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 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).
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.
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).
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.
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.
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.
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 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.