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The MoD has given a more-than £500m contract to Airbus UK to build and launch a new military satellite.

The spacecraft will slot into the existing constellation of secure communications platforms called Skynet, which has gone through five iterations since its inception in 1969.

Skynet-6A is due for launch in 2025.

It represents something of a gap-filler while the MoD seeks to put in place a new, long-term communications capability for British forces.

This major overhaul will affect how troops on the ground, fighters in the air, and ships at sea stay in contact with each other and their command structures.

Airbus runs the current satellite communications service under a Private Finance Initiative it signed with the ministry in 2003. This PFI included the provision of four series-5 spacecraft (A, B, C and D), the first of which has now reached an age where its performance might be expected to degrade.

", had a predicted end point to its design and fuel life and now needs replacing. It's essential therefore that we get another satellite up there to ensure continuous service," Richard Franklin, the Airbus Defence and Space UK managing director, told ����ý News.

6A will match the very best modern telecommunications satellites - on which the world depends for much of its telephone, TV, and internet traffic - but will be specially prepared for military use. This means its systems will have to be "hardened" to resist any attempts to disable or take control of them, or to eavesdrop on the sensitive traffic passing through the satellite.

Weighing about 5-6 tonnes, 6A will be an all-electric spacecraft; that is, it will rely on ion thrusters to achieve and maintain its orbit after launch.

The satellite will be built at the Airbus factories in Stevenage and Portsmouth, and tested in the new, giant thermal-vacuum chamber that's just been installed at the Rutherford Appleton Laboratory in Oxfordshire.

The contract demands Airbus also organise the rocket that will put the satellite in a geostationary orbit some 36,000km above the equator.

Under the terms of its PFI, Airbus owns and operates the existing Skynet satellites, and sells a complete communications service to the MoD.

Skynet-6A, however, marks a movement away from this model. The ministry will retain ownership of the satellite. Who gets to operate it long-term in orbit is now the topic of supreme importance to the British space sector.

The Airbus PFI comes to an end in August 2022, and the MoD has initiated a competition to find the next service provider, a programme that's been dubbed the Skynet 6 Service Delivery Wrap. Four consortia are vying for this role. The four groups are led by Airbus, Babcock, BT and Serco.

These companies also have their eye on an even bigger prize - a programme of provision the ministry is calling Enduring Capability, which will take British forces' communications infrastructure into the 2040s.

This amounts to a full modernisation project that will be worth billions to UK industry.

"For UK space, this could not be more important," said Mr Franklin. "It will support literally thousands of jobs, not just in large companies like Airbus but in a huge supply chain that includes hundreds of SMEs."

Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: