A powerful United Launch Alliance Atlas 5 rocket roared to life Friday and launched NASA's solar-powered Juno space probe on a five-year voyage to Jupiter, the first step in a $1.1 billion mission to look for clues about the origins of the solar system in the hidden heart of its largest planet.

Read our launch story.

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The next Atlas launch is scheduled for November 25 from Cape Canaveral to send NASA's Mars Science Laboratory rover to the red planet. That rocket arrived at the Florida spaceport just last week.

"Congratulations to the entire team for successfully launching Juno on its five-year interplanetary journey to Jupiter," said Jim Sponnick, United Launch Alliance vice president for mission operations. "The ULA team is very proud to serve a critical role in delivering one-of-a-kind NASA payloads in support of the global science community and we look forward to the scientific discoveries from the Juno mission."

The three solar wings of Juno have successfully unfurled to power the spacecraft during its distant adventure to Jupiter. Telemetry shows that battery charging is underway.

Each array is 29.5 feet long and 8.7 feet wide. There's 18,698 solar cells on the panels to generate approximately 400 watts of electricity once at Jupiter.

"We are on our way, and early indications show we are on our planned trajectory," Jan Chodas, Juno project manager, said in a statement. "We will know more about Juno's status in a couple hours after its radios are energized and the signal is acquired by the Deep Space Network antennas at Canberra."

"Today, with the launch of the Juno spacecraft, NASA began a journey to yet another new frontier," NASA Administrator Charles Bolden said in a statement. "The future of exploration includes cutting-edge science like this to help us better understand our solar system and an ever-increasing array of challenging destinations."

"Flight so far looks fantastic," NASA launch director Omar Baez says. "It is in the right orbit to start its journey to Jupiter. We're right on track for that. Everything looked good."

Within minutes of separating from the rocket, Juno will establish communications with the Deep Space Network's tracking station in Canberra, Australia. Deployment of the craft's power-generating solar arrays should be getting underway shortly.

Today's official liftoff time was 12:25:00.146 p.m. EDT.

T+plus 53 minutes, 14 seconds. SPACECRAFT SEPARATION! The Centaur upper stage has deployed NASA's Juno spacecraft on its voyage to probe Jupiter's origins, interior structure, atmospheric dynamics and polar magnetosphere.

T+plus 52 minutes, 45 seconds. Spin up to 4.8 rpm has begun.

T+plus 52 minutes, 5 seconds. Centaur has turned itself to the proper orientation for releasing the payload.

T+plus 51 minutes, 25 seconds. Centaur has hit its launch performance targets.

T+plus 50 minutes, 55 seconds. Bus and battery voltages, tank pressures and other system measurements look good.

T+plus 49 minutes, 59 seconds. MECO 2. Main engine cutoff confirmed. Centaur has completed its second burn of the day, this one to give the final boost to propel Juno out of Earth orbit.

T+plus 49 minutes. Altitude now 240 nautical miles.

T+plus 48 minutes, 5 seconds. About two minutes are left in the burn to reach Juno's planned escape velocity.

T+plus 47 minutes, 15 seconds. Vehicle's current acceleration is 0.95 g's.

T+plus 46 minutes, 45 seconds. Engine performance remains normal.

T+plus 44 minutes, 45 seconds. Continued good engine operation is being delivered by the RL10.

T+plus 44 minutes. Vehicle acceleration is smooth at 0.69 g's.

T+plus 42 minutes. This burn is occurring 102 nautical miles above the Indian Ocean.

T+plus 41 minutes, 30 seconds. The engine is burning well. This is a planned nine-minute firing by the Centaur's single Pratt & Whitney Rocketdyne RL10 engine.

T+plus 40 minutes, 47 seconds. Ignition and full thrust! The Centaur's single RL10 engine has re-ignited to propel Juno into its hyperbolic departure orbit.

T+plus 40 minutes, 38 seconds. Liquid hydrogen and liquid oxygen system prestarts are underway.

T+plus 39 minutes, 45 seconds. Centaur is getting pressurized again for the next engine burn.

T+plus 39 minutes, 15 seconds. The reorientation has been accomplished.

T+plus 37 minutes. Centaur is using its settling thrusters in preparation for the burn and also de-spinning from the roll.

T+plus 33 minutes, 15 seconds. The rocket is performing its turn to the proper position for the upcoming engine burn.

T+plus 32 minutes. Now 10 minutes away from Centaur's engine restart.

T+plus 29 minutes. A roll reversal has been completed in this passive thermal conditioning of Centaur.

T+plus 26 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 24 minutes. Centaur's onboard systems are stable in this coast period continues.

T+plus 20 minutes. The flight path is taking the vehicle over the equatorial Atlantic Ocean, soon to cross Africa. It will fly over the Indian Ocean where the RL10 will restart to accelerate Juno out of Earth orbit before separating the payload above Australia. Here's the planned track map.

T+plus 16 minutes, 30 seconds. All vehicle parameters still reported normal.

T+plus 14 minutes. That first burn by Centaur inserted the rocket into an orbit with a high point of 122 nautical miles, a low point of 105 statute miles and inclination of 28.8 degrees. That's right on target.

T+plus 11 minutes, 30 seconds. The rocket is performing its turn to the proper position for the coast.

T+plus 10 minutes, 49 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 30 minutes before the RL10 engine re-ignites.

T+plus 10 minutes. RL10 engine parameters still look good.

T+plus 9 minutes, 45 seconds. About one minute are left in this burn of Centaur.

T+plus 8 minutes, 45 seconds. All systems reported stable as the Centaur fires to reach an initial Earth orbit.

T+plus 8 minutes. The RL10 continues to perform well, burning liquid hydrogen and liquid oxygen propellants.

T+plus 7 minutes, 45 seconds. Now 140 miles in altitude, 1,081 miles downrange from the launch pad, traveling at 15,339 mph.

T+plus 7 minutes, 15 seconds. The rocket has flown out of range from Florida tracking stations. Antigua Island has acquired.

T+plus 5 minutes, 45 seconds. The rocket is tracking right down the planned flight path.

T+plus 5 minutes, 35 seconds. The rocket is 112 miles in altitude, some 589 miles downrange and traveling 14,318 mph.

T+plus 5 minutes, 15 seconds. Centaur engine readings look good as this burn gets underway.

T+plus 4 minutes, 52 seconds. Centaur has ignited! The RL10 engine is up and running at full thrust for its first of two planned firings today.

T+plus 4 minutes, 40 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, 32 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, 38 seconds. The two-halves of the Atlas 5 rocket nose cone encapsulating the Juno 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, 15 seconds. The RD-180 main engine continues to fire normally, burning a mixture of highly refined kerosene and liquid oxygen.

T+plus 3 minutes. The rocket is 60 miles in altitude, some 118 miles downrange and traveling over 6,000 mph.

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

T+plus 2 minutes, 45 seconds. The rocket is 45 miles in altitude, some 69 miles downrange, traveling at 5,400 mph.

T+plus 1 minute, 48 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 1 minute, 40 seconds. The RD-180 has revved back to full throttle.

T+plus 94 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. The launcher is departing Cape Canaveral to propel Juno on its five-year trajectory to reach Jupiter.

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 15 seconds. Pitch, yaw and roll maneuvers are underway as the Atlas 5 powers into the sky with its RD-180 engine and five solid rocket boosters burning strong.

LIFTOFF! Liftoff of Juno on a 1.8-billion-mile trek to the king of planets! And the Atlas 5 rocket has cleared the tower!

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. Juno has just 60 seconds left on planet Earth before beginning its journey to Jupiter.

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 with Juno bound for Jupiter. Liftoff is set to occur at 12:25 p.m. EDT.

Countdown clocks will resume in one minute.

Juno is running on internal power and configured for launch.

The ULA launch director has given his "go" for today's liftoff.

Polling of the team by Atlas launch conductor just occurred. All technical systems are reported "go" to continue with the countdown for liftoff at 12:18 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.

The Juno spacecraft nestled inside the nose cone of the Atlas 5 rocket is switching to internal power for launch.

NASA launch director Omar Baez has polled his advisory team and given the agency's approval to proceed with the countdown.

The Range has approved the new 12:25 p.m. EDT launch time.

A reminder that today's available launch window stretches to 12:43 p.m. EDT. That's the final moment in which liftoff can occur today. But the launch team's current aim is 12:25 p.m. EDT.

NEW LAUNCH TIME has been targeted for 12:25 p.m. EDT.

The additional engineering discussion was to ensure the ground-side helium problem would create no further ramifications. But the team has determined this situation is no contraint to launching the Atlas rocket today.

HOLD EXTENDED by five more minutes. Launch time has moved to 12:18 p.m. EDT.

NASA Engineering says the team is going to need a bit more time to finish putting the technical issue to rest.

Standing by to resume the pre-flight activities that were placed in an extended hold while engineers sorted out a couple of technical issues and the Range to swept the hazard box again.

OFFICIAL NEW LAUNCH TIME has been established for 12:13 p.m. EDT.

FIVE MORE MINUTES added to the hold, delaying launch to 12:09 p.m. EDT.

The Atlas 5 rocket now stands ready for launch, pending a final OK from the Range that the hazard area is clear.

The anomaly team says the testing determined the excessive charging of the Centaur helium system is being caused by a ground-side problem. Engineers are switching the charging to a backup system, clearing the way for launch.

FURTHER HOLD ORDERED lasting five more minutes, meaning the launch time has slipped to 12:04 p.m. EDT.

RANGE NOW 'NO GO' while safety personnel sweep the hazard area off the coast of Cape Canaveral.

The Centaur helium problem appears to be on the ground-side of the system.

The earlier issue about a first stage purge pressure sensor reading has been reviewed and determined to be no concern for launch.

This upcoming test, which should take about five minutes to run, is an effort to determine if there is a leak in the helium system.

HOLD EXTENDED by 10 more minutes, putting launch no sooner than 11:59 a.m. EDT.

The team is going to stop flow to the Centaur while running some tests.

FIVE MORE MINUTES have been inserted into this countdown hold, delaying launch to 11:49 a.m. EDT.

NASA says the helium system charge cycle rate being seen today is being compared with the rate recorded during the countdown dress rehearsal a couple of weeks ago, plus looking at the ground-side of the system and performing a leak check, a spokesman says.

ANOTHER HOLD EXTENSION has been added, pushing launch time back to 11:44 a.m. EDT.

Today's launch opportunity extends to 12:43 p.m. EDT, so there's plenty of time for engineers to work through these technical issues that popped up late in the countdown.

HOLD EXTENDED by five minutes to review these technical issues. So that puts launch no sooner than 11:39 a.m. EDT.

Liftoff likely will be delayed at least a few minutes.

The Juno spacecraft's transfer to internal power will be delayed while the helium issue is assessed.

The anomaly team is starting a discussion about higher the expected cycles of Centaur helium system charges.

The launch team is looking at the momentary first stage purge pressure sensor reading. But that doesn't appear to be an issue.

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

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.

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

The official forecast for today's 69-minute launch window extending from 11:34 a.m. to 12:43 p.m. EDT continues to predict good weather with just some scattered clouds, southerly winds of 12 to 16 knots and a temperature of 88 degrees. There's no weather constraints at this time and the odds of acceptable weather during the window have improved to 80 percent. The only concern later would be cumulus clouds along the seabreeze as it develops.

Now just 20 minutes away from launch.

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

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

• The 609th launch for Atlas program since 1957
• The 321st Atlas to occur from Cape Canaveral
• The 27th launch of an Atlas 5 since 2002
• The 23rd Atlas 5 to occur from the Cape
• The 19th Atlas 5 under United Launch Alliance
• The 2nd Atlas 5 to fly in the 551 configuration
• The 5th NASA launch on Atlas 5
• The 4th Atlas launch of 2011

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

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 11:34 a.m. EDT.

Just 45 minutes until liftoff time of the Juno spacecraft destined to orbit Jupiter and unravel the mysteries of the solar system's largest planet.

Juno's journey to Jupiter is a cosmic feat requiring an exceptionally powerful rocket and a gravity slingshot delivered by Earth to cover 1.8 billion miles in five years, ultimately becoming the fastest human-made object before braking into orbit around the king of planets.

"We are sending a robot there, but really it's our eyes and our ears, we're going there," said Steve Matousek, Juno proposal manager from JPL.

"When I first started working on Juno, it blew me away that we knew so little about the biggest planet in the solar system. We don't know what the core is made out of. Why is the magnetic field so large and so powerful? How far down do the clouds go on Jupiter? Those are just some basic questions. When we flyby close on Juno and we start getting that science data back, we'll be able to answer those questions."

Following launch today aboard the most energetic version of the Atlas 5 rocket currently available to achieve a speed of about 25,000 miles per hour, Juno will be placed on a trajectory looping out past the orbit of Mars before turning back to Earth for a critical encounter that will use our home planet's gravity as a slingshot to hurl the spacecraft onward to Jupiter.

"We'll send Juno on its way on a hyperbolic departure orbit," said John Calvert, the mission manager at NASA's Launch Services Program. "It will come back and visit us again on Earth in two years and get a little trajectory boost, give it the energy it needs swing out to Jupiter's orbit."

A pair of engine firings next year -- planned for August 30 and September 3, 2012 -- will direct Juno to its Earth flyby that occurs on October 9, 2013 at an altitude of just 310 miles above the planet.

Juno will gain 16,330 miles per hour in velocity from the gravity assist, enabling the probe's flight path to reach Jupiter.

"The gravity slingshot of the Earth's gravity well to then propel us out towards Jupiter," said Jan Chodas, Juno's project manager.

At this moment, Jupiter is 445 million miles away from Earth. But the circuitous route that Juno will take stretches 1.8 billion miles from launch until arrival at its destination.

Jupiter's gravitational pull will draw Juno inward as the craft approaches, eventually reaching a speed of about 160,000 miles per hour -- making it the fastest human-made object ever -- before putting on the brakes to enter orbit.

The spacecraft gets to Jupiter on July 4, 2016, firing its main engine for 30 minutes to enter a 107-day capture orbit around the planet. Further maneuvers will narrow that orbit down to 11-day durations for the science mapping expedition.

"Jupiter orbit insertion is almost like reverse thrust in a jet when it's landing. We're going very close to Jupiter. In fact, we're moving faster than any human-made object has ever moved at the time we do this. You basically turn the spacecraft so the engines are facing forward, you fire them and they slow you down, just like the reverse thrust of a jet, except it's a rocket engine," said Scott Bolton, Juno's principal investigator. "That slows us down enough so Jupiter's gravity field now grabs us and we're trapped in orbit around Jupiter."

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

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

The weather continues to look beautiful here at Cape Canaveral.

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

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 11:34 a.m. EDT.

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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.

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.

First stage liquid oxygen tank is 50 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 25,000 gallons of RP-1 were loaded into the rocket earlier.

The Centaur engine chilldown sequence is being initiated.

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

Upper stage liquid oxygen has reached flight level.

Now just 90 minutes away from launch.

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

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

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 12,680 gallons of the cryogenic propellant.

Centaur liquid oxygen is three-quarters loaded.

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 48,860 gallons of cryogenic oxidizer for the RD-180 main engine.

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

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 4,150 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 perform two firings to propel the payload -- initially into a parking orbit and then out of Earth orbit today.

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 Juno spacecraft.

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 11:34 a.m. EDT 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 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.

NASA launch director Omar Baez has polled his advisory team and given the agency's approval to proceed with rocket fueling operations this morning.

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The latest weather update to launch managers shows things are unchanged. There's still a 70 percent chance of acceptable conditions during today's launch window. Air Force meteorologists are calling for some scattered clouds at 3,000 and 25,000 feet, possibly some isolated rain showers, good visibility, southeasterly winds of 12 to 16 knots and a temperature of 86 degrees F.

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 11:34 a.m. EDT 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. The final hold is scheduled to occur at T-minus 4 minutes and will last for 10 minutes.

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

Juno has three weeks of daily launch opportunities available through August 26 to begin its voyage away from Earth -- a period dictated by alignment of the planets. Jan Chodas, the project manager, said the window is long enough that it "gives us a 99 percent probability" of launching.

"Obviously launching anything isn't easy. Given these planetary windows, we know we don't have any room for error and we really need to take advantage of the opportunities we are given," said John Calvert, the mission manager at NASA's Launch Services Program.

"In the case of Juno, we looked at a few vehicle enhancements, kind of derived from the Pluto New Horizons mission that enable us to extend our daily opportunities. We have a minimum of a 69-minute window on the opening launch day on the 5th and we'll go up to a maximum of 90 minutes. We feel is really a good opportunity on each one of those days to be able to launch this thing successfully."

The guidance system testing has been reported complete.

The hazard area roadblocks around the launch site's safety perimeter are being established now. And the launch team has started configuring the pad's water deluge system. Also, testing is being conducted of the C-band system used to track the rocket as it flies downrange, the S-band system for telemetry relay from vehicle and the vehicle's internal batteries.

Good day from the Kennedy Space Center where it's a beautiful Florida morning for a rocket launch. We're now watching the final four hours in the countdown for today's flight of the Atlas 5 rocket and the Juno spacecraft headed for Jupiter to study the origins and evolution of our solar system's largest planet. Activities are proceeding on schedule for a liftoff at 11:34 a.m. EDT from Cape Canaveral's Complex 41.

Today's launch of the Atlas 5 rocket will be the second 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.

Depending on a payload's weight and desired orbit, mission planners add strap-on solid boosters to the United Launch Alliance-made rocket to incrementally increase the vehicle's performance.

Atlas 5 vehicles are capable of flying with as many as five boosters, an option that was employed to generate as much thrust as possible to launch NASA's New Horizons space probe bound for Pluto -- and now NASA's Juno to Jupiter.

"The 551 configuration is the most powerful in the Atlas family of rockets, and we needed every ounce of that energy to lift the maximum amount of mass to Jupiter. It's not cheap, it's not easy to get to Jupiter, so we want to make sure we get there with every ounce we can," said John Calvert, the mission manager at NASA's Launch Services Program.

The Russian RD-180 first stage main engine will ignite at T-minus 2.7 seconds, shooting a giant cloud of steam from the pad's main exhaust duct while undergoing a check to ensure its vital signs are healthy. The five strap-on solid rocket boosters are lit at T+plus 0.8 seconds, leading to liftoff at T+plus 1.1 seconds.

The combined power will send the 20-story Atlas vehicle thundering into the sky in a hurry. Its fast speed off the launch pad will be remarkably different than other Atlas 5 missions without solid boosters that appear majestically slow.

"It will be really quick because of those five solid rocket boosters burning together," said Mike Woolley of United Launch Alliance.

The Aerojet-made solid boosters will burn for about 90 seconds to assist the RD-180 in propelling the rocket. The SRB casings remain attached to the first stage for a few additional seconds before separating.

Once out of the discernible atmosphere, the bulbous nose cone encapsulating the Juno payload can be shed at T+plus 3 minutes, 25 seconds. The fairing was made by Ruag Space of Switzerland.

The kerosene-fueled first stage will continue to fire until T+plus 4 minutes, 27 seconds. The bronze stage separates about six seconds later, leaving the hydrogen-fueled Centaur upper stage to ignite for a burn lasting nearly six minutes that will inject itself into a preliminary orbit.

Centaur completes its first burn over the central Atlantic Ocean and enters a half-hour coast. The Pratt & Whitney Rocketdyne RL10 cryogenic engine then restarts for a nine-minute firing to propel the spacecraft out of Earth orbit to begin the 1.8-billion mile trek to explore Jupiter.

Juno separates from the rocket at T+plus 53 minutes, 49 seconds over Australia. The craft will establish communications with the Canberra tracking station and begin deploying its power-generating solar arrays within minutes.

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The weather outlook for today's 69-minute launch window continues to predict a 70 percent chance of being acceptable for the Atlas 5 rocket to fly. Air Force meteorologists are calling for some scattered clouds at 3,000 and 25,000 feet, possibly some isolated rain showers, good visibility, southeasterly winds of 12 to 16 knots and a temperature of 86 degrees F.

If the launch should slip to tomorrow for some reason, similar weather is expected as meteorologists once again give a 70 percent chance of acceptable conditions. The odds are 60 percent favorable on Sunday with a chance of isolated thunderstorms introduced into the forecast.

It's launch day for the Juno spacecraft aboard the Atlas 5 vehicle. The countdown clocks are starting to tick, beginning a seven-hour sequence of work that will prepare the rocket, payload and ground systems for today's blastoff.

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 8:39 a.m.

A planned half-hour hold begins at 8:54 a.m. when the count reaches T-minus 120 minutes. Near the end of the hold, the team will be polled at 9:21 a.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 9:31 a.m., followed by the first stage filling around 9:44 a.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 11:20 a.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 11:34 a.m. to 12:43 p.m. EDT (1534-1643 GMT).

Check out today's gallery of photos showing the Atlas 5 rocket being rolled to the launch pad.

The weather forecast continues to call for a 70 percent chance of favorable conditions during Friday's launch window. The possibility of cumulus cloud constraints are the only concern as the typical summertime seabreeze develops in the late morning.

The outlook at launch time includes scattered low and high clouds, isolated showers in the area, good visibility, southeasterly winds of 12 to 16 knots and a temperature around 86 degrees F.

"On launch day, Tropical Storm Emily is forecast to be in the vicinity of Eastern Cuba to Southern Bahamas as a strengthening tropical storm (40 kts gusting to 50 kts). Winds at (the launch pad) are expected from the south gusting in the low teens during the count and mid-teens through the window," Air Force meteorologists report.

If the launch should slip to Saturday for some reason, the odds of acceptable weather fall to just 30 percent as the approaching Emily brings disturbed weather and higher winds.

"With the current forecast track and intensity, winds gusting to low 20s are expected during (Saturday's) window with an increased threat of showers with the close proximity to Emily. Winds continue to strengthen after the window with gusts in the upper 20s to low 30s. The primary concerns for a 24-hour delay are cumulus clouds, disturbed weather and ground winds," forecasters say.

"Emily is forecast to be near South Florida early Saturday morning and near Central Florida late Saturday night through early Sunday morning. The current forecast track is approximately six hours slower than yesterday's forecast. There remains considerable uncertainty in both the forecast track and intensity as Emily interacts with land masses in the Caribbean. After TS Emily exits Western Hispaniola, it is forecast to strengthen to a strong Tropical Storm east of Central Florida," officials say.

In the event of a slip to Sunday, the forecast odds improve to 60 percent favorable for launching Juno.

"In the event of a 48-hour delay, Emily is expected to be off the North Central Florida coast with decreasing winds. Primary concerns for a 48-hour delay are cumulus cloud and disturbed weather."

On the pad! The Atlas 5 rocket has arrived at the Complex 41 pad for tomorrow's ascent with the Jupiter-bound Juno spacecraft.

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 at about seven hours before liftoff time.

The day's 69-minute launch window opens at 11:34 a.m. and closes at 12:43 p.m. EDT.

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The rocket is passing through the pad entrance gate.

The Atlas 5 rocket is emerging from its vehicle assembly building for the journey to the launch pad.

Riding atop a mobile launching platform, the 197-foot-tall space booster is moving to Cape Canaveral's Complex 41 for this much-anticipated flight to send NASA's Juno spacecraft on its trek to Jupiter.

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 was put together inside the assembly building in June and the Juno spacecraft was mounted atop the vehicle last week.

The Atlas 5 is designed to spend minimal time at the launch pad, which does not include a service gantry like other sites.

Tropical Storm Emily is located 838 miles southeast of Kennedy Space Center. The latest forecast says the storm's center will stay offshore the Cape, coming no closer than 120 miles when passing by at 2 a.m. EDT Sunday.

Officials will watch Emily's progress over the next 24 hours before the next critical decision point tomorrow morning. That's when fueling at the Atlas 5 rocket begins during the countdown. Once the cryogenic liquid oxygen and liquid hydrogen begin flowing into the rocket, the time span for rolling the rocket back to the protective assembly hangar grows to nearly a full day.

GO FOR ROLLOUT! With forecasters now predicting Tropical Storm Emily will stay away from Cape Canaveral this weekend, officials have given approval to move the Atlas 5 rocket to the launch pad this morning as planned. Rollout is scheduled to start at 8 a.m. EDT, and we'll have live streaming video coverage on this page!

As of 11 p.m. EDT, Tropical Storm Emily was located south of Hispaniola with sustained winds of 50 mph. The system made a very gradual westward movement this evening and still not started a northerly turn that would keep Emily away from Florida.

"The uncertainty in the track forecast continues to be larger than normal given the current slow motion," the National Hurricane Center said in its 11 p.m. update.

"If a northward component of motion does not begin soon or the track guidance shifts farther to the left in future cycles the threat to Florida and the southeastern United States will increase."

The latest forecast track shows Emily's passage near the Cape late Saturday night. See the map.

While keeping a cautious eye on track and intensity of Tropical Storm Emily, the Atlas 5 rocket is ready for rollout to the launch pad tomorrow in preparation for Friday's blastoff with NASA's Jupiter-bound Juno probe.

Officials gathered earlier today for the Launch Readiness Review and confirmed all technical systems are "go" to continue with pre-flight activities.

Friday's liftoff remains set for 11:34 a.m. EDT (1534 GMT) at the opening of a 69-minute window.

"We had our Launch Readiness Review this morning. Everything went well at that review, all of the systems are ready to proceed with the last two days of our launch campaign and we're really looking forward to getting off the ground on Friday," said Jan Chodas, the Juno project manager.

But the uncertainty with Emily, currently located about 900 miles southeast of Cape Canaveral, has the potential to disrupt the pre-launch activities and keep the Atlas 5 rocket parked inside its assembly hangar.

The 20-story booster is scheduled to be wheeled to the Complex 41 pad tomorrow morning to get the countdown work underway. However, worries about the weather and "what if" scenarios could scuttle the rollout and postpone the launch date.

The National Hurricane Center's broad forecast cone brings the storm through the Bahamas and within close proximity to Florida's eastern coast by Saturday. The weather outlook for Friday's launch time looks good, but officials must weigh the possible risks to the rocket if the countdown attempt is scrubbed.

"Our main concern right now is -- for example -- we make an attempt on Friday and have to scrub that attempt," said Omar Baez, the NASA launch director. "We don't want to leave the vehicle and the spacecraft exposed to the winds and the rain storm. Although structurally it can handle it, it's probably not the wise thing to do."

A team briefing is planned for tomorrow at 6:45 a.m. EDT to review the latest weather outlook and give the final permission to commence the rollout. First motion of the mobile platform from the Vertical Integration Facility is targeted for 8 a.m. EDT.

"So one of the things we're looking for tomorrow is to be able to see how far out we can predict what may or may not happen. Unfortunately right now this storm is not cooperating with us and our timelines," Baez said.

"That decision may have to be delayed or we might have to take a launch delay if it doesn't look favorable for us."

The time it takes for the rocket to retreat back to the safe confines of its vertical hangar varies depending on when that decision is made.

If a Friday scrub occurs prior to fueling, Baez said it still takes "eight hours before we're safely back in the barn."

If the launch team proceeds with a Friday attempt, fuels the rocket with the cryogenic liquid oxygen and liquid hydrogen, and then postpones for some reason, the rollback wouldn't be possible until Saturday. The vehicle must be allowed to warm up before the transfer can occur, approximately a full day after the scrub is called.

Baez summed up the looming decision whether to roll or not: "If you have an optimistic view, it looks okay. If you have the pessimistic view, you might not want to roll out tomorrow because you might be stuck out there and you don't want to do that."

Juno has a 22-day launch period extending from Friday through August 26 to begin its journey from Earth to Jupiter. The timing is dictated by alignment of the planets, and the next shot comes in September 2012.

This rocket's family name has been launching robotic explorers throughout the solar system for nearly 50 years, revolutionizing mankind's knowledge about the planets and our place in the Universe.

From a Cape Canaveral launch pad Friday, the start of NASA's next planetary adventure begins with another Atlas rocket hurling a sophisticated probe away from Earth.

Get to know Juno's ride: The Atlas 5 rocket.

Members of the launch team gathered for the mission dress rehearsal this morning to practice running through the countdown scripts and procedures to be used during Friday's real deal.

Activities remain on track at Complex 41 for blastoff at 11:34 a.m. EDT (1534 GMT).

Meanwhile, weather forecasters have issued their early outlook for the upcoming launch opportunities, predicting a 70 percent chance of acceptable conditions on Friday. Cumulus clouds pose the only concern for violating the launch rules during the day's 69-minute window.

But the picture gets iffy beyond Friday due to developing tropical weather.

"A broad area of low pressure is located near and East of the Lesser Antilles. This wave has high potential to develop over the next several days and should be monitored closely for tropical cyclone development. The system is expected to be in the vicinity of the Southeastern Bahamas on launch day and remaining near the Central to Northern Bahamas and Florida peninsula through the weekend," Air Force meteorologists say.

The specifics at Friday's launch time are expected to include scattered low and high clouds, isolated showers in the area, good visibility, southeasterly winds of 12 to 16 knots and a temperature around 86 degrees F.

If the launch should slip to Saturday for some reason, the odds of acceptable weather fall to 60 percent as the approaching tropical disturbance increases the threat of showers.

In the event of a slip to Sunday, the weather system could be even closer and drop the chance of favorable weather for launching Juno to just 30 percent.

NASA's solar-powered Juno spacecraft will go into orbit around Jupiter's poles to precisely map the planet's gravitational and magnetic fields, probe its turbulent atmosphere and hidden interior and study the mechanisms responsible for its powerhouse auroras, the strongest in the solar system.

Read our mission overview story.

The Flight Readiness Review was held Friday and gave concurrence for pre-mission work to continue for launch next Friday. The FRR is a key milestone that assesses how preparations are proceeding, the issues under analysis and the remaining schedule left until launch day.

A NASA spokesman said after the meeting that "everything has a green light."

The next big tagup is the Launch Readiness Review that occurs on Wednesday to give permission to roll the Atlas 5 rocket to the pad Thursday morning and enter into the countdown.

The Integrated Systems Test for the United Launch Alliance Atlas 5 rocket and the Jupiter-bound Juno orbiter is being run today to confirm the combined booster and payload are ready for their departure from Earth.

"It's the first chance we've had (to test) the entire stack," said John Calvert, the mission manager at NASA's Launch Services Program. "They'll do a tip-to-tail checkout - electrically - of Juno with the launch vehicle to make sure everything is working properly."

Juno and the Atlas have been operating on separate paths during manufacturing and assembly. But they finally met Wednesday, getting bolted together in preparation for that crucial 54-minute ascent next Friday to propel the spacecraft off the ground and out of Earth orbit.

The spacecraft, built by Lockheed Martin, has undergone rigorous testing to ensure the probe's $1 billion mission will proceed without a hitch during the five-year cruise to Jupiter, then gather the unprecedented insights into the giant planet's origins and evolution during 33 polar orbits.

And the rocket had its own test program to pass, which culminated with a practice countdown and fueling exercise at the pad last week that was designed to uncover any problems in advance of the real launch day.

"It gave us a lot of confidence that we'll be ready on launch day," Calvert said. "As always they found a few issues that they're working and will correct in time for the launch."

That Wet Dress Rehearsal on July 19 put the rocket through a life-like countdown simulation, but without the payload loaded aboard. Today's electrical testing couples the rocket and spacecraft together for a final confidence builder.

"We've done a tanking test, so we know the vehicle is good. Now we'll do that final check," Calvert said.

Juno's testing sequence at the Atlas 5 rocket's assembly building got underway today with the space probe's functional checks.

"The on-pad functional test is the first of seven tests and reviews that Juno and its flight team will undergo during the spacecraft's last 10 days on Earth," said Jan Chodas, Juno's project manager from NASA's Jet Propulsion Laboratory in Pasadena, California.

The pre-flight operations will continue tomorrow with the combined Juno and rocket systems test that verifies the electrical connectivity between the spacecraft and the launch vehicle.

"There are a number of remaining prelaunch activities that we still need to focus on, but the team is really excited that the final days of preparation, which we've been anticipating for years, are finally here. We are ready to go," Chodas said.

Workers finished attaching the rocket's nose cone late Wednesday, then retracted the lifting crane a little after 11 p.m. The sliding doors of the Vertical Integration Facility have been closed to provide a comfortable working environment for the team over the next several days.

Rollout of the rocket to the launch pad will occur at 8 a.m. EDT on Thursday, the day prior to liftoff.

With just 9 days left until blastoff, Juno has been placed atop the United Launch Alliance Atlas 5 rocket that will send the spacecraft on its journey to Jupiter.

"I'm incredibly excited. We've been waiting a long time for this and the time is practically here," said Scott Bolton, Juno's principal investigator from the Southwest Research Institute in San Antonio. "It's great to see everything coming together. It's very much a dream come true."

Already packed within the Swiss-made nose cone, the satellite was raised off the ground by overhead cranes and gently maneuvered through the open doorway of the rocket's vertical assembly hangar just after 9 a.m. this morning. It was positioned over the Centaur upper stage and successfully attached at 10:42 a.m. EDT. Work to affix the nose cone's ogive section was continuing late into the evening.

Functional testing of the spacecraft is planned for Thursday, then the combined systems test between Juno and the Atlas vehicle will occur on Friday.

"We'll make sure the satellite is talking to the rocket, the rocket is talking to the satellite and everything is ready," said Mike Woolley of United Launch Alliance.

The fully stacked rocket now stands 20 stories tall. The vehicle features a main stage fed with refined kerosene and liquid oxygen, five strap-on solid propellant boosters, the liquid hydrogen-powered cryogenic Centaur upper stage and a composite payload shroud 16 feet in diameter.

This is the largest, most energetic version of the Atlas 5 rocket currently available. The so-called 551 configuration has been used only once in the previous 26 flights by the vehicle, launching NASA's New Horizons probe to Pluto in 2006.

Hoisting of Juno is underway.

Juno took its middle-of-the-night road trip from Titusville to the Complex 41 launch site, riding aboard a trailer-like transporter from the commercially-run Astrotech satellite processing campus to the Atlas 5 rocket's homebase at the Cape Canaveral Air Force Station.

The slow-moving drive crossed the river, went northward through Kennedy Space Center, passed by the Vehicle Assembly Building and the old space shuttle launch pad before cruising down along the beach to the Atlas rocket's Vertical Integration Facility.

Cranes will hoist the Juno spacecraft into position atop the rocket for attachment to the Centaur upper stage later today.

A robotic space probe destined to orbit Jupiter heads to the rocket assembly building at Cape Canaveral's Complex 41 overnight where the powerful Atlas 5 booster stands waiting for its $1 billion cargo.

NASA's Juno spacecraft has spent the past three-and-a-half months at the Astrotech processing facility near Kennedy Space Center getting ready to depart Earth on its planetary voyage.

Launch remains targeted for August 5 at 11:34 a.m. EDT.

Since arriving in Florida from Lockheed Martin's factory in Colorado on April 8, the craft has been thoroughly tested, its three power-generating solar arrays installed, the maneuvering propellants loaded and spin balancing performed.

Just last week, the two-piece rocket nose cone that shrouds Juno during ascent through the atmosphere was brought into the Astrotech cleanroom and placed around the spacecraft for launch. The encapsulated payload then boarded the motorized transporter for the ride to the Atlas rocket's assembly building at Complex 41.

That road trip is expected to begin between midnight and 1 a.m. EDT.

Juno will be hoisted atop the Atlas on Wednesday.

The rocket convoy began rolling back to the Vertical Integration Facility just after 2 p.m. EDT today to complete the successful Wet Dress Rehearsal. The Juno spacecraft will be brought to the VIF next week for mounting atop its launcher in preparation for blastoff when the planetary window opens August 5.

At Cape Canaveral's Complex 41 today, the Atlas rocket was fueled up for its countdown dress rehearsal.

Clocks ticked down to the final seconds toward a simulated liftoff time just after 2:30 p.m. EDT before the countdown was halted and the rocket safed.

The supercold fuels were offloaded this afternoon and the vehicle allowed to warm up before it is transported back to the assembly building tomorrow.

The United Launch Alliance Atlas 5 rocket that will propel the Juno spacecraft on its voyage to Jupiter was rolled to the Complex 41 pad at Cape Canaveral this morning.

The giant booster consisting of its bronze-colored first stage, Centaur upper stage and five strap-on solid-fuel rockets was recently assembled together atop the mobile launching platform at the Vertical Integration Facility.

This morning's rollout, which took place between 11 a.m. and 12 noon EDT, is part of the Wet Dress Rehearsal activities that each Atlas undergoes prior to launch. The rocket will be fully fueled tomorrow for a realistic practice countdown.

The event is designed to iron out any problems with the hardware and exercise the launch team.

Once the simulated launch day is completed, the rocket will be rolled back to the assembly building for final pre-flight work. Attachment of the Juno payload will occur next week.

Liftoff remains targeted for August 5.

Engineers and scientists eagerly unpacked the Juno spacecraft from its shipping crate Saturday, kicking off nearly four months of launch preparations before the $1 billion mission is shot toward Jupiter this summer.

Read our full story.

Spaceflight Now is providing live coverage of the Juno mission's first steps toward Jupiter. The spacecraft is being transported via an Air Force cargo plane from Denver to Cape Canaveral, and we're on-board to chornicle the journey. See our journal.