Peter Schlote: Above the clouds – rapid satellite communication via laser

The fascination of space technology, the ex­­panse of outer space, and technology for in­­ternational customers – all this can be found at Tesat-Spacecom in Backnang, which is located northeast of Stuttgart and situated on the edge of Baden-Würt­­temberg’s Swabian-Franconian Forest. Anyone who has watched television via satellite can be almost sure that the picture from outer space that flickers on their screens comes from a booster unit made by Tesat-Spacecom.

Space technology made in Baden-Württemberg. Over 50 per cent of transmission electronics for television channels in outer space mounted on satellites like Astra or Eutelsat come from Tesat-Spacecom in picturesque Backnang. Since 1974, when the company was still known as AEG Telefunken, more than 500 satellites have carried Tesat-Spacecom instruments on board. Now, after more than four decades of establishing and increasing its competence in the field of information payloads for satellites, Tesat-Spacecom’s space technology products mean that it now makes the entire range of high-fre­quency (HF) products. At Tesat-Space­­com, some 1,000 employees develop, produce and sell systems and instruments for satellite communication.


Lasers: an essential tool for communications of the future. Besides developing, manufacturing and testing highly reliable instruments and assemblies, Tesat-Spacecom has since set itself another challenge: laser commu­­nications. The quantities of data that are sent through outer space are exploding.
This means that – similar to the earth-bound information networks – those fre­­quency bands available for exchanging information are becoming scarce in outer space as well. A solution to the “bandwidth crisis” is transmitting data via laser beam. For more than 30 years, engineers at Tesat-Spacecom have been occupying themselves with laser technology for use in data transmission. Since 1997, the focus has been on the development and manufacture of so-called laser commu­­ni­cation terminals (LCT).

These instruments make possible point-to-point data connections with high data volumes. The laser beam is bundled sharp­­ly and can thus transmit data over dis­­tances of 45,000 kilometres to other satellites or to earth. In such cases the lasers require a very high level of accuracy of the LCTs.

For example, it would be possible to aim such a beam at a single window on a flying jumbo jet from the earth. But not only the range but also the transmission rates are revolutionary – more than five gigabits per second have already been confirmed.

To put it figuratively, this means a trans­­fer speed that allows it to transmit the contents of a DVD within eight seconds or up to 200,000 DIN A4 pages per second. Communi­cation via laser is thus ten times faster than this was previously possible with radio waves.


The advantage of protection against elec­­tronic eavesdropping is also considerable. Due to the intensive bundling of the light beam, one would have to fly right next to a satellite in order to overhear information be­­ing ex­­changed. In addition, this special meth­­od of data transmission ensures that any spy would not recognize this data as such.

A successful acid test in outer space.The research results sound promising. The transmission of data via laser beam from the German satellite TerraSAR-X to the American satellite NFIRE was successful. TerraSAR-X is a German earth observation satellite, while NFIRE is a research satellite of the US ­Air­­force, in which various new technologies were tested in outer space for the first time. Since then, 91 Tbit – a quantity of data equivalent to more than 2,500 DVDs – have been transmitted error-free via laser beam in outer space.

To date, the exchange of data between the earth observation satellite and the data relay satellite has also been tested. Possible uses are environment or weather observa­­tions. Exact weather forecasts using better weather models, overviews of global harvests and tree populations are only a few examples of how laser technology can lead to significantly better results. But the “eye in the sky” is also valuable for monitoring ship movements or for catastrophe mon­­i­­toring services, especially when it is pos­­­sible to obtain an overview with fast trans­­mission quasi in real time.


In addition, a test is currently being car­­ried out to see whether it is also possible to send data to earth while simultaneously overcoming the atmos­­phere. An optical earth station was built specially for the purpose and at various different elevated locations, such as in Hawaii, in Andalusia and Tenerife.

Manufacturing laser terminals is ex­­pen­­­sive and complex. Twenty-two months have to be planned from the time the order is received until delivery, with at least twelve months for obtaining the parts and for manufacture. The com­­pany itself is responsible for the strategic components and the software, while mechanical and optical components are sourced from German suppliers. An LCT is not actually assembled until six months before delivery. The necessary tests under conditions re­­sembling those in outer space take three months. In a specially-constructed ther­­mo-vacuum chamber, both vacuum and temperatures between –45 °C and +65 °C are simulated. This procedure takes place in a special “clean room” atmosphere in which the air is 10,000 times cleaner than in a normal office or living room.

Future prospects. The European Space Agency ESA has rec­­ognized the potential of LCTs and has selected GMES (Global Monitoring for Environ­­ment and Security) as a crucial component in its future earth observation system.

With the new generation of earth ob­­ser­­va­­tion satellites currently being made for the ESA, the LCT is the “data network” of the information structure. Ac­­cord­ing­­ly, all data recorded by the satellites are transmitted via Tesat-Spacecom laser technology. Through the compact construction of the LCT and the low consump­­tion at very high data rates, the laser ter­­minals make possible new applications in space technology, thereby constituting a classical top product “made in Germany”.

100429_Tesat_0256_EBVThe author graduated as an electrical en­­gineer from the Hochschule für Technik und Wirtschaft des Saarlandes (Univer­sity of Applied Sciences) and graduated as Master of Science from the National Defense Uni­versity, Washington D.C. Among other things, he has been a member of the EuroMIDS in Paris and has worked for Siemens Safety Technology in Unter­schleiß­­heim and in Chessington (UK). He is CEO of Tesat-Spacecom GmbH & Co. KG.