The Russian Proton rocket aims to prove its reliability on Monday by putting into orbit one of the biggest commercial satellites ever built. Cern lab goes 'colder than space' ...
The launcher has had three failures in three years.
The most recent occurred in March and stranded a US spacecraft at a useless altitude.
International Launch Services, which flies the Proton, says an upper-stage glitch has been identified and fixed.
The launch of the six-tonne Inmarsat-4 (I4) satellite is timed for 2243 GMT.
Its flight will begin from the Baikonur cosmodrome in Kazakhstan.
The UK-based Inmarsat company says it is confident the Proton vehicle will work properly.
"We have been fully involved in the review board that they had into the last failure," an Inmarsat spokesman told BBC News.
"We have obviously ensured that the testing that went on was as comprehensive as possible; and I think it is fair to say we are very satisfied, and that things are in a good position to go for the return to flight."
This will be the third I4 platform to go into orbit. It will complete the "constellation" that Inmarsat will use over the next decade to deliver its high-speed (up to half a megabit) mobile internet and phone services to customers across the world.
The I4 is an immense telecommunications spacecraft. The main body is 7m high and incorporates a 9m-wide antenna reflector that is unfurled in space like a fan. The solar panels span 45m.
The two previous I4s were lofted by Atlas and Sea Launch vehicles.
The 58m-high, 700-tonne Proton has been launching commercial satellites since 1996, although it has a much deeper governmental heritage going back to the 1960s. Despite its recent woes, the Proton can be regarded as one of the most successful heavy boosters in history.
Protons have despatched science missions to the planets. They also launched key components of the Soviet-era Mir space station and the International Space Station.
The Inmarsat mission lasts nine hours and three minutes from lift-off to spacecraft separation. The rocket's Breeze M upper-stage will be required to make five burns to get the I4 into the correct path, taking it out to 36,000km above the planet.
The satellite will be placed over the Americas at 98 degrees West.
"We are a global operator; we always have been since our inception," the Inmarsat spokesman said.
"This launch will give us a next-generation satellite network that will be in place until the 2020s, so for our user base it is reassurance that we have a network up there that will go well into the the future."
(BBC)
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