21st October - The broadband balloon was tested for nine hours in 200km from the Arctic Circle (Image: CAPANINA)A blisteringly fast data downlink provided by a stratospheric balloon floating 24,000 metres above the Earth has been tested for the first time.

The untethered, 12,000-cubic-metre helium balloon was tested on 31 August for several hours. Analysis now shows the test was a success and sent data to the ground at 1.25 gigabits per second. That is thousands of times the capacity of a home broadband internet connection and the first time such a link has been tested from the stratosphere.

The test craft was developed by the Capanina Consortium - 14 European academic and industry partners funded mainly by the European Union. They hope the craft may be able to provide communications in disaster zones or low-cost internet access in the developing world.

David Grace, one of the project scientists behind the test, from the University of York, UK, says stratospheric communications balloons provide wireless alternatives to fixed internet infrastructure. "You could rapidly put communications infrastructure where it doesn't exist," he told New Scientist. "In developing countries it could be a cheaper way to roll out, and you could do it incrementally."

Sky-high Wi-Fi

The main concern with such floating communications hubs is ensuring they do not interfere with commercial aircraft. Controllers on the ground are able to alter the altitude of the balloon but not steer it.

The stratospheric craft was equipped with two communication systems: a high power radio antenna developed at the University of York, and an ultra-high-speed optical communications system built by the German Aerospace Centre (DRL).

The balloon's radio link was based on the 802.11b protocol. This is normally employed in Wi-Fi computer networks that extend a hundred metres or so. For the balloon test, powerful millimetre-frequency radio antennas were used, to send the signal up to 60 km. This link was used to transmit data rates of up to 11Mbits/sec.

The optical communications link developed by DRL was only tested from the balloon to the ground. It transmitted data around 100 times more rapidly. In future it should be possible to develop a bi-directional link based on this technology.

Remote tracking

Both communications systems rely on pointing a directional instrument at the balloon. "Tracking is a key issue in stratospheric broadband," says Alan Gobbi, also at the University of York. At the high altitude of the test, Gobbi says the balloon drifts about a kilometre over a few hours, depending on conditions. In the future, larger balloons could float for weeks or months at a time, providing a quick and simple communication link.

The York team used Global Positioning System (GPS) data and a modified telescope to track the balloon as it drifted. Video footage (28MB Mpeg) recorded at the test site - the Swedish Space Corporation's space centre at Esrange, 200 kilometres below the Arctic Circle - shows the University of York researchers testing the optical tracking system on the balloon.

The Capanina group is also investigating other types of high-altitude communications craft. Large airships could perhaps carry heavier communications equipment into the skies, while fleets of solar-powered aircraft could circle at high altitude for long periods.

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