A Vega-C rocket lifted off from Europe’s Spaceport in French Guiana at 03:21 Central European Summer Time on 15 September carrying two European Space Agency satellites. Flight VV30 placed Copernicus Sentinel-3C in orbit first and FLEX about an hour later; the agency’s European Space Operations Centre received first signals from both, confirming their safe release and contact with the ground.
FLEX is the first satellite designed specifically to measure photosynthetic activity from space. Its Fluorescence Imaging Spectrometer detects the faint fluorescence plants give off as they absorb sunlight, a signal ESA describes as a direct indication of how efficiently vegetation is converting sunlight and carbon dioxide into energy. That distinction matters. A field of crops under drought stress can stay green for some time while its photosynthesis falls away, so a measurement of colour and a measurement of work are not the same measurement, and only one of them tells you what the land is contributing to the carbon and water cycles.
FLEX will fly in tandem with Sentinel-3A at first, and later with Sentinel-3C once that satellite is moved into position, so that the fluorescence readings can be paired with near-simultaneous observations of the atmosphere and land surface. Sentinel-3C itself carries instruments for ocean and land-surface temperature, ocean colour, sea and ice conditions, vegetation and inland water levels.
“Today’s launch is the culmination of years of scientific innovation, engineering excellence and international cooperation,” said Simonetta Cheli, ESA’s Director of Earth Observation Programmes. The instruments now have to be commissioned before any of that reaches a scientist’s desk.