The Breeze M's main engine ignited for the fifth time to place the spacecraft in a targeted supersynchronous transfer orbit. Spacecraft separation occurred a few minutes later, and International Launch Services declared the launch a success.
The Breeze M and Inmarsat 5 F3 should now be in a transfer orbit with a low point of 295 miles, a high point of 40,416 miles, and an inclination of 50.5 degrees.
The upper stage will coast about four more hours before igniting a fifth and final time for about three-and-half minutes to inject Inmarsat 5 F3 into an egg-shaped supersynchronous transfer orbit.
Separation of the 6.7-ton Inmarsat 5 F3 satellite is scheduled for 0315 GMT (11:15 p.m. EDT).
After a two-hour coast, the Breeze M is expected to ignite its main engine again at about 1607 GMT (12:07 p.m. EDT) for another maneuver, followed by the jettison of the stage's auxiliary propellant tank, and ignition of the engine's fourth firing.
ILS says these maneuvers will occur when the Breeze M is out of communications with ground stations, so confirmation of their completion will come when antennas re-acquire signals from the rocket after the end of the fourth burn.
The Breeze M is now in a coast phase until ignition of the second upper stage burn at about 1334 GMT (9:34 a.m. EDT).
Separation of the Inmarsat 5 F2 satellite is scheduled more than 15 hours from now, after the Breeze M's fifth burn, at 0315 GMT (11:15 p.m. EDT).
This first burn should last about four-and-a-half minutes, placing the Breeze M and Inmarsat 5 F3 in a circular parking orbit 107 miles high with an inclination of 51.5 degrees.
The Inmarsat 5 F3 satellite weighs about 6,070 kilograms, or 13,382 pounds, at liftoff. Inmarsat 5 F3 was transitioned to internal power a few minutes ago.
The Proton rocket's first stage will blast off powered by six RD-276 engines producing more than 2 million pounds of thrust. The 191-foot-tall launcher will ascend northeast from Baikonur, dropping its first stage 2 minutes after liftoff, giving way to the Proton's second stage RD-0211 main engine for a three-and-a-half minute burn.
The Proton's third stage, using a RD-0213 main engine with 131,000 pounds of thrust, next will fire for about four minutes. Separation of the 13.1-foot-diameter nose cone occurs during the third stage burn at T+plus 5 minutes, 47 seconds.
The Breeze M upper stage will assume control at T+plus 9 minutes, 42 seconds, when it separates from the Proton's third stage. Five Breeze M engine burns are planned over a 15-hour period to inject the 13,382-pound Inmarsat 5 F3 spacecraft in the proper supersynchronous transfer orbit with a low point of 2,697 miles (4,341 kilometers), a high point of 40,389 miles (65,000 kilometers) and an inclination of 26.75 degrees.
Deployment of Inmarsat 5 F3 from the Breeze M upper stage is expected at 0315 GMT Saturday (11:15 p.m. EDT Friday).
The Breeze M upper stage has already been filled with its hypergolic propellant mixture, and the three-stage Proton booster will be fueled with liquid hydrazine and nitrogen tetroxide in the next few hours.
The 191-foot-tall Proton M rocket rolled to the launch pad at Baikonur on Aug. 25, riding a railroad car before it was lifted upright on the launch mount. A mobile gantry with access platforms for workers was then installed around the rocket.
The Inmarsat 5 F3 satellite owned by Inmarsat of London, a leading provider of mobile communications services, is shrouded on top of the Proton rocket.
Built by Boeing Satellite Systems, the 13,382-pound spacecraft will be positioned in geostationary orbit over the Pacific Ocean, expanding the reach of Inmarsat's next-generation Ka-band Global Xpress network.
The Russian launcher is standing on a launch pad at the Baikonur Cosmodrome in Kazakhstan counting down to liftoff at 1144 GMT (7:44 a.m. EDT) Friday, or 5:44 p.m. local time at the historic Central Asia spaceport.
The launch is the first flight of a Proton rocket since a May 16 failure that destroyed a Mexican communications satellite.
Investigators blamed a design flaw in the Proton rocket's third stage steering system brought down the May 16 launch. Engineers traced the same problem to similar Proton failures in 1988 and 2014, concluding the flaw went undetected for decades as officials attributed those mishaps to other causes.
Officials traced the problem to the Proton rocket’s third stage RD-0214 steering engine, which failed due to intense vibrations caused by an increasing imbalance in the rotor inside the engine’s turbopump.
Investigators said the material of the rotor was degraded by high temperatures, and the design of the system was misbalanced.
Roscosmos chief Igor Komarov ordered Proton-builder Khrunichev and its subcontractors to replace the rotor shaft with a unit manufactured with different materials, use different techniques to balance the rotor in the engine’s turbopump, and change the way the steering engine is attached to the frame of the third stage’s main engine.
The May 16 launch failure was the second Proton rocket to crash in a year -- and the third in two years -- and commercial orders for Proton flights have dried up.
But International Launch Services, the U.S.-based company who markets the Proton to international satellite operators, has about a half-dozen commercial missions in its backlog, beginning with Friday's launch with the third satellite for Inmarsat's new Global Xpress mobile communications network.
Communications satellite companies say the launch market needs at least three commercially viable rockets to give owners alternatives, schedule assurance and keep prices in check.
Two of the three incumbent commercial launch providers -- SpaceX and ILS -- are recovering from failures, and Arianespace lost a contract with EchoStar to launch a satellite for high-speed Internet services due to the Ariane 5 rocket's crammed manifest next year.
The EchoStar bird went to the Atlas 5 rocket, which is sold commercially by Lockheed Martin. The Atlas 5 has been a small player in the commercial launch business in recent years, primarily due to price and schedule considerations, but flight opportunities on the U.S. rocket will become more plentiful as the Pentagon completes deployment of new national security satellite fleets, which get priority in the Atlas 5 manifest.
The return of Proton, if it racks up a series of successful flights, would be welcome news to communications satellite firms around the world.
Inmarsat selected ILS to launch the three satellites needed for the Global Xpress system to provide worldwide coverage, and the London-based satellite operator purchased a fourth spacecraft as a spare.
The Global Xpress satellites are made by Boeing and each weigh about 6.7 tons with a full tank of fuel at launch.
The Inmarsat 5 F3 satellite set to go up Friday will join two identical Global Xpress birds launched by Proton in 2013 and in February 2015.
Inmarsat 5 F1 is in operational service over the Indian Ocean, the Middle East, Europe and Africa. The second satellite launched in February will enter service by the end of August over the Atlantic Ocean and the Americas.
The spacecraft set for launch Friday goes to geostationary orbit at 178 degrees east longitude to cover the Pacific Ocean region in Inmarsat's network.
With a successful launch, the $1.6 billion Global Xpress service should be operational worldwide by the end of the year, Inmarsat officials said.
The deployment is about a year late after Inmarsat grounded its launches following previous Proton failures.
"You can obviously assume that our appetite to return to flight on Proton is because we're confident they've fixed the problem from the last launch failure," said Rupert Pearce, Inmarsat's chief executive, in a conference call with investors Aug. 6. "Proton has never had a return-to- flight failure -- please everyone touch wood right now -- and we think their excellent track record there, plus our own quality assurance processes that we run across all of our own launches, gives us very high confidence that we will be up successfully."