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ESA transfers images by laser between two satellites

FBH supplies a decisive component "“ a particularly robust pump laser module 

The ESA has announced the first gigabit transmission via laser of images between the Sentinel-1A Earth observation satellite in Low Earth Orbit (LEO) and the Alphasat communications satellite in Geostationary (GEO) orbit. During the demonstration, data transfer reached 0.6Gbps out of a possible 1.8Gps over 45,000km.

This advanced communication system based on Laser Communication Terminal (LCT) technology is a main part of the European Space Agency's (ESA) European Data Relay System (EDRS), also referred to as the SpaceDataHighway. It enables secure, high data rate communication between LEO satellites or aerial platforms and GEO satellites. The test follows one in 2008 showing the feasibility of coherent optical communication between two low earth orbiting satellites: the German satellite TerraSAR-X and the US satellite NFIRE.

The LCTs were developed by the Airbus Defence and Space subsidiary Tesat-Spacecom with the support of the German Aerospace Centre DLR. Laser modules from Ferdinand-Braun-Institut, Leibniz Institut fuer Höchstfrequenzetechnik (FBH) in Berlin also contributed to this successful test.

At the heart of each LCT on Sentinel-1A and Alphasat is a solid state Nd-doped YAG laser, which transmits light at a wavelength of 1064nm. The laser is pumped by a space-qualified laser diode bench made by FBH, a centre of excellence for III-V compound semiconductors.

The laser diode bench consists of a broad area laser diode bar with GaAsP quantum wells embedded in an AlGaAs wave guide structure emitting at 808nm with the wavelength stabilised by an external Bragg grating. According to FBH, the devices are designed to constantly operate at high reliability under harsh environment, including space irradiation and thermal and mechanical stresses.

The FBH has long-term and comprehensive experience with space applications, working with Tesat-Spacecom for over 15 years, and in projects with DLR and the ESA for many years. In optoelectronics as well as in the field of microwaves and power electronics, a variety of R&D projects deal with satellite communications. Since 2008, the newly implemented laser metrology group has worked on the development of laser modules for space-borne experiments. Meanwhile, a growing number of FBH devices from optoelectronics, microwaves, and power electronics are space-qualified. 

24/7 satellite data exchange

Thomas Mueller, head of the Electronics Business Line at Airbus Defence and Space, said: "Our laser communication technology will revolutionise earth observation and satellite communication. We are the first company which masters this new technology to open up an entirely new spectrum of communication."

According to the ESA, this recent laser link up demonstrates the potential of Europe's new space data highway to relay large volumes of data very quickly so that information from Earth-observing missions can be even more readily available. 

The ESA envisages information between satellites being exchanged 24/7. In the future, several Sentinel earth observation satellites will surround the Earth in low orbit taking a large number of pictures, which they can transmit when they pass over their ground stations in Europe or to geostationary satellites, which have their ground stations in permanent view so they can stream data to Earth all the time. 

Magali Vaissiere, ESA's Director of Telecommunications and Integrated Applications, said, "Today, space systems have become part of the global Big Data challenge. You can visualise the link of today as an optical fibre in the sky that can connect the Sentinels back home to Europe, from wherever they are on their orbit around Earth. The link is operated at 1.8 Gbit/s, with a design that could scale up to 7.2 Gbit/s in the future. Never has so much data travelled in space."

Orbiting from pole to pole, Sentinel-1A transmits data to Earth routinely, but only when it passes over its ground stations in Europe. However, geostationary satellites, have their ground stations in permanent view so they can stream data to Earth all the time.

This takes a great deal of coordination between the different teams working intensively. Later on, in routine operations, this will be fully automated.

Over the past few weeks the Sentinel-1A operations teams at ESA's European Space Operations Centre, ESOC, in Darmstadt, Germany, and ESA's Earth Observation Centre, ESRIN, in Frascati, Italy, and German Space Operations Center, GSOC, in Oberpfaffenhofen, Germany, have been working intensively to prepare for the laser link tests.

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