ESA FLEX launch September 2026: Vega-C flight VV30 lifted off 14 September Kourou time (15 September CEST) with Sentinel-3C

ESA's Fluorescence Explorer, known as FLEX, was launched on a Vega-C rocket from Europe's Spaceport in Kourou, French Guiana. ESA's launch report says "Flight VV30 lifted off on 15 September at 03:21 (14 September at 22:21 local time)." Avio and the European Commission had announced the same moment as 01:21 UTC and designated the mission VV30. FLEX shared the rocket with the Copernicus Sentinel-3C satellite.^[7][8][9]

Hardware milestones through the northern summer tracked the schedule. ESA reported in early July that the two satellites had been shipped from Nice towards French Guiana, published an image of FLEX removed from its container at the spaceport on 21 July, and an image of FLEX being joined to its launch adapter on 21 August, captioned with the planned launch at 03:21 CEST on 15 September.^[4][10][11]

ESA describes FLEX as ESA's first satellite designed specifically to measure photosynthetic activity from space. When plants photosynthesise, they emit a very faint fluorescence, which ESA says "provides a direct indication of how efficiently vegetation is converting sunlight and carbon dioxide into energy." ESA frames the science goal as improving understanding of how carbon moves between plants and the atmosphere, and how photosynthesis affects the carbon and water cycles.^[1][9]

The measurement is made by the Fluorescence Imaging Spectrometer (FLORIS), which covers the 500-780 nm spectral range with fine sampling in the oxygen absorption bands. ESA lists the satellite's mass as 400 kg; Avio gives 397 kg. ESA's facts and figures list a sun-synchronous orbit at 814 km altitude, an inclination of 98.64 degrees and a 27-day repeat cycle, with a planned 3.5 years of operations after a three-month commissioning phase. Avio and ESA's Earth Online both describe FLEX as the eighth Earth Explorer mission under ESA's FutureEO programme.^[2][5][7]

The date is a common source of confusion. The same liftoff was 22:21 on 14 September in Kourou and 03:21 CEST on 15 September in Europe. Avio and the European Commission headlined the launch as 14 September, while ESA's launch report gives 15 September; all describe the same moment, 01:21 UTC.^[7][8][9]

Sharing a rocket with Sentinel-3C is not the whole relationship between the two missions. ESA says that initially FLEX will orbit in tandem with Sentinel-3A, and later Sentinel-3C will be moved to replace Sentinel-3A in the tandem formation. ESA's facts and figures put FLEX 40-100 km ahead of a Copernicus Sentinel-3 satellite, which provides additional measurements of the atmosphere and land surface used together with FLEX's fluorescence data.^[2][9]

Most of the mission description on this page comes from ESA. Avio, the launch service provider and a separate company from ESA, writes that "FLEX is the eighth Earth Explorer mission developed by ESA's FutureEO programme", which matches ESA's own Earth Online description.^[5][7][13]

A mass figure in launch coverage is easy to attach to the wrong spacecraft. Both Avio and the European Commission give about 1,143 kg, but that is the mass of Copernicus Sentinel-3C — not FLEX, whose mass ESA gives as 400 kg and Avio as 397 kg.^[2][7][8]

The instrument details — the FLORIS spectrometer and its 500–780 nm range — come from ESA material only.^[2][5]

ESA published the outcome on 15 September 2026. It says FLEX and Sentinel-3C "have been launched together aboard a Vega-C rocket from Europe’s Spaceport in French Guiana".^[9]

The deployment was sequential. A launch adapter called Vespa stacked both satellites inside the fairing, and "Positioned on top of Vespa, Sentinel-3C was injected into orbit first, followed by FLEX approximately one hour later." ESA's European Space Operations Centre then "received the all-important first signal from each satellite, confirming that both had been safely released from the rocket and had established contact with ground control." Avio's pre-launch release had given 116 minutes from liftoff to separation of the last satellite.^[7][9]

What the launch report does not establish. On 15 September ESA said controllers "will now spend the coming days conducting the ‘launch and early orbit phase’, meticulously checking and verifying the health and performance of both satellites". The confirmed result is orbit insertion and first contact. The cited ESA launch report does not report science data or instrument performance.^[9]

ESA describes FLEX as "ESA’s first satellite designed specifically to measure photosynthetic activity from space." The qualifier is "ESA’s first" and "designed specifically" — this page does not describe FLEX as the first measurement of plant fluorescence from orbit by any agency.^[9]

The instrument is the Fluorescence Imaging Spectrometer, which ESA says "will detect the extremely faint fluorescence emitted by plants as they absorb sunlight during photosynthesis." ESA calls the signal "invisible to the human eye" and says it "provides a direct indication of how efficiently vegetation is converting sunlight and carbon dioxide into energy."^[9]

FLEX is a research mission, not an operational service. ESA’s Director of Earth Observation Programmes, Simonetta Cheli, said that, developed within ESA’s FutureEO programme, FLEX is "a research mission that will advance our understanding of plant health and the role of photosynthesis in the carbon and water cycles". Sentinel-3C, by contrast, is the operational one — ESA calls it "the third satellite in the Sentinel-3 series".^[9]

Responsibility for Sentinel-3 is also split. ESA says that for the Sentinel-3 satellites "ESA is responsible for the development", and that "After the commissioning phase, the Sentinel-3 mission is jointly managed by ESA and Eumetsat", with Eumetsat responsible for routine spacecraft operations and marine and near-realtime atmospheric data, and ESA delivering land, cryosphere, inland water and offline atmospheric products. Naming a single agency as responsible for Sentinel-3C would be inaccurate.^[9]