The £3.6bn system, which provides secure satellite telecommunications to British armed forces, will be boosted by the addition of a fourth spacecraft.
The first three satellites were only launched in 2007-2008, but military planners envisage even more bandwidth will be needed in the future.
Skynet 5D will be built in Portsmouth and Stevenage for a launch in 2013, most probably on an Ariane 5 rocket. Its construction will be funded by City money. The work will create 100 hi-tech jobs and secure another 800.
The Ministry of Defence does not actually own the Skynet system; it merely buys the services run over the spacecraft from a company called Paradigm Secure Communications. This arrangement - one of the most expensive Private Finance Initiatives (PFI) ever signed by the MoD - pays for itself in part by the sale of spare bandwidth to "friendly" forces.
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