Satellite communications by laser could increase data rate hundredfold

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Washington, May 14 : Data exchange through satellites is usually done by radio waves, but now researchers at the Fraunhofer Institute for Laser Technology ILT in Aachen have replaced these radio signals with lasers - a technology that could increase the data rate hundredfold.

Recently Tesat-Spacecom performed a space test in which they launched two test satellites, German satellite TerraSAR-X and US satellite NFIRE, which carried a diode laser pump module developed with the help of Fraunhofer researchers.

It was found that the data between both the satellites was travelling very fast, covering more than 5000 kilometers in space without any errors and the scoring point here was that the data was being transmitted by laser.

The bandwidth achieved in the test was a hundred times greater than during conventional communication by radio waves, enabling a data rate equivalent to roughly 400 DVDs per hour.

This may enable transmitting large data packets between several satellites in the future, for instance to send image data from Earth observation satellites to a ground station. However, this has not been possible till date as the bandwidth of radio waves is not large enough.

This new form of communication is also beneficial in the sense that lasers are easier to focus than radio waves, enabling more accurately directed data transmissions.

The communication lasers on board the satellite are triggered by pump modules, which were developed to a large extent by researchers at the Fraunhofer Institute for Laser Technology ILT in Aachen.

"The modules have to withstand the vibrations and forces of acceleration on board the satellites during the launch and must then survive the inhospitable conditions in space - such as extreme radiation and strong temperature differences," said Martin Traub, who led the developments at the ILT.

He added: "We therefore tested the pump modules under extreme conditions in advance, subjecting them to temperatures of -35°C to 60°C, acceleration forces 1300 times as strong as those of the Earth, and gamma rays."

However, the modules should not be too big or too heavy for use in space: Measuring 5 x 5 x 2 centimeters, they are barely larger than a matchbox, and weigh little more than a bar of chocolate at 130 grams.

"We achieved this minimal weight by selecting the right materials and a sophisticated housing: Any material that wasn't absolutely essential was milled away," says Traub.

However, the biggest challenge in making use of lasers is that, despite the reduced weight, the heat generated by the laser's several-watt output still has to be dissipated.

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