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Proton launches Inmarsat-5 F2

Anatoly Zak, Spaceflight Correspondent
Feb 2, 2015, 16:01 UTC

Sen—Russia's workhorse rocket opened the nation's space activities this year with a rare daylight blastoff from the frozen steppes of Kazakhstan Sunday.

A Proton-M rocket lifted off as scheduled at 12:31:00 UTC (15:31 Moscow Time, 7:31 a.m. EST) from Site 200 in Baikonur Cosmodrome. Under its payload fairing, the vehicle carried a six-ton Inmarsat-5 F2 satellite for its namesake company based in London.

The giant spacecraft built by Boeing in California will be used to provide high-speed broadband voice and data communications across the American continent and the Atlantic region. The first Inmarsat-5 satellite in the planned three-bird constellation was successfully launched by a Proton rocket in December 2013. The fourth satellite could be added to the network after 2016.

Like most communications satellites, the Inmarsat-5 family is designed to operate in the geostationary orbit 36,000 km over the equator, where spacecraft appear "hanging" in the sky to a ground observer, because its 24-hour orbital period exactly matches the Earth's rotation about its axis. However, Inmarsat-5 took a very long, though pre-planned, detour on his way to this popular destination in space. During its 15-hour, 31-minute climb, Proton's Briz-M space tug pushed the spacecraft as far as 65,000 km away from Earth, or nearly twice above its prescribed altitude.

Counter-intuitively, the exotic launch scenario actually saved the spacecraft some gas for its own thrusters, which will be needed to place it into the operational orbit and keep it there during the satellite's projected 15-year lifespan. The mass savings became possible because farther away from Earth the satellite faced less resistance from our planet's gravitational field during an energy-hungry maneuver aimed to tilt its orbit to match the Equator.

As an added benefit for the spectators on the ground, the extended flight itinerary shifted the liftoff time for the Inmarsat-5 F2 into the daylight hours in Baikonur. (Most routine Proton missions to the geostationary orbit have to take off in the depth of night, in order to catch the sunlight during prolonged phases of the ascent.) Moreover, the winter weather started clearing shortly before launch allowing the setting Sun to provide a dramatic backdrop as the Proton was thundering into the sky.

The launch of Inmarsat-5 F2 is only a beginning in a very busy flight manifest for the Russian space program, which includes at least 10 more missions for the nation's heaviest operational rocket in 2015, including the launch of the third spacecraft in the Inmarsat-5 series scheduled for the middle of the year.

In a step-by-step effort to improve the reliability of the Proton, the rocket for the Inmarsat-5 F2 mission was equipped with new angular velocity sensors, which tell the vehicle's computer brain its exact orientation in flight. New sensors replaced infamous PV-301 units, whose wrong installation in the upside down position led to a spectacular crash of a Proton in July 2013, just seconds after liftoff.