At Europe's Spaceport in French Guiana, two Earth-observation satellites have been locked inside the protective fairing of a Vega-C rocket, setting the stage for a shared ride into orbit. The launch is scheduled for 15 September at 03:21 CEST, and the encapsulation marks the end of more than six weeks of on-site preparations.
A delicate stacking job
FLEX, ESA's Fluorescence Explorer, was the first to be placed inside the lower part of the Vespa secondary payload adapter, a system that lets the rocket carry multiple satellites at once. Sentinel-3C was then mounted on the upper part of the same adapter. The process required extreme precision, as the positioning ensures Sentinel-3C will be deployed first after reaching space.
Once both satellites were secure, the two halves of the rocket's fairing were closed and sealed. This shell protects the payload from the intense noise, vibrations, and aerodynamic forces of launch. For the teams who spent years building and testing the satellites, this moment was both technical and emotional.
Two missions, one goal
FLEX is designed to detect a faint glow emitted by plants during photosynthesis, a signal invisible to the human eye. Using a Fluorescence Imaging Spectrometer, it will measure this weak light from orbit. The data will help scientists understand plant health, vegetation stress, and how carbon and water move through ecosystems. The mission will produce global maps of fluorescence at a 300 by 300 meter resolution.
Sentinel-3C is the third satellite in the Copernicus Sentinel-3 series. It will continue systematic monitoring of Earth's oceans, land, ice, and atmosphere. Its instruments will measure sea-surface temperature and other key parameters, supporting climate and environmental studies.
Both satellites share a common purpose: to give researchers a sharper view of how our planet is changing. With the fairing sealed, the next step is liftoff, when the two spacecraft begin their separate but complementary journeys.
