Proton rocket in return to flight

Proton rocket in return to flight

A Russian Proton rocket has launched on a mission to orbit one of the biggest commercial satellites ever built.

The Proton is carrying the six-tonne Inmarsat-4 (I4-F3) telecommunications spacecraft on a flight that will last just over nine hours.

This is the rocket's first outing since an upper-stage failure in March left a US satellite at a useless altitude.

The vehicle, operated by International Launch Services, left the Baikonur Cosmodrome in Kazakhstan at 2243 GMT.

The spacecraft's owner, the UK-based Inmarsat company, says it is confident the Proton 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.


Historically, the Proton has a fine record


It will be early on Tuesday morning, London time, before the rocket launch can be declared a success.

This is the third I4 platform to go into orbit. It is intended to 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-F3 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, but it has a much deeper governmental heritage going back to the 1960s.


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.

Although the Proton can be regarded as one of the most successful heavy boosters in history, it has experienced difficulties in recent times, with three mission failures in as many years.

The Inmarsat mission lasts nine hours and three minutes from lift-off to spacecraft separation. The rocket's Breeze M upper-stage has a flight profile that requires it to make five burns to get the I4-F3 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."


The I4 is one of the biggest commercial platforms in operation today