‘SpaceDataHighway’ – Why and How?

A satellite in LEO can downlink data only when visible from ground station
A satellite in LEO can downlink data only when visible from ground station

A satellite in Low Eart Orbit, LEO, can cover just one certain area of the Earth’s surface at a time. The same thing goes when it comes to contacting the satellite. To download data from the satellite, or to send commands to the satellite is possible only during the few minutes each orbit it passes right over, or close to, the ground station.

Effective and sharp-eyed Earth Observation Satellites, EOS, give us every week more information than earlier would have taken years to collect. Information to build the foundation for the decisions we make. Sometimes, getting data in near real time would come in handy.

A satellite in Geostationary orbit, GEO, though, is easily contacted 24/7 from a single disc. That’s why telecom satellites are placed in GEO. On the other hand – from a distance about 36000 kilometres from the Earth’s surface it’s more difficult to collect accurate data.

Almost half the globe is visible from one single satellite in Geostationary orbit.

By doing the math, you find that a satellite at an altitude of about 800 km above the Earth’s surface is able to “see” an area with a radius of about 3000 km. A satellite in GEO covers almost half the planet Earth.

Mathematical answers

Think of the possibility to track a tsunami. In theory, the technique is already launched. Then think of having to spend time waiting for the satellite to pass a certain ground station before the data packages can be downloaded, which, of course, will delay the warning. More data and more images in higher resolution increase the need to improve the data traffic in space. The European Data Relay System system, EDRS, is about to open up a data highway in space – and from space to ground.

A satellite in GEO has optical contact with any satellite in LEO, at least, half the time.

EDRS gives us the possibility to combine Earth observation and telecommunication. Data from a Sentinel satellite or the International Space Station can be sent via the EDRS to a satellite in GEO using a fast optical link. Then the data is transmitted from the GEO satellite down to its disc on Earth.  The first laser node was launched January 29th, from Baikonur in Kazakstan and the EDRS-A, on board the telecom satellite Eutelsat 9b.

EDRS. Image: ESA

There sure is a need for speed. The ESA Copernicus Earth observation program is good for about 60 Terabytes of data every day. In 2022, the ESA Earth observation archives volume projection is exceeding 50 Petabyte, 50 000 Tb, annually.

Now read this: Observing the Earth’s climate 1/2


JanJan teaches mathematics and interdisciplinary science to pupils 13-16 years of age at Sursik School, Pedersöre, Finland. Space-related science often gives some sort of answer to the question “Why?”, a question quite common in math class. It also triggers curiosity, one key component in progress.

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