The European Space Agency expects to launch its FLEX photosynthesis mission and the Copernicus Sentinel-3C Earth-observation satellite together on a Vega-C rocket from French Guiana on 14 September 2026.

The launch, designated Vega-C flight VV30, is scheduled for 22:21 local time from Europe’s Spaceport. That corresponds to 03:21 CEST on 15 September. The date and time remain a plan rather than a completed launch.

FLEX is designed to measure a faint optical signal emitted by plants as they absorb sunlight. Sentinel-3C, the third satellite in the Sentinel-3 series, is intended to provide near-real-time observations of the ocean, land, ice and atmosphere.

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A launch combining two observation missions

The two satellites have different scientific roles. FLEX is an ESA Earth Explorer mission focused on photosynthesis, while Sentinel-3C is part of the European Union’s Copernicus Earth-observation programme.

Vega-C is described by ESA as a 35-metre-tall rocket weighing 210 tonnes on the launch pad. It uses three solid-propellant stages followed by a fourth liquid-propellant stage. For VV30, the upper stage is intended to carry out two precise orbital drop-offs, deploying the two spacecraft during the mission.

ESA leads the Vega-C programme, with Avio as prime contractor and design authority. Thales Alenia Space is the prime contractor for both FLEX and Sentinel-3C. Leonardo provided FLEX’s Fluorescence Imaging Spectrometer, the instrument responsible for its principal measurement.

If the launch and deployments succeed, the mission would put two complementary types of environmental observation into orbit: one focused on a biological process in vegetation and the other on broad physical conditions across Earth’s surface and atmosphere.

What FLEX will measure

FLEX carries the Fluorescence Imaging Spectrometer, which is designed to detect faint fluorescence emitted by plants as they absorb sunlight. ESA says the signal is invisible to the human eye and varies with plant health and environmental conditions.

This fluorescence is a weak re-emission of absorbed light from photosynthetic tissues. Changes in the signal can provide information about photosynthetic function and plant stress. However, the signal is not a direct visual image of plant health: it requires calibrated remote-sensing measurements and scientific interpretation.

ESA says FLEX is intended to provide global information about vegetation health and photosynthetic activity. Such measurements could help researchers study how vegetation responds to environmental conditions, but the supplied pre-launch announcement does not report any measurements or results from the mission.

That distinction is important. FLEX’s scientific value is currently a planned capability, not an in-orbit result. Its actual performance will depend on instrument sensitivity, calibration, coverage and the quality of validation after launch.

Sentinel-3C’s Earth-observation role

Sentinel-3C is intended to extend the Sentinel-3 series within Copernicus, the European Union’s flagship Earth-observation initiative. ESA describes Copernicus as being overseen and financed by the EU in partnership with ESA.

The satellite’s listed measurements include:

  • ocean height;
  • sea-surface and ice-surface temperatures;
  • ocean colour;
  • sea-ice thickness;
  • vegetation;
  • wildfires;
  • ice sheets; and
  • water levels in inland lakes and rivers.

ESA says these observations are intended to provide near-real-time information for monitoring ocean, land, ice and atmosphere conditions, supporting weather forecasting and climate science.

“Near-real-time” is a general description in the announcement rather than a detailed latency specification. ESA’s release does not provide a numerical delivery time, spatial resolution, revisit period or orbital parameters for Sentinel-3C. It also does not report operational data from the satellite, which has not yet launched.

The satellite is therefore best understood at this stage through its planned role in the Sentinel-3 and Copernicus systems. The supplied material does not include a detailed comparison between Sentinel-3C and earlier Sentinel-3 spacecraft.

Sources

  • European Space Agency, “Media invitation: FLEX and Copernicus Sentinel-3C online media briefings” — https://www.esa.int/Newsroom/Press_Releases/Media_invitation_FLEX_and_Copernicus_Sentinel-3C_online_media_briefings