ESA Top Multimedia

ESA’s state-of-the-art Biomass satellite launched aboard a Vega-C rocket from Europe’s Spaceport in Kourou, French Guiana. The rocket lifted off on 29 April 2025 at 11:15 CEST (06:15 local time).

In orbit, this latest Earth Explorer mission will provide vital insights into the health and dynamics of the world’s forests, revealing how they are changing over time and, critically, enhancing our understanding of their role in the global carbon cycle. It is the first satellite to carry a fully polarimetric P-band synthetic aperture radar for interferometric imaging. Thanks to the long wavelength of P-band, around 70 cm, the radar signal can slice through the whole forest layer to measure the ‘biomass’, meaning the woody trunks, branches and stems, which is where trees store most of their carbon.

Vega-C is the evolution of the Vega family of rockets and delivers increased performance, greater payload volume and improved competitiveness.

Access the related broadcast quality video material. 

The European Space Agency’s Proba-3 mission has achieved its ambitious goal when its two spacecraft, the Coronagraph and the Occulter, flew 150 metres apart in perfect formation, simulating a single giant spacecraft.

Earlier this year, the first step of the mission was successfully completed. The operations team, consisting of engineers from ESA and its closely collaborating industrial partners, came together at the Agency’s European Space Security and Education Centre in Redu, Belgium.

Using a set of positioning instruments, they were able to align the two spacecraft in formation, and monitor them as they maintained their relative position autonomously.

Now, following more finetuning and testing, the team has achieved the desired precision, making Proba-3 the world’s first-ever precision formation flying mission.

The mission relies on several innovative technologies, many of which are technology demonstrations developed through ESA’s General Support Technology Programme (GSTP). “To do something that has never been done before, we needed to develop new technologies,” notes Esther Bastida Pertegaz, Proba-3 systems engineer.

“The formation flying is performed when the spacecraft are more than 50 000 km above Earth,” explains Raphael Rougeot, Proba-3 systems engineer.

“Here, the Earth’s gravity pull is small enough, so that very little propellant is needed to maintain the formation. Then the formation is broken and needs to be acquired again over the next orbit, in a repeated cycle.”

The ultimate goal is for the two spacecraft to align with the Sun so that the 1.4-m large disc carried by the Occulter casts a 5-cm shadow onto the optical instrument on the Coronagraph, allowing it to study the faint solar corona.

Teodor Bozhanov, formation flying system engineer, explains further: “The initiation of this formation-flying repetitive sequence is performed by the ground control centre, with the operations team obtaining position information to determine the exact location of the two satellites in space. The mission’s thrusters are then used to bring them closer together.

“All the rest is done autonomously. The spacecraft measure and control their relative position using the Visual Based System, which includes a wide-angle camera on the Occulter tracking a set of flashing LED lights on the Coronagraph.

“Once the satellites get close enough to each other, a narrow-angle camera locking onto the same set of lights enables a more accurate positioning.”

Raphael describes the last step needed to close the precision gap: “Although we were previously able to perform formation flying using only the camera-based systems on board, we were still missing the desired precision.

“Two major achievements have been key to unlocking it. First, it was the calibration of the on-board laser instrument, and its integration into the full formation flying loop.”

“This laser instrument, called the Fine Lateral and Longitudinal Sensor (FLLS), enables relative positioning down to a millimetre accuracy,” adds Jorg Versluys, Proba-3 payloads manager. “It consists of a laser beam fired from the Occulter spacecraft and reflected in the Coronagraph’s retroreflector back to the Occulter, where it is detected.”

“The second crucial achievement was successfully using the shadow position sensor,” Raphael continues. “An on-board algorithm based on the measurement of light intensity around the coronagraph aperture ensures that the Coronagraph spacecraft stays in the shadow cast by the Occulter spacecraft.”

Esther notes: “Combining all these sensors, and thanks to the on-board software managing all the spacecraft systems and providing Navigation, Guidance and Control functions, the formation is stable beyond expectations.”

Damien Galano, Proba-3 project manager, concludes: “We are talking about millimetric accuracy in range, and sub-millimetric in the lateral position. We can’t wait to see the completion of the instrument calibration and the first processed image of the Sun’s corona.”

Forests play an important role in the global carbon cycle, influencing levels of carbon dioxide in the atmosphere – and therefore climate change. By measuring the amount and change in the carbon-rich biomass contained in tree trunks and branches, satellites provide valuable insights into how these ecosystems are changing.

ESA’s Climate Change Initiative Biomass project has merged observations from multiple satellites to provide annual global maps of above-ground biomass between 2007–2022. These insights are vital for modelling the carbon cycle, guiding forest management, and supporting national greenhouse-gas reporting.

ESA’s state-of-the-art Biomass satellite has launched aboard a Vega-C rocket from Europe’s Spaceport in French Guiana. The rocket lifted off on 29 April 2025 at 11:15 CEST (06:15 local time).

In orbit, this latest Earth Explorer mission will provide vital insights into the health and dynamics of the world’s forests, revealing how they are changing over time and, critically, enhancing our understanding of their role in the global carbon cycle. It is the first satellite to carry a fully polarimetric P-band synthetic aperture radar for interferometric imaging. Thanks to the long wavelength of P-band, around 70 cm, the radar signal can slice through the whole forest layer to measure the ‘biomass’, meaning the woody trunks, branches and stems, which is where trees store most of their carbon.

Vega-C is the evolution of the Vega family of rockets and delivers increased performance, greater payload volume and improved competitiveness.

Access the related broadcast quality video material.

ESA’s state-of-the-art Biomass satellite launched aboard a Vega-C rocket from Europe’s Spaceport in Kourou, French Guiana. The rocket lifted off on 29 April 2025 at 11:15 CEST (06:15 local time).

In orbit, this latest Earth Explorer mission will provide vital insights into the health and dynamics of the world’s forests, revealing how they are changing over time and, critically, enhancing our understanding of their role in the global carbon cycle. It is the first satellite to carry a fully polarimetric P-band synthetic aperture radar for interferometric imaging. Thanks to the long wavelength of P-band, around 70 cm, the radar signal can slice through the whole forest layer to measure the ‘biomass’, meaning the woody trunks, branches and stems, which is where trees store most of their carbon.

Vega-C is the evolution of the Vega family of rockets and delivers increased performance, greater payload volume and improved competitiveness.

Access the related broadcast quality video material.

ESA’s state-of-the-art Biomass satellite has launched aboard a Vega-C rocket from Europe’s Spaceport in French Guiana. The rocket lifted off on 29 April 2025 at 11:15 CEST (06:15 local time).

In orbit, this latest Earth Explorer mission will provide vital insights into the health and dynamics of the world’s forests, revealing how they are changing over time and, critically, enhancing our understanding of their role in the global carbon cycle. It is the first satellite to carry a fully polarimetric P-band synthetic aperture radar for interferometric imaging. Thanks to the long wavelength of P-band, around 70 cm, the radar signal can slice through the whole forest layer to measure the ‘biomass’, meaning the woody trunks, branches and stems, which is where trees store most of their carbon.

Vega-C is the evolution of the Vega family of rockets and delivers increased performance, greater payload volume and improved competitiveness.

Access the related broadcast quality video material.

The Atomic Clock Ensemble in Space (ACES), ESA’s state-of-the-art timekeeping facility, is now installed on the Columbus laboratory of the International Space Station. This still image, captured by external cameras on the Station, shows ACES after installation. For 25 years, cameras on the Station have documented activities in orbit, providing real-time views of operations like this one – a rare and remarkable perspective from space. 

On 25 April, the Canadian Space Agency’s robotic arm carefully extracted ACES from the SpaceX Dragon trunk and secured it onto the Columbus External Payload Facility, next to ESA’s space storm hunter ASIM (Atmospheric-Space Interactions Monitor). Mounted on the Earth-facing side, ACES will connect with ground clocks worldwide as the Station orbits Earth sixteen times a day. 

Developed by ESA with European industry led by Airbus, ACES carries the most precise clocks ever sent to space: PHARAO, developed by the French space agency CNES, and the Space Hydrogen Maser from Safran Timing Technologies in Switzerland. Together with a sophisticated microwave and laser link, they will compare time between space and Earth with unprecedented accuracy, testing fundamental physics and advancing future time standards. 

In March 2025, ACES arrived at NASA’s Kennedy Space Center, where ESA, Airbus and NASA teams prepared the payload for flight. ACES launched on 21 April aboard a SpaceX Falcon 9 as part of the 32nd commercial resupply services mission to the International Space Station. Today, ACES was successfully switched on for the first time, establishing communications with ground control and stabilising its thermal systems in preparation for clock operations. 

A six-month commissioning phase now begins, after which ACES will embark on its two-year science mission, opening new frontiers in fundamental physics and timekeeping.