A United Launch Alliance Atlas 5 rocket put on a display of power, sound and light Friday evening at Vandenberg Air Force Base in launching a clandestine national security payload, then successfully debuted a new upper stage engine as it flew over the horizon.

Read our launch story.

MISSION SUCCESS. The Atlas 5 rocket has successfully delivered its clandestine payload into orbit today, debuting the new RL10C-1 engine in the process.

"We are honored to deliver the NROL-35 spacecraft to orbit together with our customers, the NRO Office of Space Launch and the Air Force," said Jim Sponnick, ULA vice president, Atlas and Delta Programs.

"This mission was launched on the most powerful Atlas ever launched from California with more than 2 million pounds of liftoff thrust. This was enabled by the addition of the four solid rocket motors, providing additional performance as required to meet our customer’s needs."

This was the inaugural flight of the Aerojet Rocketdyne RL10C-1 engine.

"ULA is extremely pleased with this first flight of the new, RL10C-1 engine," said Sponnick. "We have been working closely with Aerojet Rocketdyne and our Air Force customers for several years to develop and extensively test this next-generation engine to enable the most reliable and cost-effective upper stage propulsion for our Atlas and Delta programs."

"This launch was an incredible achievement for Team Vandenberg, ULA, NRO and our other fellow launch partners," said Col. Keith Balts, 30th Space Wing commander and the launch decision authority.

"This Atlas 5 launch marked the last of the year and I am very proud of the teamwork that led to the success of not only today's launch, but those that preceded. The hard work and dedication of everyone involved continues to ensure our nation's access to space. This was especially evident by our base electricians who worked tirelessly through last night's extreme weather to ensure power was available for launch."

The United Launch Alliance Atlas 5 rocket has flown into a pre-arranged news blackout following jettison of the rocket's payload shroud. The veil of secrecy surrounding the launch of this clandestine satellite cargo means no further information about the progress of the ascent, upper stage engine firings or release of the payload will be announced in real-time.

T+plus 3 minutes, 20 seconds. The two-halves of the Atlas 5 rocket nose cone encapsulating the 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. 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, 55 seconds. All four of the Aerojet Rocketdyne-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 the mission.

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 thunders away from the Central Coast with its RD-180 engine and four solid rocket boosters burning.

LIFTOFF! Liftoff of the most powerful Atlas to ever launch from Vandenberg Air Force Base. And the vehicle has cleared the tower!

T-minus 20 seconds. "Go Atlas", "Go Centaur" "GO L-35" 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 NROL-35 satellite payload.

The ULA launch director and the NRO mission director have given their approval to press onward with the countdown.

All systems are reported "go" to continue with the countdown for liftoff at 7:19 p.m. The clocks will resume from this hold at 7:15 p.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.

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

• The 633rd launch for Atlas program since 1957
• The 294th Atlas launch from Vandenberg AFB since 1959
• The 43rd Atlas to use Space Launch Complex 3
• The 10th Atlas 5 launch from Vandenberg AFB since 2008
• The 222nd mission for the Centaur upper stage
• The 199th use of Centaur by an Atlas rocket
• The 455th production RL10 engine to be launched
• The 57th flight of the RD-180 main engine
• The 51st launch of an Atlas 5 since 2002
• The 79th Evolved Expendable Launch Vehicle flight
• The 11th National Reconnaissance Office use of Atlas 5
• The 91st United Launch Alliance flight overall
• The 43rd Atlas 5 under United Launch Alliance
• The 17th 500-series flight of the Atlas 5
• The 3rd Atlas 5 to fly in the 541 configuration
• The 9th Atlas launch of 2014

NEW LAUNCH IIME is being set for 7:19 p.m.

Weather is observed GO and forecast GO for launch.

Liquid oxygen and liquid hydrogen tanks are at flight level.

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 and 30 seconds.

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

The workhorse Centaur upper stage has flown in various configurations for decades. For this launch, the stage will use one Aerojet Rocketdyne-built RL10C-1 liquid oxygen/liquid hydrogen engine that develops a thrust of about 22,890 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.

Now 60 minutes from launch. All activities are proceeding smoothly toward a liftoff at 7:14 p.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. Topping mode is now underway.

The Centaur liquid hydrogen tank is 50 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.

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 7:14 p.m. local.

NEW LAUNCH TIME. The target liftoff time has been adjusted slightly to 7:14:00 p.m. local (0314 GMT).

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.

The Centaur liquid oxygen tank is nearing 40 percent 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 7:13 p.m. local time (0313 GMT) from Vandenberg Air Force Base in 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 day that will lead to the 7:13 p.m.local 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 today's propellant loading and launch of the Atlas 5 rocket.

Guidance system testing is complete.

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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 20-story-tall vehicle for liftoff at 7:13 p.m. PST 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 10th 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

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 51st launch, the 10th to originate from Vandenberg.

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

Atlas and Centaur have been powered up. Guidance system testing is next.

The countdown begins anew for tonight's launch of the Atlas 5 rocket from Vandenberg Air Force Base in California. Liftoff is scheduled for 7:13:30 p.m. local time (10:13:30 p.m. EST; 0313:30 GMT).

"Any of the folks who get to watch this launch, which will be an evening launch, will really get to see a show both in sound and light produced," said Lt. Col. Jim Bodnar, 4th Space Launch Squadron commander at Vandenberg.

Last night's initial countdown was halted due to a bleak weather forecast. Conditions are predicted to improve for tonight's try, with a 40 percent chance of acceptable conditions.

"We've got a weather squadron here on base that provides us frequent updates on the weather, including probabilities of violations of the many weather constraints," Bodnar said.

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, 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.

"Looking forward to NROL-35. So many people...so much preparation...so much riding on the Atlas 5...so much fun to be a part of," tweeted Col. Keith Balts, 30th Space Wing commander and the launch decision authority.

The weather forecast shows a 40 percent chance of acceptable conditions for tomorrow's launch attempt.

SCRUB. A rainy weather forecast for drought-stricken California has forced officials to delay Thursday night's planned launching of an Atlas 5 rocket with a classified reconnaissance satellite payload.

Liftoff has been reset for Friday evening at approximately 7:13 p.m. local time (10:13 p.m. EST; 0313 GMT) from Vandenberg Air Force Base.

Officials made the rare decision to delay the mission ahead of time. But the forecast predicted rain, thick clouds gusty winds and even lightning would violate weather rules tonight.

This first time in 17 Atlas launches, dating back to 2012, that a scrub has occurred after the countdown was initiated. The consecutive string had been fueled and launched on the first attempts.

Officials are receiving an updated weather forecast and will caucus on the results.

Atlas and Centaur have been powered up. Guidance system testing is next.

Clocks begin ticking now for today's flight by the Atlas 5 rocket from America's western spaceport to deploy the NROL-35 payload 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, 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 7:17 p.m. local time (10:17 p.m. EST; 0317 GMT).

An Atlas 5 rocket has been cleared to launch Thursday evening from Vandenberg Air Force Base in California to deploy a classified national security payload, weather permitting.

Officials held the Launch Readiness Review today and gave approval to enter into the countdown on Thursday morning.

Liftoff is targeted for 7:17 p.m. local time at the opening of a secret launch window.

But the weather could put spoil the liftoff plans. Meteorologists give only 10 percent odds that the weather will allow the launch to occur.

"We're really excited about this mission," said Capt. Jason Krahmer, the launch's mission manager with the 4th Space Launch Squadron. "It is the first Atlas 5-541 configuration that we've launched out of Vandenberg. So it's quite an exciting time for us here."

The 20-story rocket will be the most powerful Atlas ever flown from Vandenberg.

"The Atlas 5-541 configuration puts out about two million pounds of thrust at liftoff, so it's quite comparable to the Delta 4-Heavy which is 2.1 million pounds," Krahmer said.

"A lot of folks got to see the recent Minuteman 3 launch about a month ago. Each one of the solid rocket boosters on the Atlas is about the same size and produces approximately the same thrust as a Minuteman 3 ICBM," said Lt. Col. Jim Bodnar, 4th Space Launch Squadron commander at Vandenberg.

What's more, the launch also debuts the new RL10C-1 upper stage engine.

"This is the first use of the RL10C upper stage engine. This was actually an engine that was converted from an RL10B (used by Delta 4). This marks a significant milestone in the development of a common upper stage engine across both the Atlas 5 and Delta 4 launch vehicles," Krahmer said.

Rainy weather at the California launch site is forecast to put a damper on plans to fly an Atlas 5 rocket on Thursday evening.

Read our full story.

The most powerful Atlas rocket to ever fly from the West Coast is poised for launch Thursday to deliver a secret payload into orbit while debuting a new upper stage engine.

Read our full story.