The U.S. Navy's new satellite to provide more agile communications for forces on the move has successfully maneuvered itself into a perch 22,300 miles above Earth and unfurled its giant umbrella-like mesh antennas.

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When the largest and most powerful Atlas rocket in history thundered to space Friday, three onboard video cameras captured the stunning views of what it's like to ride the vehicle off the launch pad and into orbit.

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Like erecting a cellular telephone tower 22,300 miles tall, the U.S. Navy's first-of-its-kind mobile communications satellite rose high above Earth last night to provide 3G voice, data and video services to military troops on the move.

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Our gallery of launch photos from the Complex 41 pad.

Our gallery of launch photos from Playalinda Beach.

The next Atlas launch is scheduled for April 27 from Cape Canaveral to deploy another spacecraft for the U.S. military's communications satellite programs -- the Air Force's second Advanced Extremely High Frequency craft to provide highly secure, jam resistant links between the president and military leaders. A two-hour launch window will open at 3:08 p.m. EDT (1908 GMT).

"ULA is honored to serve with our mission partners in the preparation and launch of this important mission for the U.S. Navy and for our U.S. Air Force customer," said Jim Sponnick, ULA vice president for mission operations. "This integrated team is singularly focused on ensuring that these critical MUOS satellites are safely delivered, providing vital communications capability to the women and men protecting our freedom around the world."

T+plus 3 hours, 1 minute, 41 seconds. SPACECRAFT SEPARATION! The Centaur upper stage, marking its milestone 200th mission, has deployed the U.S. Navy's first Mobile User Objective System satellite, dubbed MUOS 1, for a 15-year mission to provide mobile communications to U.S. and allied military forces on the move.

T+plus 3 hours, 1 minute, 30 seconds. Spin up of the Centaur has begun.

T+plus 2 hours, 59 minutes, 30 seconds. The third burn was a full success, putting Centaur exactly where it's supposed to be, with a high point of 19,323 nautical miles, a low point of 1,869 nautical miles and inclination of 19 degrees.

T+plus 2 hours, 59 minutes. Centaur is turning itself to the proper orientation for releasing the payload.

T+plus 2 hours, 58 minutes, 2 seconds. MECO 3. Main engine cutoff confirmed. Centaur has completed the powered phase of flight for the launch of MUOS 1.

T+plus 2 hours, 57 minutes, 30 seconds. The engine is burning well. This is a planned 54-second firing by the Centaur's single Pratt & Whitney Rocketdyne RL10 engine.

T+plus 2 hours, 57 minutes, 10 seconds. Ignition and full thrust! The Centaur's main engine has re-ignited for a third time in this launch sequence to accelerate the payload into the planned deployment orbit.

T+plus 2 hours, 56 minutes, 20 seconds. Cryo system prestarts are underway.

T+plus 2 hours, 55 minutes, 30 seconds. The vehicle is getting pressurized again for ignition.

T+plus 2 hours, 54 minutes, 30 seconds. Centaur has reached the desired orientation for the upcoming burn.

T+plus 2 hours, 53 minutes. Centaur uses its settling thrusters in preparation for the burn and also de-spinning from the roll.

T+plus 2 hours, 50 minutes. The rocket is performing a turn to get into the proper position for the upcoming engine burn.

T+plus 2 hours, 38 minutes. Centaur remains in good shape and in the correct orientation as it slowly rolls for passive thermal control in this parking orbit.

T+plus 2 hours, 30 minutes. Just about 30 minutes from Centaur delivering the final orbital boost and casting MUOS free to fly on its own.

From its eventual spot in geosynchronous orbit, matching Earth's rotation to hover in a parking spot 22,300 miles up, the expansive footprint of MUOS 1 will cover a huge swath of the planet to serve ships, submarines, aircraft, land vehicles and terminals in the hands of troops.

Initial testing of the craft will be performed later this spring over the mid-Pacific Ocean in view of a Hawaiian ground station. However, the final operational position in space and what geographical area of the globe the craft will cover hasn't been chosen yet.

T+plus 2 hours, 20 minutes. Bus and battery voltages, tank pressures and other system measurements look good as a healthy Centaur orbits in space on its 200th mission. Altitude now over 12,000 nautical miles.

T+plus 2 hours, 15 minutes. In its launch configuration atop the Atlas rocket with the two power-generating solar arrays stowed on the sides and the umbrella reflectors folded up, MUOS stands 22 feet tall, 12 feet wide and 6 feet deep. The craft was built on Lockheed Martin's A2100 satellite design used by dozens of previous communications spacecraft.

T+plus 2 hours, 5 minutes. Check out Spaceflight Now's Facebook page for some pictures of tonight's launch.

T+plus 2 hours. A typical Atlas 5 ascent to geosynchronous transfer orbit, the standard dropoff point for communications satellites, uses just two firings by the Centaur to achieve the highly elliptical, egg-shaped orbit to deploy the payloads. From there, the satellites use their own engines in the subsequent days to fly into the operational locations 22,300 miles above the equator.

But the sizable MUOS drove planners to create a three-burn launch profile for the hefty payload to use all of the available performance from the Atlas-Centaur that in turns saves the satellite's precious onboard fuel supply for maneuvering over its 15-year life.

"The MUOS 1 mission represents an excellent example of the performance and mission design capabilities of the Centaur," said Jim Sponnick, United Launch Alliance's vice president of mission operations. "Our customers for this mission asked for a mission design that would launch this very heavy and capable satellite in a manner that would minimize the amount of energy (and propellant) that the satellite would have to consume to position itself into the final geosynchronous orbit. Considering all of the commodities and capabilities of the Centaur, our mission design team developed this three-burn mission profile to provide an optimal solution for the MUOS customer."

The three burns provides 1,000 pounds greater lift capability than a conventional 2-burn geosynchronous transfer orbit, Sponnick said.

T+plus 114 minutes. The rocket is surpassing 10,000 nautical miles in altitude over the Indian Ocean. All systems still look good.

T+plus 100 minutes. Centaur data readings remain normal for the coast period at altitude of 8,800 nautical miles.

T+plus 90 minutes. To recap, the Atlas 5 rocket carrying the Navy's MUOS 1 next-generation mobile communications satellite launched from Cape Canaveral's Complex 41 at 5:15 p.m. EST into a beautifully clear blue Florida sky.

All appeared to go smoothly during the ascent and no problems were reported by the telemetry folks during the climb to orbit. The Centaur has performed two of its three planned firings to haul the payload to the desired perch in space. Deployment is coming at 8:16 p.m. EST.

T+plus 75 minutes. The rocket is now coasting toward a point about 15,000 nautical miles above the Indian Ocean where the third and final burn is planned at T+plus 2 hours and 57 minutes. Its current altitude is 6,000 miles.

T+plus 67 minutes. A roll reversal has been completed in this passive thermal conditioning of Centaur.

T+plus 60 minutes. The venerable U.S. upper stage rocket -- the Centaur -- that created the pathway to the Moon and every planet across the solar system is making its 200th flight tonight in a milestone mission to boost the U.S. Navy's sophisticated new mobile communications satellite to orbit.

Read our feature story about this landmark moment for Centaur.

T+plus 52 minutes. Now passing through an altitude of 3,000 nautical miles over the Central Indian Ocean.

T+plus 41 minutes. Centaur is in a slow 1.3-degree roll to keep thermal heating even across the rocket's surfaces.

T+plus 38 minutes. The vehicle just flew high above Madagascar.

T+plus 35 minutes. Centaur power bus and battery voltages are normal, tank pressures are stable as all systems continue to operate properly.

T+plus 30 minutes. Centaur now begins a quiet two-and-a-half-hour coast through space, moving higher and away from the planet before the third and final burn occurs nearly 2 hours and 57 minutes into flight. Deployment of MUOS 1 from the rocket to complete the launch is expected 3 hours, 1 minute, 23 seconds after launch.

T+plus 28 minutes. That second burn by Centaur inserted the rocket into another precise orbit as targeted, with a high point of 18,600 nautical miles, a low point of 104 nautical miles and inclination of 26 degrees.

T+plus 26 minutes, 54 seconds. MECO 2. Main engine cutoff confirmed. Centaur has completed its second burn of the day, this one taking the next step upwards to substantially increase the altitude from the previous parking to nearly geosynchronous height.

T+plus 25 minutes, 5 seconds. Engine performance remains normal.

T+plus 24 minutes, 55 seconds. About two minutes are left in the burn to reach the next orbit.

T+plus 23 minutes, 45 seconds. Continued good engine operation is being delivered by the RL10.

T+plus 22 minutes, 45 seconds. The rocket is 104 miles in altitude, some 5,189 miles downrange and traveling at 18,996 mph.

T+plus 21 minutes, 30 seconds. The engine is burning well. This is a planned six-minute firing by the Centaur's single Pratt & Whitney Rocketdyne RL10 engine.

T+plus 20 minutes, 53 seconds. Ignition! The Centaur's single RL10 engine has re-ignited to climb into a highly elliptical intermediate orbit on the way to the final perch later tonight.

T+plus 20 minutes, 42 seconds. Liquid hydrogen and liquid oxygen system prestarts are underway.

T+plus 20 minutes, 11 seconds. Centaur getting into its pressurization sequence.

T+plus 19 minutes. The flight path is taking the vehicle over the equatorial Atlantic Ocean, soon to near the western coast of Africa where the next Centaur burn will occur. It will soar away from the Indian Ocean over the course of the next couple hours before the RL10 restarts for a final time to accelerate MUOS into the geosynchronous transfer orbit and separating the payload. Here's the planned track map.

T+plus 18 minutes. Centaur's onboard systems are stable in this coast period continues.

T+plus 17 minutes. Centaur is half-way through this coast period. It is in a slow roll to keep thermal heating even across the rocket's surfaces.

T+plus 14 minutes. That first burn by Centaur inserted the rocket into the precise target orbit as planned, with a high point of 337 nautical miles, a low point of 90 nautical miles and inclination of 28.3 degrees.

T+plus 12 minutes, 22 seconds. MECO 1. Centaur's main engine has shut down following its first burn today, achieving a preliminary orbit around Earth. The rocket will coast in this orbit for about 8 minutes before the RL10 engine re-ignites for the next burn.

T+plus 11 minutes, 45 seconds. RL10 engine parameters still look good.

T+plus 11 minutes, 30 seconds. About one minute are left in this burn of Centaur.

T+plus 10 minutes, 45 seconds. The rocket is 143 miles in altitude, some 1,900 miles downrange and traveling at 15,567 mph.

T+plus 10 minutes, 15 seconds. All systems reported stable as the Centaur fires to reach an initial Earth orbit.

T+plus 9 minutes, 50 seconds. The RL10 continues to perform well, burning liquid hydrogen and liquid oxygen propellants.

T+plus 8 minutes, 15 seconds. The rocket is performing a planned roll to improve antenna links with NASA's orbiting Tracking and Data Relay Satellite System.

T+plus 7 minutes, 55 seconds. The rocket is 146 miles in altitude, some 1,147 miles downrange and traveling at 14,910 mph.

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

T+plus 6 minutes, 40 seconds. The rocket is 136 miles in altitude and traveling at 14,373 mph.

T+plus 5 minutes, 25 seconds. The rocket is 117 miles in altitude, some 560 miles downrange and traveling at 13,882 mph.

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

T+plus 4 minutes, 45 seconds. Centaur has ignited! The RL10 engine is up and running at full thrust for its first of three firings tonight to reach the intended geosynchronous transfer orbit.

T+plus 4 minutes, 34 seconds. The Atlas 5's Common Core Booster first stage has been jettisoned, and the Centaur upper stage's liquid hydrogen and liquid oxygen systems are being readied for engine start.

T+plus 4 minutes, 27 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, 35 seconds. The two-halves of the Atlas 5 rocket nose cone encapsulating the MUOS spacecraft have separated, exposed the satellite to space. Also jettisoned was the Forward Load Reactor, a two-piece deck that rings the Centaur stage to support the bulbous fairing during launch.

T+plus 3 minutes, 10 seconds. Atlas is passing an altitude of 63 miles, 131 miles east of the launch pad, traveling at 7,284 mph.

T+plus 3 minutes, 15 seconds. The RD-180 main engine continues to fire normally, burning a mixture of highly refined kerosene and liquid oxygen.

T+plus 2 minutes, 50 seconds. Reaction control system has been activated.

T+plus 2 minutes, 30 seconds. Everything still looking good on the first stage as the rocket powers downrange on the thrust being produced by the main engine.

T+plus 1 minute, 52 seconds. All five of the Aerojet-made solid rocket motors have successfully separated from the Atlas 5, having completed their job of adding a powerful kick at liftoff.

T+plus 93 seconds. Solid rocket booster burnout has occurred. But the spent motors will remain attached to the first stage for a few seconds, until the Atlas 5 reaches a point where the airborne dynamic pressure reduces to an allowable level for a safe jettison.

T+plus 60 seconds into this complex three-hour mission to deploy the Navy's first Mobile User Objective System communications satellite in a geosynchronous transfer orbit.

T+plus 50 seconds. A period of maximum dynamic pressure is being experienced by the rocket.

T+plus 45 seconds. Mach 1.

T+plus 40 seconds. The main engine is throttling down to ease the stresses on the vehicle in the lower atmosphere.

T+plus 30 seconds. The vehicle is heading due eastward to reach a 28-degree preliminary parking orbit 12 minutes from now.

T+plus 15 seconds. Pitch, yaw and roll maneuvers are underway as the Atlas 5 thunders away from Cape Canaveral with its RD-180 engine and five solid rocket boosters burning.

LIFTOFF! Liftoff of Atlas 5 with MUOS 1, beginning the U.S. Navy's new satellite system for mobile communications to military forces on the move!

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 away from launching Atlas with its heaviest payload ever and the 200th mission for the venerable Centaur upper stage.

T-minus 90 seconds. The rocket's 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 with a new mobile communications satellite for the U.S. Navy from Cape Canaveral, Florida.

The MUOS 1 spacecraft nestled inside the nose cone of the Atlas 5 rocket has switched to internal power for launch.

The ULA launch director and Air Force mission director have given their "go" to resume the countdown as schedule.

Polling of the team by Atlas launch conductor just occurred. All systems are "go" for an on-time liftoff today at 5:15 p.m. EST.

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.

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

• The 611th launch for Atlas program since 1957
• The 323rd Atlas to occur from Cape Canaveral
• The 200th mission for Centaur upper stage
• The 177th use of Centaur by an Atlas rocket
• The 29th launch of an Atlas 5 since 2002
• The 25th Atlas 5 to occur from the Cape
• The 21st Atlas 5 under United Launch Alliance
• The 8th Atlas 5 launch overseen by the Air Force
• The 9th 500-series flight of the Atlas 5
• The 3rd Atlas 5 to fly in the 551 configuration
• The 1st Atlas launch of 2012

A direct link to our text updates.

T-minus 4 minutes and holding. The countdown has entered the planned 10-minute hold to give the launch team a chance to review all systems before pressing ahead with liftoff.

The first stage liquid oxygen tank and Centaur's liquid oxygen and liquid hydrogen tanks are reported at flight level.

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

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The official forecast for today's 44-minute launch window extending from 5:15 to 5:59 p.m. EST continues to predict good weather with just some scattered clouds, good visibility, gusty but acceptable southwesterly winds and a temperature of 83 degrees. There's no weather constraints at this time and the odds of acceptable weather during the window are 90 percent.

Various versions of the Atlas rocket launched earlier constellations of U.S. Navy communications satellites, and now the family's biggest booster will begin deploying a new generation of spacecraft today.

Read our background story to learn more about the Atlas 5 rocket.

That other technical issue that came up a short time ago was looked at and deemed no violation for launch.

Thirty minutes from liftoff. The countdown clocks are heading to the T-minus 4 minute mark where a planned 10-minute hold will occur. Launch of Atlas 5 remains scheduled for 5:15 p.m. EST.

And the big topic on the previous two launch attempts was the high-altitude wind conditions. But officials report the upper level conditions are "green" right now!

The one issue has been explained by the warm temperatures being experienced today. That is no concern and that topic has been put to rest already.

Pre-launch checks of the rocket's safety system have been completed.

A couple of technical things have popped up that engineers are discussing in the normal fashion for resolution. Neither is impacting the countdown at this point as clocks continue to tick towards a 5:15 p.m. EST.

Today's liftoff begins the sophisticated MUOS system -- to be fully assembled with four more launches over the next several years -- that was created around the commercial third-generation cellular telephone architecture to substantially increase the number of users and amount of communications that can be routed to military forces.

"MUOS is a next-generation narrowband military satellite communications system that supports a worldwide, multi-service population of users in the Ultra High Frequency band. As a next-generation system, MUOS offers significantly enhanced capabilities, such as increased capacity, link availability and, for the first time, UHF (satellite-based) communications on-the-move capability," said Mark Pasquale, Lockheed Martin vice president and MUOS program manager.

"In the current (with Navy's Ultra High Frequency Follow-On satellite fleet) environment, ground users must be stationary with an antenna positioned directly toward the satellites to send out information. With MUOS, not only will users be able to connect with the satellites while on-the-move, the satellites will be connected to ground-based receiving stations that provide connectivity to the Global Information Grid, enabling users to send and receive data, calls and video worldwide.

"The system transitions from a circuit switch to an all-IP dynamic network which supports on demand, ad-hoc and priority based planning. MUOS also provides users with predetermined priority which allows bandwidth to be shared efficiently."

The liquid hydrogen tank in the Centaur upper stage just reached the 97 percent level. Topping is now beginning.

The latest briefing to mission managers shows the weather odds remain 90 percent favorable for an on-time launch of the Atlas 5 rocket today. The only noteworthy change to the forecast was bumping up the high end for expected ground winds, but they remain within the allowable limits.

Still calling for a few clouds at 3,000 feet, scattered high clouds at 30,000 feet, good visibility, southwesterly winds of 22 to 29 knots and a temperature around 83 degrees F.

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

Now 60 minutes from liftoff. Fueling of the Atlas rocket with cryogenic liquid oxygen and liquid hydrogen is proceeding as planned for a liftoff at 5:15 p.m. EST.

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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.

The first stage liquid oxygen tank is above 90 percent full now.

Passing the half-full mark on Centaur's liquid hydrogen tank.

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

First stage liquid oxygen tank is 70 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-and-a-quarter minutes of flight today. The 25,050 gallons of RP-1 were loaded into the rocket earlier.

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.

The Centaur engine chilldown sequence is being initiated.

Now just 80 minutes away from launch at 5:15 p.m. EST. No reports of any problems in the countdown and the weather looks great.

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Centaur stage liquid oxygen has reached flight level.

The first stage liquid oxygen tank has reached the 20 percent mark.

The Centaur liquid oxygen tank reached the 95 percent level. The topping off process is starting now.

The first stage liquid oxygen loading is transitioning 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 12,320 gallons of the cryogenic propellant.

Centaur liquid oxygen is three-quarters loaded.

The Centaur upper stage's liquid oxygen tank is 50 percent full.

The 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 48,745 gallons of cryogenic oxidizer for the RD-180 main engine.

Now approaching the one-third level of the Centaur's liquid oxygen tank.

The Centaur liquid oxygen tank has reached the 10 percent mark already.

Filling of the Centaur upper stage with about 4,075 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 perform three firings to propel the payload -- initially into a parking orbit, then into a highly elliptical intermediate orbit and eventually to the targeted geosynchronous transfer orbit this evening.

Now exactly two hours until launch!

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 120 minutes and counting! The launch countdown is continuing on schedule for today's flight of the Atlas 5 rocket with the MUOS 1 mobile communications satellite to serve the U.S. Defense Department.

Clocks have one more built-in hold planned at T-minus 4 minutes. That pause will last 10 minutes during which time the final "go" for launch will be given. All remains targeted for liftoff at 5:15 p.m. EST 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.

All console operators have reported GO status during the pre-fueling readiness poll. The ULA launch director also voiced his approval for moving forward with the countdown as scheduled today.

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

The ULA launch conductor at the Atlas Spaceflight Operations Center is briefing his team on procedures before entering into the final two hours of the countdown.

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T-minus 2 hours and holding. The countdown has just entered the first of two planned holds over the course of the day that will lead to the 5:15 p.m. EST launch of the Atlas rocket. This initial pause lasts 30 minutes, giving the team some margin in the countdown timeline to deal with technical issues or any work that is running behind before fueling starts. The final hold is scheduled to occur at T-minus 4 minutes and will last for 10 minutes.

The Complex 41 pad and surrounding danger area has been cleared of all workers for the remainder of the countdown.

The final hands-on work has wrapped up at the launch pad and technicians are departing the complex now as the countdown progresses smoothly this afternoon.

The latest weather update to launch managers shows the probabilities have improved to a 90 percent chance of acceptable conditions during today's launch window.

Dry air is encroaching into South and Central Florida, which is prohibiting cumulus clouds from developing this afternoon, and the chance of isolated showers has been deleted from the forecast.

For launch time, Air Force meteorologists are calling for a few low clouds at 3,000 feet, scattered high clouds at 30,000 feet, good visibility, southwesterly winds of 22 to 27 knots and a temperature around 80 degrees F.

The only slight concern is ground winds gusting higher than expected and hitting the limit in the low 30-knot range.

The guidance system testing has been reported complete.

Now entering the final three hours of the countdown to launch. Standing by for the pre-fueling weather briefing.

A single MUOS spacecraft being launched today provides more communication access than the Navy's current 8-craft Ultra High Frequency Follow-On satellite constellation combined.

"This capability is critical to the U.S. military because they depend on reliable, targeted communication to complete missions and to protect service members worldwide. MUOS is designed to support those requirements by providing users narrowband communications with greater mobility, higher data rates and improved operational availability," said Mark Pasquale, Lockheed Martin vice president and MUOS program manager.

"This capability translates into higher mission success rates and greater levels of personnel safety and awareness. MUOS is imperative in equipping warfighters with the technology they need to perform their day-to-day activities, and we are working diligently to deliver MUOS to our customer. MUOS will provide initial on-orbit capability in 2012 and will achieve full operational capability in 2015, extending UHF narrowband communications availability well past 2025."

The hazard area roadblocks around the launch site's safety perimeter are being established now. Also, the launch team has started configuring the pad's water deluge system. And a little while ago, checks of the vehicle's internal batteries were complete.

In the countdown, activities are progressing for launch just over four hours from now. Hydraulic and propulsion system preps on the Atlas first stage just finished. Also, pre-flight testing is being conducted on the C-band system used to track the rocket as it flies downrange and the S-band system for telemetry relay from vehicle.

If you are in the local Cape Canaveral area and would like to watch today's Atlas 5 rocket launch in person, check out this authoritative viewing guide on where to go.

Today's launch of the Atlas 5 rocket will be the third flight of the vehicle's 551 configuration, which is distinguished by the combination of a five-meter payload fairing, five solid rocket boosters and a single-engine Centaur upper stage, the most powerful version of the Atlas 5 currently available.

Read our full story on the 3-hour sequence to get into orbit today.

Mission managers just received a briefing from the launch weather officer, who continues to predict an 80 percent chance of favorable conditions for today's 44-minute launch window. Air Force meteorologists are calling for a few low clouds at 3,000 feet, scattered mid-level clouds at 12,000 feet, broken high clouds at 22,000 feet, a chance of isolated showers in the area, good visibility, southwesterly winds of 22 to 27 knots and a temperature around 80 degrees F.

Any violations to the various cumulus cloud rules and gusty winds pose the worries for the weather team today.

Welcome to launch day -- attempt No. 3 -- for the Atlas rocket with its heaviest payload ever, the first satellite in the U.S. Navy's newest generation of mobile communications spacecraft, and the 200th flight of the Centaur upper stage.

The countdown clocks are starting to tick right now, beginning a seven-hour sequence of work that will prepare the rocket, payload and ground systems for today's blastoff at 5:15 p.m. EST (2215 GMT).

Soon 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 C-band system used to track the rocket as it flies downrange, plus a test of the S-band telemetry relay system. The Complex 41 site will be cleared of all personnel at 2:20 p.m.

A planned half-hour hold begins at 2:35 p.m. when the count reaches T-minus 120 minutes. Near the end of the hold, the team will be polled at 3:02 p.m. to verify all is in readiness to start fueling the rocket for launch.

Supercold liquid oxygen begins flowing into the Centaur upper stage around 3:22 p.m., followed by the first stage filling around 3:35 p.m. 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 starting at 5:01 p.m. That 10-minute 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.

Today's launch window extends from 5:15 to 5:59 p.m. EST (2215-2259 GMT).

The odds acceptable launch weather conditions at Cape Canaveral today for the Atlas 5 rocket have jumped to 80 percent in the latest forecast issued by Air Force meteorologists.

"Today, Central to Eastern Florida will be in very warm, dry air ahead of a cold front that will move into the Eastern Gulf of Mexico and Northern Florida by late evening. A slight threat for shower development exists over Central Florida late in the day well ahead of the front induced by very high temperatures this afternoon. Eastern Florida should only see very isolated development if any before sunset. Strong southwesterly winds gusting into the mid to upper 20s in advance of the front are expected during the launch window. The primary concerns for launch are cumulus clouds and liftoff winds," forecasters say.

The outlook at launch time calls for a few low clouds, scattered mid-level clouds, broken high clouds, a chance of isolated showers in the area, good visibility, southwesterly winds of 22 to 27 knots and a temperature around 80 degrees F.

If the launch should slip into the weekend, the forecast is 80 percent favorable on the backup launch opportunity available Saturday during a window of 5:11 to 5:55 p.m. EST and just 40 percent on Sunday from 5:07 to 5:51 p.m. EST.

"In the event of a 24-hour delay, the cold front will slow as it moves into Southern Florida. Associated frontal clouds and strong gusty winds behind the front remain a threat for Saturday. By launch time, winds will be northerly gusting in the upper 20s/low 30s. The primary concerns for a 24-hour delay are thick clouds and liftoff winds," the latest forecast says.

"In the event of a 48-hour delay, the front in Southern Florida will begin to return northward creating cloudier conditions and an increased threat for showers over the area. By launch time on Sunday, winds will be easterly gusting into the mid to upper 20s. The primary concerns for a 48-hour delay are thick clouds, cumulus clouds and disturbed weather."

Check out today's gallery of photos showing the Atlas 5 rocket back on the launch pad again for the MUOS 1 launch.

On the pad! Aiming for a third launch attempt Friday after weather conditions spoiled back-to-back countdowns last week and a previously-scheduled classified operation occupied the Eastern Range over the past several days, an Atlas 5 rocket is again standing tall on Complex 41.

Completing the first third-of-a-mile on the trek to geosynchronous transfer orbit orbit, the Atlas 5 rocket has arrived at the pad for tomorrow's ascent with the U.S. Navy's Mobile User Objective System 1 satellite to begin constructing a new space-based constellation for global mobile communications and replacing the military's aging Ultra High Frequency (UHF) spacecraft fleet.

"Whether it's in vehicles, on ships, in submarines and aircraft, or simply carried by service members who are dismounted from vehicles and on the move, this system was designed to bring them voice and data communications," said Capt. Paul Ghyzel, program manager of the Navy's Communications Satellite Program Office.

"As we bring MUOS online, we'll bring up a capability that allows (users) to move around the battlespace and be able to continue to communicate over the horizon. The top requirements for the MUOS system have to with capacity, coverage and link availabilities. So we'll be providing 24-hour-a-day, 7-day-a-week global coverage."

The two mobile trailers connected to the launching platform, which were part of the convoy during this morning's rollout, soon will be hooked up to power and communications systems at the pad. These trailers provide conditioned air to the payload and communications with the rocket during the rollout and the countdown. They are protected from the blast of launch by a concrete structure on the north-side of the platform.

Within the next hour, the auto couplers between the pad and platform will be engaged to route umbilical connections from the ground to the rocket for tomorrow's fueling of the booster with cryogenic propellants.

Later today, the undercarriages used to move the mobile platform will be disconnected and the "trackmobiles" pulled free.

Ground crews will secure the rocket for a quiet evening leading into tomorrow's launch opportunity. Countdown clocks will start ticking seven hours before liftoff time.

The day's 44-minute launch window opens at 5:15 p.m. and closes at 5:59 p.m. EST.

Here's a timeline of the countdown's key events:

 HR:MM..Eastern...Event
T-6:20..10:15am...Countdown begins with rocket power up
T-5:30..11:05am...Weather briefing
T-4:55..11:40am...Start clearing assembly building area
T-4:20..12:15pm...C-band tracking beacon testing
T-3:40..12:55pm...S-band telemetry link checks
T-2:55...1:40pm...Establish blast danger area roadblocks
T-2:20...2:15pm...Weather briefing
T-2:15...2:20pm...Clear the pad
T-2:00...2:35pm...T-120 minutes and holding (for 30min)
T-2:00...3:00pm...Launch conductor briefing to team
T-2:00...3:02pm...Readiness poll for fueling
T-2:00...3:05pm...Resume countdown
T-1:50...3:15pm...Centaur LOX transfer line chilldown
T-1:43...3:22pm...Begin Centaur liquid oxygen loading
T-1:30...3:35pm...Begin Atlas first stage LOX loading
T-1:25...3:40pm...Centaur LH2 transfer line chilldown
T-1:10...3:55pm...Centaur RL10 engine chilldown
T-1:02...4:03pm...Begin Centaur liquid hydrogen loading
T-0:40...4:25pm...FLight termination system final test
T-0:16...4:49pm...RD-180 engine fuel fill sequence
T-0:10...4:55pm...Weather briefing
T-0:04...5:01pm...T-4 minutes and holding (for 10min)
T-0:04...5:08pm...Readiness poll for launch
T-0:04...5:11pm...Resume countdown
T-0:00...5:15pm..LAUNCH

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Now getting centered up on the pad as the platform inches along the final few feet.

The rocket has passed through the pad entrance gate on its return to Complex 41.

The United Launch Alliance Atlas 5 rocket has emerged from its vehicle assembly building for the journey to the pad, a milestone move for the vehicle's 29th trip to space.

Riding atop a mobile launching platform, the 206-foot-tall satellite booster is moving to Cape Canaveral's Complex 41 for the first of five launches to deploy the U.S. Navy's Mobile User Objective System. The Air Force is overseeing the launch operations for the Defense Department.

"On behalf of 3,600 employees, United Launch Alliance is very proud to be supporting our United States Air Force customer and also the U.S. Navy in the launch of the MUOS 1 satellite. The ULA team is singularly focused on ensuring critical satellites, such as MUOS 1, are safely delivered, providing critical communications capabilities to the women and men protecting our freedoms around the world," said Jim Sponnick, United Launch Alliance vice president for mission operations.

The rocket's rollout to the pad has begun!

This slow half-hour drive from the 30-story Vertical Integration Facility to Cape Canaveral's Complex 41 pad uses 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 two-stage rocket and the MUOS 1 spacecraft were put together inside the assembly building in preparation for this rollout event. The Atlas 5 is designed to spend minimal time at the launch pad, which does not include a service gantry like other sites.

After last week's scrubs, officials opted to move the rocket back into the VIF to shelter from the weather while waiting out the week until the next available launch slot on the Eastern Range became available.

Ready to try again after last week's disappointing weather scrubs, the Atlas 5 rocket will be hauled out to the launch pad this morning, riding the rails from its assembly building to Complex 41 for the final day-and-a-half of preparations to fly the massive new communications satellite into orbit for the Defense Department.

First motion for the rollout is targeted for 10 a.m. EST (1500 GMT).

Meanwhile, weather forecasters continue to call for a 60 percent chance of favorable conditions during Friday's launch window that opens at 5:15 p.m. EST. The possibility of cloud and wind constraints pose the concerns.

The outlook at launch time includes scattered low- and mid-level clouds, broken high clouds, a chance of isolated showers in the area, good visibility, southwesterly winds of 22 to 27 knots and a temperature around 75 degrees F.

"On launch day, a cold front will move into the Eastern Gulf of Mexico and Northern Florida providing an increased threat for showers in Central Florida by the late afternoon/evening. Strong southwesterly winds gusting into the mid to upper 20s in advance of the front are also expected during the launch window. The primary concerns for launch are thick clouds, cumulus clouds and liftoff winds," Air Force meteorologists report.

The odds are 80 percent favorable on the backup launch opportunity available Saturday during a window of 5:11 to 5:55 p.m. EST and 60 percent on Sunday from 5:07 to 5:51 p.m. EST.

"In the event of a 24-hour delay, the cold front will slow as it moves into Southern Florida. Associated frontal clouds and strong gusty winds behind the front remain a threat for Saturday. By launch time, winds will be northerly gusting in the upper 20s/low 30s. The primary concerns for a 24-hour delay are thick clouds and liftoff winds," the latest forecast says.

"In the event of a 48-hour delay, the front in Southern Florida will begin to return northward creating cloudier conditions and an increased threat for showers over the area. By launch time on Sunday, winds will be easterly gusting into the mid 20s. The primary concerns for a 48-hour delay are thick clouds and cumulus clouds."

The odds of getting some acceptable weather to launch the Atlas 5 rocket on Friday have improved to 60 percent in the latest forecast issued by Air Force meteorologists.

"On launch day, a cold front will move into the Eastern Gulf of Mexico and Northern Florida providing an increased threat for showers in Central Florida by the late afternoon/evening. Strong southwesterly winds gusting into the mid to upper 20s in advance of the front are also expected during the launch window. The primary concerns for launch are thick clouds, cumulus clouds and liftoff winds," forecasters said today.

They have removed the possibility of thunderstorms from that forecast and bumped up the chances of favorable weather from the earlier 40 percent odds.

The specifics for the 44-minute launch window call for scattered low- and mid-level clouds, a broken deck of high clouds, isolated showers in the area, 7 miles of visibility, southwesterly winds of 22 to 27 knots and a temperature of 74 degrees F.

If the launch should slip into the weekend, there's an 80 percent chance of acceptable conditions Saturday and 70 percent on Sunday.

"In the event of a 24-hour delay, the cold front will slow as it moves into Southern Florida. Associated frontal clouds and strong gusty winds behind the front remain a threat for Saturday. By launch time, winds will be northerly gusting in the upper 20s/low 30s. The primary concerns for a 24-hour delay are thick clouds and liftoff winds," the meteorologists say.

"In the event of a 48-hour delay, the front in Southern Florida will begin to return northward creating cloudier conditions and an increased threat for showers over the area. By launch time on Sunday, winds will be easterly gusting into the upper teens. The primary concerns for a 48-hour delay are thick clouds and cumulus clouds."

Managers today secured Friday as the official new launch date on the Eastern Range for the Atlas 5 rocket mission to deploy the U.S. Navy's giant new satellite to revolutionize mobile communications for warfighters.

The 44-minute launch window extends from 5:15 to 5:59 p.m. EST (2215-2259 GMT).

Rollout of the Atlas 5 from the Vertical Integration Facility to the Complex 41 pad at Cape Canaveral will occur Thursday morning, and the countdown clocks begin ticking on launch day at 10:15 a.m. EST.

Back-to-back launch attempts last week were thwarted by unfavorable high-altitude wind conditions and dismal weather brought by a passing cold front. The Eastern Range then had to reconfigure to support a previously-scheduled classified operation over the subsequent days that prevented the Atlas from trying again until this coming Friday.

The Air Force-controlled Range can handle one event at a time, providing the required tracking, safety and communications services. But the Range will be back into Atlas mode for a Friday afternoon blastoff, officials said today.

Once launched, the 206-foot-tall Atlas 5 flying its in largest, most powerful configuration to date will deploy the rocket's heaviest payload in history -- the 15,000-pound Mobile User Objective System 1 satellite, MUOS 1, to provide cellphone-like services to U.S. military forces on the move.

Weather forecasters still predict only a 40 percent chance of acceptable conditions on Friday due to concerns about anvil clouds, cumulus clouds, the thickness of clouds and gusty winds.

The outlook for Saturday is 70 percent favorable and then 80 percent "go" for Sunday.

It is looking like Friday afternoon at 5:15 p.m. EST (2215 GMT) will be the next opportunity to launch the Atlas 5 rocket carrying the U.S. Navy's next-generation mobile communications satellite.

The hoped-for Wednesday launch date was predicated on the Range becoming available quicker than expected. With that not materializing, it will be Friday before the Range can support the Atlas again.

Rollout of the mobile launch platform carrying the Atlas will occur on Thursday morning to kick off final preparations for the satellite-deployment flight. Countdown clocks begin ticking Friday at 10:15 a.m. EST.

The launch window will extend 44 minutes from 5:15 to 5:59 p.m. EST (2215-2259 GMT).

Weather forecasters, however, are predicting just a 40 percent chance of acceptable weather on Friday afternoon as another cold front slides into the local area.

"On launch day, a stronger cold front will move into Central Florida generating increasing clouds, showers and isolated thunderstorms by the afternoon. Strong southwesterly winds gusting into the low-mid 30s in advance of the front are also expected in the afternoon/evening on Friday. The primary concerns for launch are thick clouds, anvil clouds, cumulus clouds and liftoff winds," forecasters say.

The specifics call for scattered low clouds, a broken deck of mid-level clouds and overcast high clouds, rain showers and isolated storms in the area, 7 miles of visibility, southwesterly winds of 25 to 30 knots and a temperature of 73 degrees F.

If the launch should slip into the weekend, that cold front is expected to drift south of the Cape and allow the weather to improve. There's an 80 percent chance of favorable weather on both Saturday and Sunday, with only thick cloud and cumulus cloud rule concerns.


Read our earlier status center coverage.