British engineers have been asked to build the payload for what will become one of the biggest commercial telecoms satellites ever launched.
The Alphasat I-XL spacecraft will probably fly in 2013
London-based Inmarsat has signed a contract with industrialists to construct the Alphasat I-XL mission.
The six-tonne satellite will deliver high-bandwidth services, such as mobile internet, to Europe, the Middle East, Asia and Africa.
It will have five times the capacity of current space platforms.
Inmarsat will use Alphasat I-XL to support its huge I-4 satellites, which deliver the company's global broadband network, BGan.
The spacecraft allow people to set up virtual offices anywhere around the world - on land or at sea. Users get half-a-megabit connections through small, laptop-sized terminals. Customers include business travellers, disaster relief workers, journalists, and people in the petrochemical and maritime industries.
The Alphasat I-XL mission has emerged from a technology programme overseen by the European and French space agencies (Esa and Cnes).
The Alphabus project was set up to develop a next-generation satellite that would allow European industry to compete at the top of the global market - especially with the products coming out of the US aerospace industry.
The Alphasat I-XL will be the first spacecraft to be lofted using the Alphabus model. In essence, Inmarsat is the first commercial customer.
In certain locations, satellite is the only means of communication
The spacecraft will incorporate an advanced new digital signal processor developed by EADS Astrium. The payload, or "brains" of the spacecraft, will be made at the company's Stevenage and Portsmouth centres.
Manufacture of the spacecraft's chassis and final assembly will take place at Astrium's other European facilities - and those of its key partner in the project, Thales Alenia Space.
"This satellite will access additional spectrum and it will be able to supply approximately five times the communications capacity of a single Inmarsat 4 satellite," said Dave Robson from Astrium.
"With advances we've made, we've been able to pack an awful lot more electronics within the existing volume. It is a technology step forward in terms of the brains of the satellite which is built in the UK."
Alphasat I-XL features a 12m aperture antenna reflector. It will have an electrical power of 12kW and a design lifetime of 15 years. The Alphabus model, though, allows for even bigger spacecraft to be made in the future, supporting missions that have a launch mass of more than eight tonnes and 18kW payload power.
These can use novel systems such as ion engines, which are more efficient than chemical thrusters in maintaining the orbit or a spacecraft over extended periods.
With their new technology and greater power, Alphabus-type missions will be able to handle more traffic at higher bandwidths.
"We believe that the new satellite will have better beam-forming capabilities and that, therefore, we should be able to put more capacity into areas; and we should be able to increase speeds," commented Inmarsat spokesman Chris McLaughlin.
"An Inmarsat BGan terminal is the size of a coffee-table book. It may well be that the Alphasat with its new processors will be able to reduce that further."
Although urbanised centres will always have superior wired communications, satellite-delivered services may be the only solution in more remote or temporary locations.
One of the world's most powerful rockets will be needed to launch a satellite of I-XL's size - something comparable to a bus or small truck. As a flagship European mission, the task of lofting Alphasat I-XL may well fall to the European bloc's premier launch vehicle, the Ariane 5 ECA. A flight is being targeted for 2013.
Inmarsat expects its investment in the satellite - excluding insurance - will be in the region of 260m euros (£190m). The Alphabus project represents an expenditure of 440m euros (£320m) by 16 Esa Member States.