2054 GMT (4:54 p.m. EDT)
MISSION SUCCESS! The Centaur upper stage completed its second burn and released the Global Positioning System 2F-8 satellite into the navigation network to complete today's launch of the Atlas 5 rocket.
1740 GMT (1:40 p.m. EDT)
We will pause our live updates at this time. Check back later for confirmation of the second Centaur burn and deploy of the GPS 2F-8 satellite to complete today's mission.
1738 GMT (1:38 p.m. EDT)
T+plus 17 minutes, 30 seconds. MECO 1. Centaur's main engine has shut down following its first burn today, achieving a transfer orbit to reach the GPS network around Earth. The rocket will coast in this orbit for about 3 hours before the RL10 engine re-ignites to circularize the orbit and then deploys the satellite.
1736 GMT (1:36 p.m. EDT)
T+plus 15 minutes. RL10 engine parameters still look good with two minutes left in this first of two burns during today's mission.
1735 GMT (1:35 p.m. EDT)
T+plus 14 minutes, 30 seconds. The Centaur and the GPS 2F-8 satellite are approaching orbital velocity.
1733 GMT (1:33 p.m. EDT)
T+plus 12 minutes, 20 seconds. The Centaur is accelerating at about 0.7g. Now over 2,000 miles downrange traveling at 15,500 mph.
1733 GMT (1:33 p.m. EDT)
T+plus 12 minutes. About five minutes are left in this burn of Centaur.
1732 GMT (1:32 p.m. EDT)
T+plus 11 minutes. All systems reported stable as the Centaur fires to reach an initial Earth orbit.
1730 GMT (1:30 p.m. EDT)
T+plus 9 minutes, 30 seconds. Centaur performance is reported right on target. The rocket is flying up the east coast of the United States and is 1,220 miles downrange from Cape Canaveral.
1729 GMT (1:29 p.m. EDT)
T+plus 8 minutes. The RL10 continues to perform well, burning liquid hydrogen and liquid oxygen propellants.
1728 GMT (1:28 p.m. EDT)
T+plus 7 minutes. The rocket is tracking right down the planned flight path.
1726 GMT (1:26 p.m. EDT)
T+plus 5 minutes. Centaur engine readings look good as this burn gets underway.
1725 GMT (1:25 p.m. EDT)
T+plus 4 minutes, 37 seconds. The two halves of the four-meter-diameter Atlas 5 rocket nose cone encapsulating the spacecraft have separated.
1725 GMT (1:25 p.m. EDT)
T+plus 4 minutes, 25 seconds. Centaur has ignited! The RL10 engine is up and running at full thrust to power the vehicle into orbit.
1725 GMT (1:25 p.m. EDT)
T+plus 4 minutes, 15 seconds. The Atlas 5's Common Core Booster has been jettisoned, completing the first stage of flight, and the Centaur upper stage's liquid hydrogen and liquid oxygen systems are being readied for engine start.
1725 GMT (1:25 p.m. EDT)
T+plus 4 minutes, 8 seconds. BECO. Booster Engine Cutoff is confirmed as the RD-180 powerplant on the first stage completes its burn. Standing by to fire the retro thrusters and separate the spent stage.
1724 GMT (1:24 p.m. EDT)
T+plus 3 minutes, 45 seconds. Atlas now weighs just a quarter of what it did at liftoff.
1723 GMT (1:23 p.m. EDT)
T+plus 2 minutes, 45 seconds. Reaction control system has been activated.
1723 GMT (1:23 p.m. EDT)
T+plus 2 minutes, 35 seconds. Atlas continues tracking on course.
1723 GMT (1:23 p.m. EDT)
T+plus 2 minutes, 30 seconds. Atlas now weighs half of what it did at liftoff.
1723 GMT (1:23 p.m. EDT)
T+plus 2 minutes, 15 seconds. Vehicle systems looking good.
1722 GMT (1:22 p.m. EDT)
T+plus 1 minutes, 45 seconds. The RD-180 main engine continues to fire normally, burning a mixture of highly refined kerosene and liquid oxygen.
1722 GMT (1:22 p.m. EDT)
T+plus 100 seconds. Now passing through the region of maximum aerodynamic pressure on the vehicle as its accelerates through the dense lower atmosphere.
1722 GMT (1:22 p.m. EDT)
T+plus 85 seconds. All looks good aboard Atlas as it passes Mach 1.
1722 GMT (1:22 p.m. EDT)
T+plus 60 seconds. One minute into the ascent of GPS 2F-8.
1721 GMT (1:21 p.m. EDT)
T+plus 40 seconds. The Atlas 5 is sending a thunderous roar across Florida's spaceport as it climbs into a clear sun-splashed sky over Cape Canaveral.
1721 GMT (1:21 p.m. EDT)
T+plus 15 seconds. The Atlas 5 rocket has cleared the tower on 860,000 pounds of thrust from the RD-180 main engine. Pitch, yaw and roll maneuvers are underway to put the rocket on the proper heading.
1721 GMT (1:21 p.m. EDT)
T-minus 10, 9, 8, 7, 6, 5, 4, 3, engine ignition, 1, 0 and LIFTOFF! Liftoff of the Atlas 5 rocket with a new GPS navigation satellite to serve the world. And the vehicle has cleared the tower!
1720 GMT (1:20 p.m. EDT)
T-minus 20 seconds. "Go Atlas" and "Go Centaur" was just called by launch team during a final status check.
1720 GMT (1:20 p.m. EDT)
T-minus 40 seconds. Centaur's liquid oxygen and liquid hydrogen tanks are stable at flight pressures.
1720 GMT (1:20 p.m. EDT)
T-minus 55 seconds. Range is green.
1720 GMT (1:20 p.m. EDT)
T-minus 1 minute. Now 60 seconds away from launch of the GPS 2F-8 satellite.
1719 GMT (1:19 p.m. EDT)
T-minus 90 seconds. The rocket's safety system has been armed.
1719 GMT (1:19 p.m. EDT)
T-minus 1 minute, 45 seconds. Liquid oxygen and liquid hydrogen propellant topping to the Centaur upper stage is being secured.
1719 GMT (1:19 p.m. EDT)
T-minus 1 minute, 55 seconds. The launch sequencer has been commanded to start.
1719 GMT (1:19 p.m. EDT)
T-minus 2 minutes. The Atlas first stage and Centaur upper stage are now switching from ground power to internal batteries.
1718 GMT (1:18 p.m. EDT)
T-minus 2 minutes, 30 seconds. The first stage RP-1 kerosene fuel tank and the liquid oxygen have stepped up to proper flight pressure levels.
1718 GMT (1:18 p.m. EDT)
T-minus 3 minutes. The Atlas first stage liquid oxygen replenishment is being secured so the tank can be pressurized for launch.
1717 GMT (1:17 p.m. EDT)
T-minus 3 minutes, 50 seconds. The ground pyrotechnics are enabled.
1717 GMT (1:17 p.m. EDT)
T-minus 4 minutes and counting. Clocks have resumed for the final minutes of today's countdown to launch the Atlas 5 rocket with a new spacecraft for the GPS network from Cape Canaveral, Florida.
1716 GMT (1:16 p.m. EDT)
Standing by to pick up the count.
1716 GMT (1:16 p.m. EDT)
The Boeing-built GPS 2F-8 satellites is verified configured for launch.
1715 GMT (1:15 p.m. EDT)
ULA launch director and Air Force mission director have given their respective final approvals to resume the countdown.
1715 GMT (1:15 p.m. EDT)
Polling of the team by Atlas launch conductor just occurred. All systems are "go" for a liftoff today at 1:21 p.m. EDT (1721 GMT).
1711 GMT (1:11 p.m. EDT)
Standing by for the final readiness check to be conducted. The launch team will be polled for a "go" or "no go" to proceed with the count.
1705 GMT (1:05 p.m. EDT)
All is quiet in the countdown.
1701 GMT (1:01 p.m. EDT)
Engineers are disabling the sensor responsible for the high temperature reading on the RD-180 engine. Another sensor will be monitored during the countdown to ensure the engine is ready for flight.
1656 GMT (12:56 p.m. EDT)
The launch team is studying a high temperature reading on the RD-180 engine.
1655 GMT (12:55 p.m. EDT)
The Atlas 5's payload -- the GPS 2F-8 navigation satellite -- is being transferred to internal battery power at this time.
1654 GMT (12:54 p.m. EDT)
This will be...
1651 GMT (12:51 p.m. EDT)
Just 30 minutes until liftoff time. The Atlas 5 rocket launching GPS 2F-8 is known as the 401 model. It has a common first stage with no solid rocket boosters, a cryogenic, single-engine Centaur upper stage, and a 4-meter-diameter payload shroud.

The first stage is fueled by RP-1, a highly refined kerosene, and supercold liquid oxygen. The RD-180 main engine, made by NPO Energomash, generates about 860,000 pounds of thrust. Known as the Common Core Booster, or CCB, the stage measures 42 feet in length and 10 feet diameter.

The Centaur stage features a restartable Aerojet Rocketdyne RL10A-4-2 engine burning liquid hydrogen and liquid oxygen. The total thrust is 22,300 pounds.

Protecting the payload during atmospheric ascent is the payload fairing measuring 39 feet in length and 14 feet in diameter. It is an aluminum nose cone built in two halves.

The Atlas 5 stands 189 feet tall and weighs about 745,000 pounds at liftoff.

Earlier updates