3 megabits per second (Mbps). They successfully decoded all the received information that arrived from a distance approximately twice that of the Earth from the Sun. Achieving such stability at such an extreme distance required incredible pointing precision and constant corrections to compensate for the Earth's movement, the planet's rotation, and the spacecraft's own trajectory.

The campaign's climax: Hunting for photons and the cat that conquered the solar system

The fourth and final test pushed the boundaries of what is possible. This time, the receiver at the Helmos Observatory tracked the spacecraft while it was low on the horizon, meaning the signal had to pass through a denser and more turbulent part of the Earth's atmosphere. Atmospheric turbulence is the greatest enemy of optical communication because the "twinkling" of the beams can cause a loss of connection. Despite this, the sophisticated system at Helmos, whose detector was cooled to a temperature of just 1 Kelvin (-272.15 °C) to be able to register individual photons, successfully tracked Psyche.

Unlike previous transmissions that contained test data, this one brought an unexpected and charming surprise. From a distance of over 300 million kilometers, at a speed that reached up to 1.8 Mbps, came a video of a cat named Tater chasing a laser dot. This move, conceived by NASA's Jet Propulsion Laboratory (JPL), was not just a joke, but a clever demonstration of the system's ability to transmit high-definition video over interplanetary distances, opening the door to future live broadcasts from other planets.

Andrea Di Mira, project manager for ESA’s GLT, emphasized the complexity of this operation: "With the fourth link, we crossed the threshold of two astronomical units. This required an extremely complex operation with parallel activities. The round-trip signal time of about 34 minutes left us very little room to adjust the laser pointing angles. We planned every activity carefully, prepared backup scenarios, and precisely calibrated each system to align our high-power beams with an accuracy of one arcsecond and keep them stably pointed at Psyche."

Complex orchestration behind the scenes

During all four tests, the Helmos Observatory served not only as the home for the receiver but also as ESA's main operational center. From there, the team coordinated each pass of the spacecraft, including communication between the GLR, the GLT, and the DSOC flight terminal team at JPL in Southern California. Due to the vast distances and signal delays, every action had to be anticipated and coordinated in advance.

"It was like conducting an orchestra: every move had to be perfectly timed so that each decision would bring us closer to the optimal point for tracking Psyche and maximizing signal reception," said Sinda Mejri, project manager for ESA’s GLR. "The flight terminal team at JPL continuously sent us signal strength metrics from the spacecraft back to Greece, while we executed a predefined decision tree to adjust scan patterns and beam pointing."

A look to the future: From data analysis to missions to Mars

After the successful completion of the campaign, the collected data will be subjected to detailed analysis to evaluate the performance of each system and further refine the technology. An upgrade of the Helmos telescope is planned to improve its capabilities, and future activities for the GLT transmitter are also being considered. Discussions are already underway about potential new experiments in the sky during 2026.

Mehran Sarkarati, Head of ESA's Ground Station Engineering department, highlighted the strategic importance of this success: "Autonomous and resilient connectivity is crucial for sovereignty, not only on Earth but also in space. This demonstration marks a key step towards establishing European access to high-capacity optical communication networks for the Moon, Mars, and beyond." This success lays the foundation for ESA's proposed ASSIGN (Advancing Solar System Internet and GrouNd) programme, which will be presented at the ESA ministerial council in November.

Looking even further into the future, ESA is currently studying the concept of an electric-propulsion Martian tug, called 'LightShip', which would transport crewed spacecraft to Mars. After dropping off the passengers, LightShip would move into a service orbit from where it would provide communication and navigation services via the MARCONI (MARs COmmunication and Navigation Infrastructure) system. Part of that system will also include an optical communication demonstrator, as a step on the path towards supporting future human missions to the Red Planet.