By Jonathan Amos
Science reporter, BBC News
The launch of Britain's Skynet 5B spacecraft from Kourou in French Guiana has been postponed again.
5B will improve the information-carrying capability of UK forces
The flight of the sophisticated new military communications satellite was called off when a fault was detected in pipework feeding the launch pad.
It was an electronic glitch in the Ariane 5 ECA rocket itself that led to the cancellation of Friday's attempt at a launch.
The £3.6bn Skynet project represents the UK's single biggest space venture.
It will see three next-generation satellites launched into space by the middle of next year.
They will allow the Army, Royal Navy and RAF to pass much more data, faster between command centres. The bandwidth capacity of Skynet 5 is two-and-a-half times that of the existing constellation, Skynet 4.
The first new satellite, Skynet 5A, launched in March, is already making important contributions in Iraq and Afghanistan, the Ministry of Defence (MoD) says.
A spokesman for Arianespace, the company which operates Kourou, told BBC News that the anomaly occurred just prior to fuelling of the rocket. He said engineers would assess the problem before setting a new launch date and time.
Skynet 5B's co-passenger on the rocket is the Star One C1 satellite which will provide broadband services to South America.
When the Ariane does launch, it will be Skynet 5B that will be released first. Controllers expect to be able to speak to the satellite soon after separation, to begin the sequence of unpacking solar wings and antennas that are clamped for lift-off.
The satellite has been built by EADS Astrium in Stevenage and Portsmouth, and will be operated by Paradigm Secure Communications. Paradigm won a contract from the MoD to provide secure satcom services to UK forces.
The MoD buys those services and any spare bandwidth on the Skynet system can be sold to "friendly forces", earning revenue for both Paradigm and the MoD.
The Skynet Private Finance Initiative (PFI) is currently the largest City-funded defence procurement project.
"Skynet's been delivered on time and on budget," said Paradigm boss Malcolm Peto. "It's meeting the user requirements; and the MoD and the taxpayer have a chance of making money back to re-invest in other programmes because we have a 'shared gain' arrangement."