The European Space Agency (ESA) is on the verge of a revolutionary venture in observing our planet. The development of their latest mission from the Earth Explorer program, named FLEX (Fluorescence Explorer), has reached a key milestone that marks the transition from the development phase to the final preparation phase. At the facilities of the company Thales Alenia Space in Cannes, France, an extremely delicate operation was recently performed: the mission's unique and technologically advanced instrument was connected to the satellite platform that will carry it into orbit. This complex engineering task was successfully completed after the instrument, the heart of the entire mission, was delivered from the factory of the company Leonardo in Florence, Italy.

This joining represents the culmination of many years of work by hundreds of scientists and engineers across Europe and symbolizes a major step towards the launch scheduled for 2026. The FLEX mission promises to provide a completely new insight into the health of Earth's vegetation, in a way that has not been possible until now – by measuring the subtle glow that plants emit during photosynthesis.

FLORIS – The eye that will watch over the planet's health

The key element of the FLEX mission is its sole instrument, the Fluorescence Imaging Spectrometer, abbreviated as FLORIS. Designed and built with incredible precision, FLORIS has the task of mapping vegetation fluorescence on a global scale. Its measurements will allow scientists for the first time to directly quantify photosynthetic activity and assess the level of stress to which plants are exposed. Photosynthesis is, without a doubt, one of the most important biochemical processes on Earth; it is the foundation of life as we know it. It is the process by which plants, algae, and some bacteria convert sunlight, water, and carbon dioxide into energy for growth, releasing the oxygen we breathe. But, within this process, there is also a lesser-known phenomenon.

Specifically, while plants perform photosynthesis, they also emit a very faint red glow, known as solar-induced chlorophyll fluorescence. This glow is completely invisible to the human eye, but it carries invaluable information. The intensity of this fluorescence is directly related to the efficiency of the photosynthetic process. When a plant is healthy and has optimal conditions for growth – enough water, nutrients, and an ideal temperature – the level of fluorescence is stable. However, as soon as a plant is under stress, whether due to drought, disease, pollution, or lack of nutrients, the process of photosynthesis slows down, and this is almost instantly reflected in a change in the fluorescence signal. It is this change, this silent "cry for help" from vegetation, that the sensitive sensors of the FLORIS instrument will detect.

A revolution in monitoring global ecosystems

The ability of the FLEX mission to detect stress in plants before visible signs appear, such as a change in leaf color or wilting, represents a true revolution. Traditional methods of satellite vegetation monitoring rely on measuring "greenness," or the amount of chlorophyll, but such data is often delayed. By the time a leaf turns yellow, the damage has already been done. FLEX, on the other hand, will provide an early warning, allowing for timely interventions in agriculture and forestry.

The data it will collect will have a wide range of applications. In agriculture, it will help optimize irrigation and fertilization, leading to increased yields and reduced costs, and contributing to global food security in a world with an ever-growing population. For scientists studying climate change, data on global photosynthetic activity will provide key insights into the global carbon cycle. It will be possible to more accurately calculate how much carbon dioxide the world's forests and other ecosystems absorb from the atmosphere, which is crucial for developing more accurate climate models. Furthermore, the mission will help to better understand the impact of extreme weather events, such as heatwaves and droughts, on the health of ecosystems across the planet.

Synergy of European industry and science

The success of such a complex project rests on the cooperation and expertise of leading European technology companies. The role of the prime contractor was entrusted to the company Thales Alenia Space, which led the entire assembly, integration, and testing campaign of the satellite platform. This crucial phase took place in their advanced "clean rooms" in Belfast, Northern Ireland. After the platform was prepared, it was transported to Cannes where it awaited its "heart" – the FLORIS instrument.

The design and construction of this sophisticated instrument were entrusted to the Italian company Leonardo, a global leader in the field of space electro-optical systems. Their experts in Florence worked for years on developing a spectrometer that can detect extremely faint signals from an altitude of over 800 kilometers, while simultaneously filtering out all interference from sunlight reflected off the Earth's surface.

Now that the platform and the instrument are finally joined into a single entity, the satellite enters the final phase of rigorous testing. Engineers will conduct a series of checks to ensure that the satellite will withstand the extreme conditions of launch – strong vibrations and noise – and function flawlessly in the harsh environment of space, exposed to a vacuum and large temperature fluctuations. Every system, from power and communication to thermal control and the instrument itself, will be subjected to detailed tests. If everything goes according to plan, the FLEX satellite will be ready for its journey into orbit, where it will begin its four-year mission of observing the pulse of our planet.