Mission success! The Inmarsat 5 F2 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.

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 F2 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 F2 into an egg-shaped supersynchronous transfer orbit.

Separation of the 6.7-ton Inmarsat 5 F2 satellite is scheduled for 0402 GMT (11:02 p.m. EST).

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 F2 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 1654 GMT (11:54 a.m. EST) 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.

T+plus 18 minutes. International Launch Services confirms the Breeze M upper stage has completed the first of four 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 1421 GMT (9:21 a.m. EST).

Separation of the Inmarsat 5 F2 satellite is scheduled more than 15 hours from now, after the Breeze M's fifth burn, at 0402 GMT (11:02 p.m. EST).

T+plus 13 minutes. Officials confirm successful shutdown of the Proton's third stage, separation of the Breeze M upper stage, and 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 F2 in a circular parking orbit 107 miles high with an inclination of 51.5 degrees.

T+plus 7 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.

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.

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.

T+plus 70 seconds. The Proton rocket has passed the speed of sound and the phase of maximum aerodynamic pressure as it heads northeast from Baikonur.

Liftoff of the Proton rocket with Inmarsat 5 F2, a 6.7-ton communications satellite to expand the reach of a new globe-spanning mobile telecom network.

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.

T-minus 2 minutes. The countdown is being run by a master computer sequencer.

T-minus 5 minutes. Inmarsat 5 F2 marks the third satellite owned by London-based Inmarsat to launch on an International Launch Services Proton rocket. It also marks the 11th satellite built by Boeing Satellite Systems to launch on an ILS Proton.

T-minus 8 minutes. The readiness of the Proton core vehicle, the Breeze M upper stage and Inmarsat 5 F2 will be verified over the next few minutes.

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 F2 satellite weighs about 6,070 kilograms, or 13,382 pounds, at liftoff. Inmarsat 5 F2 was transitioned to internal power a few minutes ago.

T-minus 11 minutes. The final launch pad workers are evacuating to a safe distance away from the rocket.

It's a frigid evening in Baikonur, with temperatures around 12 degrees Fahrenheit. Surface winds from the north-northeast and upper level winds are within limits.

With 15 minutes left in the countdown, everything remains on schedule for launch at 1231 GMT (7:31 a.m. EST; 6:31 p.m. Baikonur time). It will take more than 15 hours to deploy Inmarsat 5 F2 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 nine-hour period to inject the 13,382-pound Inmarsat 5 F2 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.

Liftoff of the Proton rocket is 30 minutes away. This will be the:

• 402nd Proton rocket launch since 1965
• 88th International Launch Services Proton since 1996
• 80th Proton M using a Breeze M upper stage since 2001
• 11th Boeing satellite launched on ILS Proton
• 3rd Inmarsat satellite launched on ILS Proton
• 1st Proton of 2015
• 1st launch from the Baikonur Cosmodrome in 2015

The launch pad gantry has moved away from the Proton rocket at Baikonur, revealing the silver booster as the countdown approaches the final hour until liftoff.

Russian officials have given approval to fuel the Proton rocket for liftoff at the Baikonur Cosmodrome in Kazakhstan at 1231 GMT (7:31 a.m. EST).

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 Jan. 29, 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 F2 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 Atlantic Ocean and the Americas, expanding the reach of Inmarsat's next-generation Ka-band Global Xpress network.

The first launch of the year for Russia's Proton rocket is scheduled for Sunday with a commercial satellite to expand Inmarsat's next-generation mobile communications network to link airplanes, marine vessels, and remote users with civilization.

The Boeing-built Inmarsat 5 F2 satellite will lift off at 1231 GMT (7:31 a.m. EST) to start a lengthy 15-hour trek to an oval-shaped transfer orbit stretching more than 40,000 miles above Earth on the way to an operational life of at least 15 years.

Fueled by hypergolic propellants, which generate thrust through chemical interaction, the Proton rocket will climb away from the Complex 200 launch site at the Baikonur Cosmodrome in Kazakhstan. Six RD-276 engines will power the 191-foot-tall rocket in the first two minutes of the flight, building up to 2.5 million pounds of thrust in vacuum.

Liftoff is expected just before sunset at Baikonur, where launch will occur at 6:31 p.m. local time.

The second stage engines will fire for nearly three-and-a-half minutes and produce 540,000 pounds of thrust. The rocket's 13.1-foot-diameter nose shroud will jettison at T+plus 5 minutes, 47 seconds, once the vehicle is above the dense lower layers of the atmosphere.

The third stage's RD-0213 engine will cut off less than 10 minutes after liftoff, then the launcher's Breeze M upper stage will take over for a complex, perfectly-timed series of five main engine firings over the next 15 hours.

The Breeze M burns will reshape Inmarsat 5 F2's orbit, aiming for a supersynchronous transfer orbit with a high point of 65,000 kilometers (40,389 miles), a low point of 4,341 kilometers (2,697 miles) and an inclination of around 26.75 degrees.

Separation of the 6.7-ton satellite is scheduled for 0402 GMT Monday (11:02 p.m. EST Sunday).

Inmarsat 5 F2 is the second satellite for the London-based company's Global Xpress mobile communications network, joining a similar craft launched by a Proton rocket in December 2013.

The third Global Xpress bird is planned for launch on a Proton mission in the second quarter of this year, and Boeing Satellites Systems is building a fourth Inmarsat 5 satellite to be ready for liftoff by late 2016.

Sunday's flight will be conducted under the auspices of International Launch Services, the U.S.-based company which sells Proton launches to commercial satellite operators.

Read our preview story for more details on the mission.