ESA's Fluorescence Explorer (FLEX) and Copernicus Sentinel-3C were set to lift off together on 15 September 2026 aboard a Vega-C launcher from Europe's Spaceport in French Guiana, according to ESA. The agency reported on 14 September that both satellites had been encapsulated inside the launcher's nose cone and were awaiting liftoff.

At ESA's European Space Operations Centre (ESOC), two independent mission teams were rehearsing side by side to operate the spacecraft in parallel, including the moments when the two operations intersect. FLEX is ESA's photosynthesis mission, while Sentinel-3C is the third satellite for the Copernicus Sentinel-3 mission, monitoring Earth's oceans, land, ice and atmosphere.

ESA also marked the upcoming launch by publishing a set of facts about solar-induced fluorescence, the faint glow plants emit that gives scientists a way to study photosynthesis from space. Final preparations had seen the two satellites enclosed within the protective fairing of their Vega-C rocket ahead of the shared journey.