Thursday, 15 August 2013

Alphasat : Europe's biggest ever telecommunications satellite

Europe's biggest ever telecommunications satellite has switched on its innovative British payload to begin a month of testing. Seven-metre-long Alphasat, dubbed the "A380 of space", was launched at the end of July, and is gradually being commissioned prior to entering service. The latest step was to activate its digital signal processor, the unit which will handle all the telecoms traffic passing through the platform. 

Alphasat is owned by Inmarsat PLC. The London-based company, which provides communications links for people and organisations on the move, developed the new satellite in partnership with the European and French space agencies. Alphasat will be used by broadcasters such as the shipping operators, the oil industry, the military and anyone else working away from traditional terrestrial communications networks. The spacecraft brings significant extra capability and capacity to Inmarsat's services, thanks in part to the digital processor that was developed at Astrium UK in Portsmouth.

The unit can switch bandwidth and power on to specific locations on the ground at very short notice, to meet the demand when and where it is most needed. Alphasat is the first use of the Alphabus platform developed under an Esa R&D programme. The bus allows European manufacturers to offer top end multimedia satellites to customers. Fully equipped, such satellites would weigh 8.8 tonnes at launch, and have 22kW of power. They could host as many as 230 transponders, equivalent to more than 1,000 TV channels. It will ensure Inmarsat's L-band radio-frequency allocation is used in the most efficient way possible.

"We are at the beginning of a nearly four-week test campaign for the payload," explained Franco Carnevale, Inmarsat's vice president for satellite and launch vehicles. As of [Wednesday], the payload has been switched on, part of the new and sophisticated on-board payload calibration system is up and running, the high-speed link to the advanced digital processor to set up and tear down connectivity is working and a signal has successfully been put through the forward payload, which is excellent news."

Alphasat places the spacecraft in the geostationary arc at about 8 degrees East, some 36,000km above the equator. "The brightest star in the image in the middle is Kappa Aquilae, magnitude 4.9 and close to the limit of naked-eye visibility from a very dark location," explained Mr Hopkins. "You can see the stars drifting in the image due to Earth's rotation, but the geostationary satellites are fixed. The first Meteosat Second Generation satellite is also in the frame, but as it's only 3m across it's too faint to see. The Intelsat satellite is probably of comparable brightness to Pluto," he said.

"The image was taken from Guildford, and used approximately a two-minute exposure at 200mm focal length. The field of view is about 5 degrees." Alphasat is only at 8 degrees East temporarily. Engineers plan to move it eventually to an orbital spot at 25 degrees East. From that location, it will provide coverage to Europe, the Middle East and Africa, gradually taking over the services currently delivered by a previous generation satellite, Inmarsat-4 F3.

In addition to its commercial role, Alphasat will demonstrate a number of technologies for the European Space Agency (Esa). The most noteworthy of these is a laser-based communications system which will underpin Europe's forthcoming orbital data relay system. This has been developed by German researchers to permit gigabit connections between Earth observation satellites and the ground. Alphasat will validate the laser terminal by downlinking pictures from the EU's Sentinel-1a radar spacecraft when it launches next year.

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