RECAP STORY: A clandestine satellite for the U.S. reconnaissance program was successfully launched by an Atlas 5 rocket today, riding a ferocious torrent of fire and smoke off the pad before disappearing behind a curtain of secrecy.

Read our launch story.

This was the 135th successful Atlas program launch in a row spanning more than two decades and the 64th for an Atlas 5.

The next Atlas 5 rocket launch from Cape Canaveral, a 411-configured vehicle with one solid-fuel booster, is planned for Sept. 8 to send NASA's OSIRIS-REx sample return spacecraft on a 7-year trek to Asteroid Bennu and back. Liftoff will occur during a two-hour launch window opening at 7:05 p.m. EDT (2305 GMT).

"Superb launch success for the EELV Atlas 5/NROL-61 team!" tweeted Lt. Gen. Samuel Greaves, the Space and Missile Systems Center commander and Air Force program executive officer for space. "Congrats! Laser Focus on Mission Success!"

MISSION SUCCESS is declared in this morning's satellite launch performed by the Atlas 5 rocket from Cape Canaveral.

"Thank you to the entire mission team for years of hard work and collaboration on today’s successful launch of NROL-61. We are proud the U.S. Air Force and NRO Office of Space Launch have entrusted ULA with delivering this critical asset for our nation’s security,” said Laura Maginnis, ULA vice president of Custom Services.

"Our continued one launch at a time focus and exceptional teamwork make launches like today’s successful."

A video replay of today's launch is posted here.

To recap, the United Launch Alliance Atlas 5 rocket departed Cape Canaveral atop 1.5 million pounds of thrust at 8:37 a.m. EDT (1237 GMT) today to deliver the classified NROL-61 payload into space for the U.S. National Reconnaissance Office.

It is the 64th Atlas 5 launch and the rocket's 13th for the NRO.

We will pause our live updates at this time. Check back later for confirmation of a completed mission.

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 4 minutes, 43 seconds. The two halves of the 14-foot-diameter Atlas 5 rocket nose cone encapsulating the spacecraft have separated.

T+plus 4 minutes, 32 seconds. Centaur has ignited! The RL10C engine is up and running at full thrust to put the NROL-61 payload into orbit.

T+plus 4 minutes, 22 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, 30 seconds. The vehicle weighs just a quarter of what it did at liftoff.

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, 40 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 2 minutes, 35 seconds. Atlas continues tracking on course.

T+plus 2 minutes, 20 seconds. The RD-180 main engine continues to perform as expected.

T+plus 2 minutes, 10 seconds. Both 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 2 minutes. The vehicle weighs just half of what it did 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. The period of maximum dynamic pressure experienced by the rocket has been passed as we are one minute into the ascent of the NROL-61 satellite.

T+plus 50 seconds. Mach 1.

T+plus 30 seconds. The vehicle is heading on a flight azimuth of 99 degrees.

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 twin solid rocket boosters burning.

LIFTOFF! Liftoff of the Atlas 5 rocket, enabling security through the National Reconnaissance Office!

T-minus 20 seconds. "Go Atlas", "Go Centaur" and "Go NROL-61" 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 55 seconds. Range is green.

T-minus 1 minute. Now 60 seconds away from launching the National Reconnaissance Office's latest mission.

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 are enabled.

T-minus 4 minutes and counting. Clocks have resumed for the final minutes of today's countdown to launch the Atlas 5 rocket from Cape Canaveral, Florida.

Standing by to pick up the count.

The ULA launch director and the National Reconnaissance Office mission director have given their respective final approvals to resume the countdown.

Polling of the team by Atlas launch conductor just occurred. All systems are reported GO for flight.

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 Atlas 5 rocket stands 194 feet tall and weighs 950,000 pounds at launch.

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

• The 646th launch for Atlas program since 1957
• The 351st Atlas launch from Cape Canaveral
• The 235th mission of a Centaur upper stage
• The 212th use of Centaur by an Atlas rocket
• The 470th production RL10 engine to be launched
• The 13th RL10C-1 engine launched
• The 70th flight of the RD-180 main engine
• The 64th launch of an Atlas 5 since 2002
• The 53rd launch of an Atlas 5 from Cape Canaveral
• The 4th Atlas 5 launch of 2016
• The 96th Evolved Expendable Launch Vehicle flight
• The 23rd EELV flight for National Reconnaissance Office
• The 13th National Reconnaissance Office use of Atlas 5
• The 109th United Launch Alliance flight overall
• The 56th Atlas 5 under United Launch Alliance
• The 23rd NRO launch by United Launch Alliance
• The 78th United Launch Alliance flight from Cape Canaveral
• The 43rd 400-series flight of the Atlas 5
• The 6th Atlas 5 to fly in the 421 configuration
• The 45th NRO launch since acknowledging flights in 1996
• The 22nd NRO launch from the Cape
• The 3rd NRO launch this year

The vehicle's three cryogenic tanks are at flight level.

T-minus 4 minutes and holding. The countdown has entered the planned 15-minute hold to give the launch team a chance to review all systems before pressing ahead with liftoff.

T-minus 6 minutes. Standing by to go into the final built-in hold.

Weather is observed GO for liftoff based on the current conditions and forecast to stay favorable for an 8:37 a.m. EDT (1237 GMT) launch today.

Just 30 minutes until liftoff time. 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 fuel-fill sequence for the first stage main engine is starting.

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.

Augmenting thrust for today's launch are two solid-propellant boosters made by Aerojet Rocketdyne. Considered the world's longest monolithic -- or single-segment -- solid boosters, the motors provide the extra thrust needed to increase the Atlas 5's payload-carrying capacity.

Each booster stands 67 feet tall, has a diameter of just over five feet and weighs 102,000 pounds at launch. The slender white rockets have a lightweight graphite epoxy casing with an erosion-resistant insulation. The solid fuel is high-performance class 1.3 HTPB propellant.

Now 45 minutes from liftoff. Today marks the 64th flight for Atlas 5, born of the Air Force's competition to develop next-generation Evolved Expendable Launch Vehicles. In its previous 63 missions since debuting in August 2002, the Atlas 5 has flown 25 flights dedicated to the Defense Department, 14 commercial missions, 12 for NASA and 12 with spy satellites for the National Reconnaissance Office.

The million-pound Atlas 5 rocket now stands fully fueled with its cryogenic liquid oxygen and liquid hydrogen as the countdown continues on schedule for a liftoff at 8:37 a.m. EDT (1237 GMT).

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

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

Now 60 minutes from liftoff.

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

Centaur's liquid hydrogen tank is 30 percent full. The cryogenic propellant will be consumed with liquid oxygen by the stage's Aerojet Rocketdyne-made RL10C 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 minutes of flight today. The 25,000 gallons of RP-1 were loaded into the rocket after rollout on Tuesday.

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 first stage liquid oxygen tank has reached the 50 percent mark.

The Centaur engine chilldown sequence is being initiated.

Centaur liquid oxygen tank has reached flight level.

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

The first stage liquid oxygen 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 12,300 gallons of the cryogenic propellant.

Now half-full on the Centaur upper stage's liquid oxygen tank.

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 48,800 gallons of cryogenic oxidizer for the RD-180 main engine.

Passing the 10 percent level on the Centaur upper stage's liquid oxygen tank.

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 RL10C engine along with liquid hydrogen to be pumped into the stage a little later in the countdown. The Centaur will perform the firings required to propel the NROL-61 satellite into its intended 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 2 hours and counting! The launch countdown has resumed for today's flight of the Atlas 5 rocket on a mission to deploy the U.S. National Reconnaissance Office's NROL-61 satellite into space.

Clocks have one more built-in hold planned at T-minus 4 minutes. During that 15-minute pause, the final "go" for launch will be given. All remains targeted for liftoff at 8:37 a.m. EDT (1237 GMT) from Cape Canaveral's Complex 41.

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

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

The loading of nearly 66,000 gallons 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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The danger area has been cleared of all personel.

T-minus 2 hours and holding. The countdown has just entered the first of two planned, 15-minute holds over the course of the day that will lead to the 8:37 a.m. EDT (1237 GMT) launch of the Atlas rocket. The holds give the team some margin in the countdown timeline to deal with technical issues or any work that is running behind. The final hold is scheduled to occur at T-minus 4 minutes.

The final hands-on work has wrapped up at the launch pad and technicians are departing the complex. Safety officials will confirm that the surrounding danger area has been cleared of all workers for the remainder of the countdown.

The early portion of the countdown has been going well. There are no issues being reported in the count, activities are on schedule and the weather is fine.

In today's first weather briefing to mission managers, all current conditions are observed GO for launch of the Atlas 5 rocket and odds for the launch window stand at 90 percent favorable.

Conditions are stable this morning across Cape Canaveral and the launch weather officer says there is little concern for violating any of the launch criteria.

The outlook predicts just a few low- and high-level clouds, good visibility, southerly winds of 7 to 11 knots and a temperature of 81 degrees F.

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

The countdown just began for today's launch of the Atlas 5 rocket on a national security satellite deployment flight for the U.S. government.

Clocks are picking up the seven-hour sequence of work that will prepare the booster, payload and ground systems for blastoff at 8:37 a.m. EDT (1237 GMT).

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

A planned 15-minute hold begins when the count reaches T-minus 2 hours. Near the end of the hold, the team will be polled to verify all is in readiness to start fueling the rocket for launch.

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

A final hold is scheduled at the T-minus 4 minute mark. That 15-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.

The launch window length this morning is classified.

The seven-hour countdown begins overnight for the United Launch Alliance Atlas 5 rocket to haul a top-secret payload into space for the nation's spy satellite agency.

Tomorrow's liftoff is targeted for 8:37 a.m. EDT (1237 GMT).

Although the countdown and liftoff will occur in public view, the ascent will go into a news blackout about five minutes into flight due to the secret nature of the payload for the National Reconnaissance Office.

No details are available about the satellite's identity, its mission or operational orbit.

"With its vigilance from above, the NRO gives America's policymakers, intelligence analysts, warfighters and homeland security specialists the critical information they need to keep America safe, secure, and free," the NRO website says.

The rocket was positioned atop Complex 41's launch pad on Tuesday morning, following rollout from the nearby vehicle assembly building. Today is a crew rest "sync day" for the overnight countdown coming up.

See photos of Tuesday's rocket rollout.

Weather forecasters predict a 90 percent chance of acceptable conditions for the launch opportunity.

"High pressure and favorable weather conditions will continue over the next 72 hours," forecasters say.

"Tomorrow morning, deep mid-level dry air remains over Central Florida resulting in very favorable weather conditions. Winds will be weak from the south with gusts in the 7 to 11 kt range during the window. The primary concern for launch is Cumulus Clouds."

The launch time outlook calls for a few low- and high-level clouds, good visibility, southerly winds of 7 to 11 knots and a temperature of 81 degrees F.

Watch this page for live coverage throughout the countdown and morning flight of the Atlas-Centaur rocket.

Be sure to sign up for our Twitter feed to get occasional countdown updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

Playalinda Beach is an ideal public viewing spot for the launch. The location puts you less than five miles from the launch pad to feel the 1.5 million pounds of liftoff thrust! Get directions here.

PREVIEW: An Atlas 5 rocket carrying a classified national security satellite was rolled to the launch pad this morning for Thursday's flight to bolster the U.S. intelligence-gathering space architecture.

Read our full story.

WEATHER: Good weather for launching a rocket is forecast for Cape Canaveral and the Space Coast on Thursday morning when a United Launch Alliance Atlas 5 is scheduled to take flight.

Read our full story.