The main engine rumbling to life. Ice shards breaking free. The rocket lumbering off the pad. The battle against gravity being won once again. That was the scene Friday as the Atlas 5 took flight to cap a generation of Global Positioning System satellites.

Read our launch story.

“Congratulations to the ULA, Boeing and Air Force teams on the successful launch of GPS 2F-12. We began launching the 2F satellites in May 2010 and have appreciated the outstanding teamwork of everyone involved as we have worked together to deliver all 12 2F satellites. This system provides incredible capabilities to our women and men in uniform while enabling so many technologies that impact all of our daily lives. We are proud to be GPS's ride to space,” said Laura Maginnis, ULA vice president, Custom Services.

The next Atlas 5 rocket launch from Cape Canaveral is planned for March on a commercial cargo run to the International Space Station.

This was the 132nd successful Atlas program launch in a row spanning more than two decades and the 61st for an Atlas 5.

T+plus 3 hours, 23 minutes. SPACECRAFT SEPARATION! The Centaur upper stage has deployed the Global Positioning System 2F-12 satellite for the U.S. Air Force.

T+plus 3 hours, 20 minutes. The second burn by Centaur inserted the rocket into another precise orbit as targeted. The vehicle is in a circular orbit of approximately 11,000 nautical miles at 55 degrees inclination.

T+plus 3 hours, 18 minutes. MECO 2. Centaur has completed its second burn of the day. It was a planned 87-second firing to circularize the orbit.

T+plus 3 hours, 17 minutes. Ignition! The Centaur's single RL10C engine has re-ignited to finish the climb to the GPS constellation.

T+plus 3 hours, 16 minutes. Centaur pressurization sequence complete. Liquid hydrogen and liquid oxygen system prestarts now underway.

T+plus 3 hours, 12 minutes. Five minutes away from the burn. Centaur is reorienting to the proper position for the next engine firing.

T+plus 2 hours. All parameters from the Centaur are reported normal as the coast continues.

VIDEO REPLAY of today's Atlas 5 rocket launch with the GPS 2F-12.

T+plus 1 hour. The vehicle is coasting above the Indian Ocean and heading away from the Earth in this preliminary orbit.

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-12 satellite to complete today's mission.

Good performance from the vehicle has resulted in a nominal transfer orbit being achieved.

T+plus 17 minutes, 12 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 three hours before the RL10 engine re-ignites to circularize the orbit and then deploys the satellite.

T+plus 16 minutes, 10 seconds. Everything looking normal with one minute to go in this burn.

T+plus 15 minutes, 30 seconds. RL10 engine parameters still look good.

T+plus 14 minutes, 15 seconds. Now at orbital velocity. The rocket is traveling over 17,500 mph.

T+plus 13 minutes. Centaur remains on course and looking good.

T+plus 12 minutes, 15 seconds. About five minutes are left in this burn of Centaur.

T+plus 10 minutes. All systems reported stable as the Centaur fires to reach an initial Earth orbit.

T+plus 9 minutes. Centaur performance is reported right on target.

T+plus 7 minutes. The rocket is tracking right down the planned flight path.

T+plus 5 minutes. Centaur engine readings look good as this burn gets underway.

T+plus 4 minutes, 30 seconds. The two halves of the four-meter-diameter Atlas 5 rocket nose cone encapsulating the spacecraft have separated.

T+plus 4 minutes, 24 seconds. Centaur has ignited! The RL10C-1 engine is up and running at full thrust to power the vehicle into orbit.

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.

T+plus 4 minutes, 5 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.

T+plus 3 minutes, 45 seconds. Atlas now weighs just a quarter of what it did at liftoff.

T+plus 3 minutes. Atlas continues tracking on course.

T+plus 2 minutes, 45 seconds. Reaction control system has been activated.

T+plus 2 minutes, 30 seconds. Atlas now weighs half of what it did at liftoff.

T+plus 2 minutes, 15 seconds. Vehicle systems looking good.

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.

T+plus 100 seconds. Now passing through the region of maximum aerodynamic pressure on the vehicle as its accelerates through the dense lower atmosphere.

T+plus 85 seconds. All looks good aboard Atlas as it passes Mach 1.

T+plus 60 seconds. One minute into the ascent of the year's first Atlas launch.

T+plus 40 seconds. The Atlas 5 is sending a thunderous roar across Florida's spaceport. Good engine performance reported.

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.

LIFTOFF! Liftoff of the Atlas 5 rocket -- completing a generation of navigation satellite launches with GPS 2F-12.

T-minus 20 seconds. "Go Atlas" and "Go Centaur" was just called by launch team during a final status check.

T-minus 40 seconds. Centaur's liquid oxygen and liquid hydrogen tanks are stable at flight pressures.

T-minus 1 minute. Now 60 seconds from the launch of the final GPS 2 navigation satelllite.

T-minus 90 seconds. The safety system has been armed.

T-minus 1 minute, 45 seconds. Liquid oxygen and liquid hydrogen propellant topping to the Centaur upper stage is being secured.

T-minus 1 minute, 55 seconds. The launch sequencer has been commanded to start.

T-minus 2 minutes. The Atlas first stage and Centaur upper stage are now switching from ground power to internal batteries.

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.

T-minus 3 minutes. The Atlas first stage liquid oxygen replenishment is being secured so the tank can be pressurized for launch.

T-minus 3 minutes, 50 seconds. The ground pyrotechnics have been enabled.

T-minus 4 minutes and counting. Clocks have resumed for the final minutes of today's countdown to launch the Atlas 5 rocket carrying GPS 2F-12.

Countdown clocks will resume in one minute.

The GPS satellite nestled inside the nose of the Atlas 5 rocket has switched to internal power for launch.

The ULA launch director and Air Force mission director have given their permission to fly today.

Polling of the team by Atlas launch conductor has occurred. All systems are reported "go" to continue with the countdown for liftoff at 8:38 a.m. EST.

Standing by for the launch team readiness polls.

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No problems being reported by the launch team. Countdown continues to sit in the hold period at T-minus 4 minutes, waiting for the launch window to open at 8:38 a.m. EST.

Here's a look at some stats about today's mission. This will be:

• The 643rd launch for Atlas program since 1957
• The 348th Atlas launch from Cape Canaveral
• The 232nd mission of a Centaur upper stage
• The 209th use of Centaur by an Atlas rocket
• The 465th production RL10 engine to be launched
• The 10th RL10C-1 engine launched
• The 67th flight of the RD-180 main engine
• The 61st launch of an Atlas 5 since 2002
• The 24th Air Force mission for an Atlas 5
• The 91st Evolved Expendable Launch Vehicle flight
• The 104th United Launch Alliance flight overall
• The 53rd Atlas 5 under United Launch Alliance
• The 41st 400-series flight of the Atlas 5
• The 31st Atlas 5 to fly in the 401 configuration
• The 72nd GPS satellite to launch
• The 51st Boeing-built GPS satellite
• The 12th GPS Block 2F satellite
• The 17th GPS launch on an Atlas rocket
• The 6th GPS 2F on an Atlas 5
• The 1st Atlas 5 launch of 2016

Weather is going to be a real-time call with the gusty winds today for launch at 8:38amEST (1338 GMT) from Cape Canaveral. Winds are in a bit of a lull at this moment. The official odds have improved to 60 percent GO.

Thirty minutes from liftoff. This will be the 72nd GPS satellite launch since 1978, the 17th to use an Atlas rocket and the sixth Block 2F on Atlas 5.

T-minus 4 minutes and holding. The countdown has entered the planned 30-minute hold to give the launch team a chance to review all systems and assess the weather before pressing ahead with liftoff.

T-minus 5 minutes. Standing by to go into the final built-in hold.

Now 40 minutes till launch. Rumbling away from the planet on nearly a million pounds of thrust, the Atlas 5 rocket will be flying in a basic, two-stage configuration without any added strap-on solid motors. The vehicle sports an aluminum, 14-foot-diameter nose cone that encapsulates the GPS spacecraft during the atmospheric ascent before being shed.

With the liftoff thrust not considerably more than the rocket's weight, this Atlas will display a slow and majestic rise trailing only a flickering golden flame from its RD-180 main engine.

Once above the launch pad, the rocket sets sail for the trek over the Atlantic Ocean, constantly gaining speed as its double-nozzle engine gulps 25,000 gallons of kerosene fuel and 50,000 gallons of superchilled liquid oxygen in just four-and-a-half minutes.

The bronze first stage, its propellants depleted and job now completed, then jettisons with the help of tiny thrusters. Some 106.5 feet long and 12.5 feet around, the stage is discarded to fall back into the open sea.

The cryogenic Centaur upper stage ignites moments after shedding the lower booster, lighting the RL10 engine to continue clawing toward orbit.

Covered with insulating foam, this stage stretches 41.5 feet in length and 10 feet in diameter. Centaur must perform two burns to loft GPS 2F-12 into the proper orbit around the planet.

Today marks the 61st flight for Atlas 5, born of the Air Force's competition to develop next-generation Evolved Expendable Launch Vehicles. In its previous 60 missions since debuting in August 2002, the Atlas 5 has flown 23 flights dedicated to the Defense Department, 13 commercial missions, 12 for NASA and 12 with spy satellites for the National Reconnaissance Office.

The fuel-fill sequence for the first stage main engine is starting.

Fueling of the Atlas rocket with cryogenic liquid oxygen and liquid hydrogen is complete as the countdown continues as planned for a liftoff at 8:38 a.m. EST.

The liquid hydrogen tank in the Centaur upper stage just reached the 96 percent level. Topping is now beginning.

Now 60 minutes from liftoff.

Centaur's liquid hydrogen tank is 30 percent full. The cryogenic propellant will be consumed with liquid oxygen by the stage's Aerojet Rocketdyne-made RL10 engine.

Fast-filling of the first stage liquid oxygen tank has been completed. Topping mode is now underway.

The first stage liquid oxygen has reached the 80 percent level.

Chilldown of the liquid hydrogen system has been accomplished. The launch team has received the "go" to begin filling the Centaur upper stage with the supercold fuel.

Sixty percent of the Atlas liquid oxygen tank has been filled so far.

Launch of the Atlas 5 rocket is just 90 minutes away.

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And if you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.

First stage liquid oxygen tank is 40 percent full thus far. Chilled to Minus-298 degrees F, the liquid oxygen will be used with RP-1 kerosene by the RD-180 main engine on the first stage during the initial four minutes of flight today. The 25,000 gallons of RP-1 were loaded into the rocket yesterday.

Upper stage liquid oxygen has reached flight level.

The Centaur liquid oxygen tank reached the 96 percent level. The topping off process is starting now.

The first stage liquid oxygen flow rate is switching from slow-fill to fast-fill mode.

The chilldown conditioning of liquid hydrogen propellant lines at Complex 41 is starting to prepare the plumbing for transferring the Minus-423 degree F fuel into the rocket. The Centaur holds about 12,700 gallons of the cryogenic propellant.

Now three-quarters full on Centaur liquid oxygen.

Fifty percent of the Centaur liquid oxygen tank has been filled so far.

Learn more about the process United Launch Alliance uses to fuel Atlas 5 rockets.

The chilldown conditioning of the systems for the first stage liquid oxygen tank have been completed. And a "go" has been given to begin pumping supercold liquid oxygen into the Atlas 5's first stage.

The Common Core Booster stage's liquid oxygen tank is the largest tank to be filled today. It holds 49,000 gallons of cryogenic oxidizer for the RD-180 main engine.

The Centaur liquid oxygen tank has reached the 20 percent mark.

Filling of the Centaur upper stage with about 4,150 gallons of liquid oxygen has begun at Cape Canaveral's Complex 41 following the thermal conditioning of the transfer pipes.

The liquid oxygen -- chilled to Minus-298 degrees F -- will be consumed during the launch by the Centaur's single RL10 engine along with liquid hydrogen to be pumped into the stage a little later in the countdown. The Centaur will provide the thrust to put GPS 2F-12 into orbit.

The Centaur liquid oxygen pad storage area has been prepped. The next step is conditioning the transfer lines, which is now beginning to prepare the plumbing for flowing the cryogenic oxidizer.

T-minus 2 hours and counting! The launch countdown is continuing on schedule for today's flight of the Atlas 5 rocket to deploy the GPS 2F-12 satellite.

Clocks have one more built-in hold planned at T-minus 4 minutes. During that pause the final "go" for launch will be given. All remains targeted for liftoff at 8:38 a.m. EST (1338 GMT) from Cape Canaveral's Complex 41.

In the next couple of minutes, chilldown thermal conditioning of the mobile launch platform upon which the rocket stands will begin. This is meant to ease the shock on equipment when supercold cryogenic propellants start flowing into the rocket.

After briefing his team on procedures before entering into the final two hours of the countdown, the launch conductor at the Atlas Spaceflight Operations Center just held a pre-fueling readiness poll. All console operators reported a "ready" status.

The ULA launch director also voiced approval for proceeding with the countdown.

Loading of cryogenic liquid oxygen and liquid hydrogen into the Atlas 5 rocket will be getting underway a short time from now.

A reminder that if you will be away from your computer but would like to receive countdown updates, sign up for our Twitter feed to get text messages on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

T-minus 2 hours and holding. The countdown has just entered the first of two planned 30-minute holds over the course of the day that will lead to the 8:38 a.m. EST launch of the Atlas rocket. The holds give the team some margin in the countdown timeline to deal with technical issues or any work that is running behind. The final hold is scheduled to occur at T-minus 4 minutes.

A check of the current weather, the thick cloud rule is RED. Some thinning is expected and the rule should go GREEN in about an hour. The main concern for launch time is the wind.

Crews are departing the launch pad following completion of all hands-on work this morning.

The early portion of the countdown has progressed smoothly overnight. There are no issues being reported in the count and activities are on schedule.

In today's first weather briefing to mission managers, odds for the launch window now stand at 30 percent favorable as the cold front slides by. The main concern that meteorologists are watching are gusty ground winds and thick clouds.

The weather outlook calls for scattered low- and mid-level clouds, a broken high-level deck, isolated showers, good visibility, north-northwesterly winds of 24 to 28 knots and a temperature of 51 degrees F.

The Atlas-Centaur rocket has been powered up at Complex 41 and guidance system testing is getting started for today's launch, as the countdown progresses as planned.

The countdown is beginning for today’s launch of the Atlas 5 rocket to haul the Air Force’s GPS 2F-12 navigation satellite into orbit.

Clocks are picking up the seven-hour sequence of work that will prepare the booster, payload and ground systems for blastoff at 8:38 a.m. EST (1338 GMT).

The launch team will begin powering up the rocket to commence standard pre-flight tests. Over the subsequent few hours, final preps for the Centaur's liquid oxygen and liquid hydrogen systems will be performed, along with a test of the rocket's guidance system and the first stage propulsion and hydraulic preps, internal battery checks and testing of the GPS metric tracking system used to follow the rocket as it flies downrange, plus a test of the S-band telemetry relay system.

A planned hold begins when the count reaches T-minus 120 minutes. Near the end of the hold, the team will be polled to verify all is in readiness to start fueling the rocket for launch.

Supercold liquid oxygen begins flowing into the Centaur upper stage, followed by the first stage filling. Liquid hydrogen fuel loading for Centaur will be completed a short time later.

A final hold is scheduled at the T-minus 4 minute mark. That pause will give everyone a chance to finish any late work and assess the status of the rocket, payload, Range and weather before proceeding into the last moments of the countdown.

The launch window extends 19 minutes to 8:57 a.m. EST (1357 GMT).

The Global Positioning System 2F-12 satellite, the final craft built in the current manufacturing generation, and its United Launch Alliance Atlas 5 booster rocket were rolled out to pad this morning in preparation for the countdown and liftoff on Friday.

Launch is slated for 8:38 a.m. EST at the opening of a 19-minute window.

There is a 40 percent chance of acceptable weather due to a passing cold front bringing cloudy conditions and gusty ground winds.

The slow drive from the 30-story Vertical Integration Facility to the launch pad, which began at 8:01 a.m., used a pair of specially-made “trackmobiles” to carry the rocket's 1.4-million pound mobile launching platform along rail tracks for the 1,800-foot trip.

The 189-foot-tall rocket emerged from the assembly building where the vehicle's two stages and the payload were integrated over the past three weeks.

The Atlas-Centaur will launch the GPS craft directly into the navigation constellation. Deployment of the satellite occurs 3 hours and 23 minutes into flight.

"This is an exciting time for Space and Missile Systems Center. We will launch the final GPS 2F satellite culminating years of extraordinary team work and commitment to mission success," said Lt. Gen. Samuel Greaves, SMC's commander and Air Force program officer for space.

"This is a significant milestone for GPS. The GPS 2F satellite performance has been exceptional and is expected to be operational for years to come."

The rocket is flying the 401 vehicle configuration. The version features two stages and a four-meter-diameter nose cone. It is powered off the launch pad by an RD AMROSS RD-180 main engine. The Centaur upper stage is equipped with an Aerojet Rocketdyne RL10C-1.

Countdown clocks begin ticking seven hours before launch, leading to activation of the rocket, final testing and system preps.

The weather outlook calls for scattered low- and mid-level clouds, a broken high-level deck, isolated showers, good visibility, north-northwesterly winds of 24 to 28 knots and a temperature of 54 degrees F.

"For the launch count, the cold front pushes into the Space Coast late Thursday evening/early Friday morning. Showers and thunderstorms are possible during the early portions of the count with a gradual trend down late in the count. Winds become from the north-northwest and trend up overnight during the count as the pressure gradient tightens with gusts in the mid to upper-20s during the window," forecasters said this morning.

Watch this page for live updates throughout the countdown and live streaming video of the launch.

And if you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.

Launch Readiness Review this morning cleared the Atlas 5 rocket for rollout to the pad on Thursday morning and liftoff Friday morning with the GPS 2F-12 navigation satellite from Cape Canaveral.

PREVIEW: Kicking off United Launch Alliance's ambitious 2016 with as many as 15 launches planned for the U.S. military, intelligence community, NASA and commercial clients, an Atlas 5 rocket will thunder to orbit Friday to deploy the last satellite in the current generation of Global Positioning System navigation spacecraft.

Read our full story.