An Atlas 5 rocket carrying the most powerful Earth-imaging satellite ever built for the commercial market blasted off from California and streaked into orbit Wednesday, the latest in a series of rapid-fire flights by rocket-builder United Launch Alliance.

Read our full launch story.

T+plus 20 minutes. SPACECRAFT SEPARATION! The WorldView 3 commercial Earth-observing satellite has been released from the United Launch Alliance Atlas 5 rocket, completing today's ascent from Vandenberg Air Force Base in California.

T+plus 16 minutes, 10 seconds. Confirmation has been received that the Centaur main engine cutoff occurred following its burn to inject the WorldView 3 spacecraft into polar orbit.

T+plus 11 minutes. About five minutes remain in this burn of Centaur's single Aerojet Rocketdyne RL10 engine.

T+plus 8 minutes. The RL10 is burning liquid hydrogen and liquid oxygen propellants.

T+plus 5 minutes. The two-halves of the Atlas 5 rocket nose cone encapsulating the spacecraft have separated.

T+plus 4 minutes, 32 seconds. Centaur has ignited! The RL10 engine is up and running at full thrust.

T+plus 4 minutes, 25 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, 15 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, 55 seconds. The RD-180 main engine continues to fire normally, burning a mixture of highly refined kerosene and liquid oxygen.

T+plus 3 minutes, 20 seconds. The engine has throttled down to 92 percent as planned.

T+plus 3 minutes. RD-180 is performing well as the rocket climbs away from the planet.

T+plus 2 minutes, 25 seconds. The rocket now weighs half of what it did at liftoff.

T+plus 2 minutes. Atlas is flying due south from Vandenberg and looking good.

T+plus 85 seconds. Mach 1 as the main engine fires at full throttle.

T+plus 60 seconds. One minute into the ascent. It will take 19 minutes for the two-stage rocket to deploy the satellite into the planned orbit.

T+plus 30 seconds. Pitch, yaw and roll maneuvers have been performed, putting Atlas 5 on the proper heading. The rocket is riding atop 860,000 pounds of thrust from the RD-180 main engine.

T+plus 15 seconds. The launcher is maneuvering to its southerly trajectory to deliver the WorldView observatory into orbit.

LIFTOFF! Liftoff of the Atlas 5 rocket and Worldview 3, the most capable commercial Earth-imaging spacecraft in the world. And the vehicle 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 until the launch. Range is GREEN.

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

T-minus 1 minute, 50 seconds. Liquid oxygen and liquid hydrogen propellant topping to the Centaur upper stage is being secured.

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

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

T-minus 2 minutes, 30 seconds. The first stage RP-1 kerosene fuel tank and the liquid oxygen have stepped up to proper flight pressure levels.

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

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

T-minus 4 minutes and counting. Clocks have resumed for the final minutes of today's countdown to launch the Atlas 5 rocket carrying the WV 3 satellite.

The payload is confirmed on internal power for flight.

Countdown clocks will resume in one minute.

The ULA launch director has given his approval to press onward with the countdown.

All systems are reported "go" to continue with the countdown for liftoff at 11:30:30 a.m. The clocks will resume from this hold at 11:26 a.m.

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 spacecraft payload is switching to internal power.

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

• The 630th launch for Atlas program since 1957
• The 293rd Atlas launch from Vandenberg AFB since 1959
• The 42nd Atlas to use Space Launch Complex 3
• The 9th Atlas 5 launch from Vandenberg AFB since 2008
• The 29th mission for the Centaur upper stage
• The 196th use of Centaur by an Atlas rocket
• The 451st production RL10 engine to be launched
• The 54th flight of the RD-180 main engine
• The 48th launch of an Atlas 5 since 2002
• The 75th Evolved Expendable Launch Vehicle flight
• The 10th commercial launch for Atlas 5
• The 87th United Launch Alliance flight overall
• The 40th Atlas 5 under United Launch Alliance
• The 32nd 400-series flight of the Atlas 5
• The 24th Atlas 5 to fly in the 401 configuration
• The 6th Atlas launch of 2014

Weather is observed GO and forecast GO for launch.

The fuel-fill sequence for the first stage main engine has been completed.

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

-minus 5 minutes and counting. Standing by to go into the final built-in hold that will last for 20 minutes.

The workhorse Centaur upper stage has flown in various configurations for decades. For this launch, the stage will use one Aerojet Rocketdyne-built RL10A-4-2 liquid oxygen/liquid hydrogen engine that develops a thrust of about 22,300 pounds.

The stage is 41.5 feet in length and 10 feet it diameter. It also houses the navigation unit that serves as the rocket's guidance brain.

The Atlas 5 rocket's rigid body first stage is known as the Common Core Booster. The CCB replaced the "balloon" pressure-stabilized stage used by previous Atlas vehicles.

It is equipped with the RD-180 liquid-fueled main engine. This liquid oxygen/kerosene powerplant is a two-thrust chamber, two-nozzle engine.

As the CCB's name suggests, the stage is common and is used in all the various configurations of the Atlas 5 family. The booster stage is 106.6 feet long and 12.5 feet diameter.

This flight builds on the legacy of the Atlas vehicle's 401 configuration, which has flown over 20 times in the past decade with the combination of a four-meter payload fairing, no 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.

But this cargo, the 6,200-pound WorldView spacecraft headed for polar orbit is satisfied with the lifting power of the basic Atlas 5 design.

The vehicle will fly southward away from Vandenberg headed south. Without using an solid motors, however, the rocket won't produce a smokey contrail off the pad.

The Russian RD-180 first stage main engine will ignite at T-minus 2.7 seconds, roaring to full power while undergoing a check to ensure its vital signs are healthy.

Rising off the pad in a slow, majestic fashion, the 19-story Atlas vehicle will deliver nearly a million pounds of ground-shaking thrust for the mid-morning departure.

Four minutes into the flight, staging will occur as the Centaur ignites and the nose cone is jettisoned. The Centaur will burn for about 12 minutes, achieving a circular orbit 380 miles high.

Deployment of the payload to complete the launch sequence is expected 19 minutes.

Now 60 minutes from launch. All activities are proceeding smoothly toward a liftoff at 11:30 a.m. Pacific Time.

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

Fast-filling of the first stage liquid oxygen has been completed at the tank's 97.5 percent mark. Topping mode is now underway.

The Centaur liquid hydrogen tank is 40 percent loaded so far. The cryogenic propellant will be consumed with liquid oxygen by the stage's Aerojet Rocketdyne-made RL10 engine.

Now beyond the three-quarters level of liquid oxygen on the first stage.

Liquid oxygen on Centaur has reached flight level.

Chilldown of the liquid hydrogen system is now complete, allowing the super-cold rocket fuel to begin filling the Centaur upper stage.

First stage liquid oxygen tank is passing the half-full mark. 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 minutes of flight today. The 25,000 gallons of RP-1 were loaded into the rocket earlier.

Now 90 minutes from liftoff. There are no reports of technical troubles from the launch team. Fueling operations remain in work for the launch time of 11:30 a.m. local.

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

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

The Centaur liquid oxygen tank is 75 percent full now.

And the chilldown conditioning of liquid hydrogen propellant lines is starting to prepare the plumbing for transferring the Minus-423 degree F fuel into the rocket. The Centaur holds about 13,000 gallons of the cryogenic propellant.

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

The Centaur liquid oxygen tank is nearing one-quarter full already.

The conditioning of the systems for the first stage liquid oxygen tank have been completed. And a "go" has been given to begin flowing 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 about 50,000 gallons of cryogenic oxidizer for the RD-180 main engine.

Filling of the Centaur upper stage with about 4,300 gallons of liquid oxygen is beginning at Vandenberg's Space Launch Complex 3 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 loaded into the stage a little later in the countdown.

The Centaur liquid oxygen system's 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 has resumed for today's flight of the Atlas 5 rocket following the planned half-hour built-in hold.

Clocks have one more hold scheduled at T-minus 4 minutes. That pause will last 20 minutes during which time the final "go" for launch will be given.

All remains targeted for liftoff at 11:30 a.m. local time (1830 GMT) from Vandenberg Air Force Base, California.

The launch team and all systems are "ready" to proceed with the countdown and begin fueling the Atlas 5 rocket as planned.

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

The Atlas launch conductor is briefing his team on procedures before entering into the final two hours of the countdown. A readiness check of the team members is next.

T-minus 2 hours and holding. The countdown just entered the first of the planned holds over the course of the morning that will lead to the 11:30 a.m. PDT launch of the Atlas-Centaur 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.

Workers have left the pad area in advance of this morning's propellant loading and launch of the Atlas 5 rocket.

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The pad crew reports the gantry is parked, closed up and ready for launch.

The 8-million-pound mobile service tower has been retracted from around the Atlas 5 rocket, revealing the 19-story-tall vehicle for liftoff at 11:30 a.m. PDT today.

The ground crews are getting the gantry's doors closed, plus finishing the final buttoning up of pad equipment over before all workers clear the pad for the remainder of the countdown.

Today's launch will be the ninth Atlas 5 rocket to fly from Vandenberg's Space Launch Complex 3-East pad. The site underwent an extensive overhaul, with construction occurring in 2004 and 2005, to accommodate the larger and more powerful Atlas 5 family of rockets. Some of the major modifications included:

• 30-foot extension to mobile service tower
• 20-foot exhaust duct depth increase
• 250-ton Fixed Launch Platform installed
• Significant ambient and cryogenic fluid ground system modifications
• Complete replacement of the Ground Command/Control/Communication system
• New and refurbished Launch Control/Mission Support Centers

This is the 41st Atlas overall to fly from SLC 3 throughout Vandenberg history.

Rollback of the launch pad's service gantry is underway! This is a major milestone in today's countdown, getting the mobile tower retracted to uncover the Atlas 5 rocket.

The structure's internal crane was instrumental in bringing the rocket stages and payload together. And now the fully assembled Atlas 5 has been unveiled for its 44th launch, the eighth to originate from Vandenberg.

A readiness poll of the team has verified all systems are GO for retraction of the gantry.

Clocks begin ticking now for today's flight by the Atlas 5 rocket from America's western spaceport to deploy the WorldView 3 observatory into space.

As the countdown gets started, the launch team will power up the rocket to conduct standard pre-flight tests and ready the vehicle.

Rollback of the mobile service tower from around the rocket is expected in about three hours. Once the gantry is removed, crews at the pad will make preparations to systems and equipment before the site is cleared of all personnel for fueling.

Supercold liquid oxygen begins flowing into the Centaur upper stage around 9:30 a.m. local, followed by the Atlas first stage. Liquid hydrogen fuel loading for Centaur will be completed a short time later.

A final hold is scheduled when clocks hit the T-minus 4 minute mark. That will give the team 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.

Liftoff remains targeted for 11:30 a.m. local time (2:30 p.m. EDT; 1830 GMT).

The morning's launch window will extend for 15 minutes.

The weather forecast for launch calls for a lingering marine layer by late morning. There is a 40 percent chance of acceptable conditions.

The world's most capable commercial Earth-imaging satellite will be launched into space Wednesday atop an Atlas rocket from Vandenberg Air Force Base in California.

Liftoff is scheduled for 11:30 a.m. local time (2:30 p.m. EDT; 1830 GMT) at the opening of a 15-minute launch window from pad 3-East on South Base.

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