Sentinel-3C

Sentinel-3C and FLEX will fly together on a Vega C rocket

The Sentinel-3C mission will be carried out by Arianespace using a Vega C rocket, and its main objective is to launch two European Earth observation satellites: Copernicus Sentinel-3C and Fluorescence Explorer, FLEX. The launch is scheduled for September 15, 2026, at 03:21 CEST from the Guiana Space Centre in French Guiana.

The two spacecraft have different scientific tasks, but both belong to the European system for observing our planet. Sentinel-3C will continue systematic measurements of oceans, land, ice, and the atmosphere, while FLEX is intended to enable observation of the very faint fluorescence emitted by plants during photosynthesis.

Sentinel-3C will expand the Copernicus programme constellation

Sentinel-3C is the third satellite in the Sentinel-3 series. Its instruments will provide data on, among other things, sea surface temperature, ocean colour, sea level, and sea ice characteristics. Altimetric, thermal, and optical observations will also make it possible to monitor vegetation, fires, and changes in the height of inland waters and ice cover.

Data from the Sentinel-3 constellation are used by the European Copernicus programme. Their importance stems, among other things, from the ability to conduct regular measurements of the same parameters on a global scale. Sentinel-3C will enhance the ability to continue such observations and maintain long-term Earth measurement series.

FLEX will complement these data with a parameter not measured by standard imaging instruments. The Fluorescence Imaging Spectrometer is designed to detect faint plant fluorescence radiation and create global maps of this phenomenon at a resolution of 300 × 300 metres. Fluorescence intensity changes with photosynthetic activity and environmental conditions, so the measurements are expected to provide information on the health and stress of vegetation.

Two satellites under a single Vega C fairing

A distinctive feature of this launch is the use of the Vespa adapter, which allows the Vega C rocket to carry more than one large payload. FLEX was placed in the lower part of the adapter, while Sentinel-3C was mounted above it. This configuration was designed so that Sentinel-3C would be separated from the rocket first.

After integration was completed, both satellites were enclosed in Vega C's shared aerodynamic fairing. During the first minutes of flight, it protects the payload from atmospheric flow, vibrations, and the very high noise levels generated during rocket operation. Once the appropriate altitude is reached, the fairing will be jettisoned.

The launch will take place from the ELA-1 complex at the Guiana Space Centre. Combining Sentinel-3C and FLEX in a single mission distinguishes this flight from a typical launch of an individual satellite. One Vega C launch will simultaneously begin the continuation of Copernicus operational observations and a new ESA scientific mission dedicated to studying plant photosynthesis from orbit.