Shortly before 11 o’clock in the evening on 7 March 2017, the tropical night air of French Guiana was rent with the roar of a Vega rocket, blasting off from its launch pad in Kourou. The payload sitting atop the rocket, a satellite developed and built by Airbus for the European Space Agency (ESA), was the missing piece in the puzzle to complete Europe’s colour-vision image of Earth.

Sentinel-2B joined its identical twin in polar orbit, unfurling its solar panels and reporting for duty just an hour after leaving Earth. Sentinel-2A, the first of the pair, launched in June 2015. Together, they make up Copernicus, the most ambitious Earth observation programme to date.   Positioned 180 degrees apart, the pair can complete a full circle of the Earth just 100 minutes. Working together, the Sentinel satellites can cover the whole world, including all land surfaces, large islands and inland and coastal waters, every five days.

Soaring at 786km above the surface of the Earth, the 1 tonne satellites snap optical images of our planet, recording everything from visible light photographs right through to short-wave, infra-red images. Each snapshot covers up to 290km, giving Europe a full, technicolour view of the world.  To ensure the clarity of the photographs, all of the telescopic lenses and mirrors on board the satellite are made from silicon carbide. This special material retains its rigid shape, even under the intense heat of the sun, keeping pictures crisp and sharp.

Sentinels keep watch over Earth

The data collected by the Copernicus Sentinels paints an accurate and real-time picture of our planet, allowing for remote monitoring of the condition and use of land; mapping natural disasters such as floods, forest fires and landslides; and even offers assistance in humanitarian aid missions.

With such high-resolution imaging capabilities, the Sentinel-2 mission is already proving invaluable to the management of food security here on Earth. Sentinels’ cameras can capture infra-red light, providing key information on vegetation state. Not only can the images be used to distinguish between crop types, they can also give information such as leaf coverage in rainforest canopies and even the water and chlorophyll content of leaves.

This plant data can then be used to monitor plant growth and inform decisions in agriculture, such as the amount of water or fertiliser needed to produce maximum crop yield. As well as the economic benefits to farmers, these images can help developing countries ensure food security.

Riding the SpaceDataHighway

In order to beam the images back to Earth, Sentinel-2 is rigged up to use the European Data Relay System, also known as the ‘SpaceDataHighway’. The system is a network of laser communication payloads spinning through space on geostationary and low Earth-orbit satellites. It is currently being developed by Airbus for ESA, and provides a fast and secure communication service to space.

As communications can be sent at light-speed back to Earth, the system allows for real-time monitoring of major events as well as making ideal for co-ordinating emergency response and security missions.

The Sentinel-2 satellites, as with their predecessors, the Sentinel-1 class, are the first observation satellites to be kitted out with Airbus’ new laser-tech. The EDRS-A was the first dedicated relay satellite for the communications system, launching into space in January 2016. The SpaceDataHighway opened to traffic in November 2016.

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