FLEX Fueled: Europe’s Satellite for Measuring Photosynthesis Poised for Launch

Fueled and in the final phase

At Europe’s spaceport in Kourou, French Guiana, the Earth-observation satellite FLEX has completed a key pre-launch step: it has been fueled. With that milestone behind it, the launch is within reach. Liftoff is scheduled for 15 September at 03:21 CEST (14 September, 22:21 local time in Kourou). The propellant is required to reach and maintain orbit, to control attitude, and for any necessary orbital adjustments.

A window into plant function

FLEX measures solar-induced chlorophyll fluorescence (SIF) — an extremely weak light signal that plants emit during photosynthesis. Unlike conventional satellite images, which mainly capture leaf area or vegetation indices, SIF provides information on current physiological activity: how efficiently plants are taking up CO2 and how their metabolism is responding.

Early stress signals and better carbon budgets

Observing vegetation functionality in near real time offers concrete advantages: stress from drought, heat or nutrient deficiency can often be detected before visible damage appears. When combined with established Earth-observation data, SIF improves estimates of CO2 uptake by ecosystems and reduces uncertainties in the global carbon cycle.

Synergies with existing missions

FLEX is designed to link its measurements with data on temperature, humidity, land cover and reflected sunlight. This integration enables a more comprehensive understanding of plant function and environmental stress, and strengthens modelling and predictions of how ecosystems respond to climate extremes.

Benefits for practice and conservation

In agriculture, early indications of declining photosynthesis can inform decisions on irrigation, fertilization and harvest timing. Forestry operations and protected-area managers gain indicators of emerging health problems in stands — including in regions with scarce ground data.

Technology and the path to data availability

After launch, the satellite will undergo deployment, commissioning and instrument calibration. Data will only be available for research and applications after these tests are completed. Because SIF measurements are sensitive to disturbances, they will be closely validated against ground observations and airborne campaigns.

Importance for climate research

Plants and soils absorb a substantial share of human-made CO2 emissions, but their uptake capacity fluctuates under influences such as heat, drought or fire. FLEX data will help better quantify actual CO2 sequestration and the resilience of ecosystems. In turn, this can make climate models and emission inventories more robust.