First gigabit transmission of data in orbit

Laser transmits image data over more than 36, 000 kilometers away

Laser Liniks connect near-Earth satellites with a geostationary satellite and this sends the data to Earth. © ESA
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Laser Link in Orbit: Over nearly 36, 000 kilometers, two satellites in orbit have been transmitting data by laser. This laser link made it possible for the first time to retrieve data from a low orbit earth observation satellite even if it is not flying over a receiving station. At 0.6 Gigabit, the transfer was faster than ever before.

At the moment, observational data from satellites in near-Earth orbit can only ever be sent if the satellite is actually flying over a station. Until then, the data must be stored and are therefore not available to the user. To change that, the European Space Agency (ESA) has developed a laser-based transmission system: the European Data Relay System (EDRS). With this, the satellites should also be able to pass on their data to one another and thus make their data constantly available.

Laser beam with 30x data rate

How well this works has now shown the first long-range transmission of image data in orbit. Sender was the European earth observation satellite Sentinel 1A, which since April 2014 orbited the poles in about 700 kilometers in so-called near-Earth orbit. This satellite has transmitted its data to the Alphasat I-XL communications satellite using the on-board Laser Communication Terminal (LCT), which has been orbiting in geostationary orbit 36, 000 kilometers since July 2013.

The Laser Communication Terminals (LCT) transmit laser data through the orbit © ESA

The laser connection between Alphasat and Sentinel 1A can theoretically carry data volumes of up to 1.8 gigabits per second over a distance of up to 45, 000 kilometers. "That's equivalent to 180 DVDs per hour, " explains Rolf Meyer from the German Aerospace Center (DLR), who helped develop the system. The data rate is 30 times higher than usual today. "In the current test, at least 0.6 gigabits were achieved - within seconds the data overcame almost 36, 000 kilometers.

Data constantly and promptly available

The communications satellite Alphasat I-XL, which serves as a relay, sent the received data packets via microwave link to its receiving station at the DLR in Oberpfaffenhofen. As it has a permanent connection to the ground, a quick and permanent connection of Earth observation satellites is now possible via this triangular connection. display

This is to make the storage of large amounts of data superfluous, the user can access the information faster. "This is relevant, for example, to many environmental and safety monitoring such as the European Copernicus program, " explains DLR project manager Rolf Meyer.

(ESA / DLR, 01.12.2014 - NPO)