0330 GMT (11:30 p.m. EDT on Fri.)
Mission success! The Inmarsat 5 F3 satellite has deployed from the Breeze M upper stage.

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.

2350 GMT (7:50 p.m. EDT)
International Launch Services confirms the completion of the Breeze M's third burn, a successful jettison of the stage's auxiliary propellant tank, and a good fourth engine burn.

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).

1530 GMT (11:30 a.m. EDT)
The Breeze M upper stage has finished the second of five burns planned for today's mission, ILS says. The nearly 18-minute burn was supposed to place the stage and Inmarsat 5 F3 in an intermediate orbit with a low point of 183 miles, a high point of 3,728 miles and an inclination of 51 degrees.

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.

1203 GMT (8:03 a.m. EDT)
T+plus 19 minutes. International Launch Services confirms the Breeze M upper stage has completed the first of five burns in this mission. The first burn was designed to accelerate the rocket and payload from a suborbital trajectory into a low-altitude parking orbit.

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).

1158 GMT (7:58 a.m. EDT)
ILS confirms a good start of the first Breeze M burn to put Inmarsat 5 F3 into a low-altitude parking orbit.
1155 GMT (7:55 a.m. EDT)
T+plus 11 minutes. Officials confirm successful shutdown of the Proton's third stage and separation of the Breeze M upper stage. We're awaiting news on the ignition of the Breeze M engine for the first of five burns on today's mission.

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.

1152 GMT (7:52 a.m. EDT)
T+plus 8 minutes. Proton's second stage has been confirmed to have separated, and the third stage RD-0213 engine has begun its burn, producing 131,000 pounds of thrust. The rocket's payload fairing has also been released now that the launcher is in the upper atmosphere.
1147 GMT (7:47 a.m. EDT)
T+plus 3 minutes, 30 seconds. The second stage's RD-0211 main engine and RD-0210 vernier engines continue firing at full power of 540,000 pounds of thrust.
1146 GMT (7:46 a.m. EDT)
T+plus 2 minutes, 25 seconds. ILS has confirmed the Proton's first stage has shut down and jettisoned, and the second stage engines are firing with a half-million pounds of thrust.
1144 GMT (7:44 a.m. EDT)
Liftoff of the Proton rocket with Inmarsat 5 F3, a 6.7-ton communications satellite to expand the reach of a new globe-spanning mobile telecom network.
1143 GMT (7:43 a.m. EDT)
T-minus 60 seconds minutes. The ignition sequence for the six first stage RD-276 engines begins at T-minus 2.5 seconds, reaching a 40 percent thrust level at T-minus 1.75 seconds and 100 percent thrust at T-minus 0.9 seconds.
1142 GMT (7:42 a.m. EDT)
T-minus 2 minutes. The countdown is being run by a master computer sequencer.
1139 GMT (7:39 a.m. EDT)
T-minus 5 minutes. Inmarsat 5 F3 marks the fourth satellite owned by London-based Inmarsat to launch on an International Launch Services Proton rocket. It also marks the 13th satellite built by Boeing Satellite Systems to launch on an ILS Proton.
1136 GMT (7:36 a.m. EDT)
T-minus 8 minutes. The readiness of the Proton core vehicle, the Breeze M upper stage and Inmarsat 5 F3 will be verified over the next few minutes.
1134 GMT (7:34 a.m. EDT)
T-minus 10 minutes. The Proton launcher on the pad weighs about 1.5 million pounds, and it will be powered into the sky by six first stage RD-276 engines producing more than 2 million pounds of thrust. It will turn to the northeast on an initial launch azimuth of 61.3 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.

1133 GMT (7:33 a.m. EDT)
T-minus 11 minutes. The final launch pad workers are evacuating to a safe distance away from the rocket.
1129 GMT (7:29 a.m. EDT)
With 15 minutes left in the countdown, everything remains on schedule for launch at 1144 GMT (7:44 a.m. EDT; 5:44 p.m. Baikonur time). It will take more than 15 hours to deploy Inmarsat 5 F3 in the proper orbit.

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).

1114 GMT (7:14 a.m. EDT)
Liftoff of the Proton rocket is 30 minutes away. This will be the:
1045 GMT (6:45 a.m. EDT)
The launch pad gantry has moved away from the Proton rocket at Baikonur, revealing the silver booster as the countdown enters the final hour until liftoff.
0730 GMT (3:30 a.m. EDT)
Russian officials have given approval to fuel the Proton rocket for liftoff at the Baikonur Cosmodrome in Kazakhstan at 1144 GMT (7:44 a.m. EDT).

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.

A critical launch from Kazakhstan on Friday aims to complete deployment of a major multibillion-dollar global communications network for London-based Inmarsat, but it carries extra importance for the Proton rocket's role in the tumultuous commercial launch business.

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."