Launch is scheduled for tonight: 15 September at 03:21 CEST (14 September at 22:21 local time).

The satellites – two separate missions – will capture data about our changing global environment. While the FLEX mission will monitor the health of Earth’s vegetation, Sentinel-3C, together with the two Sentinel-3 satellites already in orbit, will monitor oceans, land, ice and atmosphere for Copernicus, the Earth observation component of the European Union’s Space Programme.

The launch vehicle is Europe’s Vega-C rocket. First, it will deploy Sentinel-3C, and then after some launcher manoeuvres, it will be followed by FLEX, which is fitted inside the Vespa+R payload adapter.

Find out how to watch the launch broadcast live here.

FLEX is an Earth Explorer mission – ESA’s fleet of small scientific satellites designed to explore different aspects of our Earth environment, from the magnetosphere to ice caps, and from biomass to the atmosphere. FLEX is dedicated to gathering data about the health of vegetation on a global scale. It does this by detecting the faint glow that is emitted by plants as they photosynthesise. Although not visible to the human eye, this fluorescence can be detected from space, providing an indication of whether plants are healthy or stressed by environmental conditions. The satellite’s Fluorescence Imaging Spectrometer can detect and measure this incredibly weak signal from an altitude of 814 km.

The mission is expected to produce global maps of vegetation fluorescence at a resolution of 300 m × 300 m, offering a new way to study how plants interact with the atmosphere and how carbon and water move through Earth’s ecosystems.

Since the first Sentinel-3 satellite was launched a decade ago, the mission’s data on oceans, land, ice and atmosphere have provided robust datasets for operational applications and scientific research, improving understanding of climate change and underpinning global climate policies. The launch of the mission’s third satellite heralds the continuity of this vital source of knowledge. Sentinel-3C carries four science instruments that capture data quickly across entire regions.

During the routine operations phase Sentinel-3 is managed jointly by Eumetsat and ESA on behalf of the European Commission.

The Vega-C programme is led by ESA, working with Avio as prime contractor and design authority. It ensures that Europe has versatile and independent access to space. Vega-C, which stands 35 m tall and can lift 2300 km into space, complements the Ariane family.

ESA leads the Vega-C programme, working with Avio as prime contractor and design authority. For this launch, flight VV30, Avio is also launch service operator.