By Jonathan Amos
Science reporter, BBC News
The Ariane 5-ECA got away from Kourou at the second attempt
The British military's Skynet 5A satellite has been launched into space from Kourou in French Guiana.
The spacecraft is part of a £3.6bn system that will deliver secure, high-bandwidth communications for UK and allied forces.
Sunday's lift-off came 24 hours after a first attempt was thwarted by a technical glitch in ground equipment.
Skynet rode atop an Ariane 5-ECA rocket, which left the ground at 1903 local time (2203 GMT).
"It was an incredibly nerve-racking but also an amazing experience to participate in the countdown and launch of an Ariane 5," said Patrick Wood, who has led the development of the Skynet spacecraft for manufacturer EADS Astrium.
"We've already received telemetry from it. In fact, we had a ground station see it just 10 minutes after separation. We've even sent commands to Skynet. It's behaving itself perfectly," he told BBC News shortly after the launch.
The British spacecraft is the first in what will eventually be a three-satellite constellation designed to allow the Army, Royal Navy and RAF to pass much more data, faster between command centres.
"Skynet's going to provide two-and-a-half times the capacity that the previous system provided, and allow the military to do things they just haven't been able to do in the past," Mr Wood explained.
Skynet 5A matches the capability of the best modern satellite platforms - on which the world depends for much of its telephone, TV, and internet traffic - but has been specially prepared for military use.
Four steerable antennas give it the ability to focus bandwidth on to particular locations where it is most needed - where British forces are engaged in operations.
Its technologies have also been designed to resist any interference - attempts to disable or take control of the spacecraft - and any efforts to eavesdrop on sensitive communications.
An advanced receive antenna allows the spacecraft to selectively listen to signals and filter out attempts to "jam" it.
"As far as we know, this is the most sophisticated technology of its type - certainly in Europe," said Mr Wood. "It allows you to produce peaks of reception across the surface of the Earth, and to change that antenna pattern in extremely rapid time."
Skynet 5 replaces Skynet 4. The new spacecraft system is bigger and much more powerful. The high traffic rates are in both directions.
Analysts talk increasingly of the military's "network enabled capability" - the idea that information and fast access to it are paramount.
Naval vessels have been re-equipped to use Skynet 5
"Modern warfare is all about information," said Bill Sweetman, the technology and aerospace editor for Jane's Information Group. "Every piece of satellite bandwidth is valuable and the military is always hungry for more.
"The practice is to offload mundane traffic on to commercial satellites and then to use a complementary, secure proprietary system for the traffic that has to be protected.
"Take for example the capability of unmanned air vehicles. These generate a lot of imagery and that has to be passed over a secure communications link. Modern warfare involves passing around a lot of data, and that puts a premium on satellite capacity."
The whole Skynet 5 constellation has been funded through the largest Private Finance Initiative (PFI) signed by the Ministry of Defence (MoD). The MoD does not own the hardware; it merely buys the services run over it.
Initially agreed in 2003, the PFI saw Paradigm Secure Communications, which is a subsidiary of EADS Astrium, take over and operate the UK's military satellite coms network.
As part of this £2.6bn deal, Paradigm agreed to loft new and more advanced spacecraft, and overhaul the ground systems needed to support them. This has included replacing and updating control centres, and major antennas and terminals on military ships, land vehicles and planes.
UK forces have seen a steady upgrade in all their coms systems
Paradigm gets an annual fee for providing this service. It can also earn money by selling excess bandwidth - expected to be about 50% on each spacecraft - to Nato and other friendly countries.
The cost to the British taxpayer of the PFI jumped by several hundred million pounds in 2005, principally because of a decision to go for the "physical assurance" of building a spare spacecraft rather than a straightforward insurance policy that would pay out in the event of a launch failure or breakdown in orbit.
Even so, the MoD says, the Paradigm contract should save many millions of pounds over the 18 years of the deal, compared with a more conventional procurement arrangement.
Skynet 5A was released from the Ariane 5 rocket some 30 minutes into Sunday's flight. It will take about a week for the satellite to achieve its final geostationary orbit.
The 5B platform will be launched towards the end of this year, with 5C due in orbit in 2008.
Skynet 5A's co-passenger on the rocket - the Indian TV satellite Insat 4B - also made it into orbit successfully.
THE SKYNET 5 MILITARY SATELLITE COMMUNICATIONS SYSTEM
The satellites are 'hardened' against interference. A special receive antenna (1) can resist attempts at jamming
Each spacecraft has four steerable antennas (2) that can concentrate bandwidth on to particular regions
The system gives global coverage (3), providing 2.5 times the capacity afforded by the previous system
Each spacecraft (4) is a 3x4x4.5m box and weighs just under 5 tonnes; the solar wings once unfurled measure 34m tip to tip
Improved technologies, including a solar 'sail' (5), lengthen the platforms' operational lives to at least 15 years