A Delta 4 rocket made a thunderous departure from California on Tuesday afternoon, only to slip into a news blackout minutes later while it climbed higher and faster to deploy a classified spy satellite, a success-defining milestone that was confirmed by hobbyist observers.

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United Launch Alliance has issued a post-launch press release hailing the launch as a success.

"Congratulations to the NRO and to all the mission partners involved in this critical national security launch," said Jim Sponnick, ULA vice president of mission operations. "ULA is proud to have supported this mission and delivered critical capabilities to the men and women defending our freedom throughout the world."

"NROL-25 represents the first of five national security space missions that will be launched by the EELV program over the next four months - including four NRO missions along with the upcoming AEHF 2 launch," the statement said.

The next ULA launch is set for May 5, when an Atlas 5 rocket will launch from Florida with the U.S. Air Force's second Advanced Extremely High Frequency communications satellite.

The official range liftoff time was 4:12:57.278 seconds Pacific time.

The United Launch Alliance Delta 4 rocket has flown into a news blackout. The veil of secrecy surrounding the launch of this clandestine satellite 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, 31 seconds. Now above the discernible atmosphere, the protective nose cone enclosing the secret National Reconnaissance Office satellite payload atop the rocket has jettisoned.

T+plus 2 minutes, 30 seconds. The main engine continues to burn, consuming its liquid hydrogen and liquid oxygen propellants.

T+plus 2 minutes, 15 seconds. The RS-68 is consuming nearly a ton of propellants per second as the powerplant pushes the Delta 4 rocket closer to space.

T+plus 1 minute, 55 seconds. Solid motor separation! The spent boosters have been shed from the first stage. Delta 4 continues powering its way on the thrust generated by the RS-68 main engine.

T+plus 1 minute, 35 seconds. The pair of solid rocket boosters have burned out of their propellant. Standing by for jettison.

T+plus 20 seconds. The Delta 4 rocket is thundering away from Vandenberg on its maiden mission in the Medium+ (5,2) configuration with a pair of solid boosters and five-meter-diameter payload shroud.

LIFTOFF! Liftoff of the Delta 4 rocket on the NROL-25 mission, providing continued space-lifting performance to the U.S. National Reconnaissance Office. And the vehicle has cleared the tower!

T-minus 22 seconds. The hydraulic steering system for the solid rocket motor nozzles has been activated.

T-minus 30 seconds. Green board. All systems remain "go" for launch.

T-minus 40 seconds. Upper stage liquid hydrogen tank is confirmed at flight level.

T-minus 1 minute and counting. The ignition conditions for the RS-68 main engine are "go." The terminal countdown sequencer will take control at T-minus 8.5 seconds. Ignition of the RS-68 powerplant will follow at T-minus 5.5 seconds. The engine powers up to the 102 percent level of thrust for a computer-controlled checkout before liftoff.

T-minus 70 seconds. The Air Force-controlled Western Range has given its "go" for launch.

T-minus 75 seconds. The liquid hydrogen fuel tank on the upper stage is being secured for launch.

T-minus 80 seconds. Upper stage liquid oxygen tank has been secured at flight level.

T-minus 1 minute, 50 seconds. The first stage liquid hydrogen tank has reached flight level and pressure.

T-minus 2 minutes. The rocket's upper stage liquid oxygen tank is being secured.

T-minus 2 minutes, 25 seconds. The liquid oxygen tank in the first stage is confirmed at the proper level and pressure for flight.

T-minus 3 minutes and counting. Ordnance devices aboard the vehicle are being armed.

T-minus 3 minutes, 25 seconds. The systems of the first and second stages of the Delta 4 rocket have switched from ground-fed power to internal batteries for launch.

T-minus 3 minutes, 30 seconds. Replenishment of liquid hydrogen and liquid oxygen to the Common Booster Core first stage is being secured in preparation to pressurize the tanks for launch.

T-minus 4 minutes and counting! Now into the final phase of the countdown for liftoff at 12 minutes past the hour by the Delta 4 rocket carrying a clandestine spacecraft from Space Launch Complex 6 at Vandenberg Air Force Base.

Permission to fly today has been granted by the ULA launch director and Air Force mission director. Standing by to resume the countdown momentarily!

The final readiness polls have been completed and all team members voiced "ready" status for continuing the countdown for launch at 4:12:57 p.m.

Ten minutes to launch! The launch team will be polled in the next few minutes to confirm all systems are "go" to press onward for 4:12 p.m. liftoff.

Assuming all systems remain go, clocks will resume ticking at 4:08:57 p.m. local time. During those final four minutes, the rocket will switch to internal power, ordnance will be armed, all four propellant tanks will be secured and the Range will announce a clear-to-launch.

At T-minus 14 seconds, the sparkler-like radial outward firing ignitors -- or ROFIs -- are started beneath the main engine nozzle. The Terminal Countdown Sequencer will grab control at T-minus 8.5 seconds to manage events in the crucial last seconds and oversee the rocket's status. The ignition sequence for the RS-68 powerplant follows at T-minus 5.5 seconds as the main hydrogen fuel valve is opened. As fuel floods through the engines, spectacular flame erupts at the base of the rocket as free hydrogen reaches the ROFIs.

The oxygen valve in the engine is opened at T-minus 2 seconds as the RS-68 begins roaring to life. The engine must rev up to full throttle -- 102 percent thrust level -- and undergo a rapid computer-controlled health check to ensure all parameters are met.

If any problem is detected before T-minus 40 milliseconds, the engine will shut down and the rocket prevented from lifting off.

A successful engine startup leads to T-0 as the four hold-down bolts that have been restraining the rocket to Earth finally detonate. The 21-story vehicle blasts off at 4:12:57 p.m. (7:12:57 p.m. EDT) on the NROL-25 spy satellite deployment mission.

The launch weather officer reports the winds are now go for launch!

T-minus 4 minutes and holding. The countdown has entered the planned 15-minute hold leading toward the 4:12:57 p.m. liftoff of the Delta 4 rocket.

This pause is designed to give the launch team the opportunity to catch up on any work running behind schedule and verify all is in readiness for the final moments of the count. A series of management polls will be conducted during the hold to give approval to proceed with the launch.

We are now streaming live video of the launch pad as the final countdown progresses toward launch at 4:12:57 p.m. Pacific time (7:12:57 p.m. EDT; 2312:57 GMT).

Hit reload if you're not seeing the video stream.

Ground winds are currently exceeding constraints at the Vandenberg launch pad.

Thirty minutes!

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T-minus 20 minutes and counting. The countdown is headed to the T-minus 4 minute point where a 15-minute hold is planned. Liftoff is targeted for 4:12 p.m., the opening of today's launch opportunity.

Now moving into the final 40 minutes of the countdown.

Today's mission will add a critical new spacecraft to the nation's spy satellite fleet operated by the National Reconnaissance Office.

"They are silent sentinels. They look and listen from the cold reaches of space. They capture signals and images critical to America's intelligence community, warfighters and policymakers. They reveal threats to the homeland, provide battlefield situational awareness, support counter-narcotics, survey the damage from natural disasters and much more. They are the satellites of the National Reconnaissance Office: America's eyes and ears in space," the agency says.

"Today, the U.S. government openly acknowledges the NRO and a variety of users depend on the enormous amount of data NRO satellites collect. Quickly and reliably delivering the information to all 16 intelligence community agencies, the 5 military branches and various civil users and U.S. allies is a critical NRO mission. To do this NRO, from its headquarters in Chantilly, Virginia, builds, operates and maintains a high-speed global information system of satellites and ground-based communications."

The engine slew checks have been performed successfully. The test sequence started with the upper stage RL10 engine, followed by the first stage RS-68 engine gimbaling and then some commanding checks for the strap-on solid rocket motors.

Now 50 minutes away from the NROL-25 launch for the National Reconnaissance Office.

"Today, the United States is preeminent in satellite reconnaissance. The NRO enlists the expertise of highly skilled engineers from across government and industry to maintain this edge in edge in space - the ultimate high ground from which to watch, listen and learn," the NRO says.

"Always vigilant, NRO's eyes and ears give America's policy markers, intelligence analysts, warfighters and homeland security specialists the critical information they need to keep America safe, secure and free."

The countdown is entering the final 60 minutes until the Delta 4 rocket launch from Vandenberg Air Force Base at 4:12:57 p.m. Here's a look at some stats about today's mission. This will be:

• The 359th Delta rocket launch since 1960
• The 19th Delta 4 rocket mission since 2002
• The 4th Delta 4 rocket launch from Vandenberg
• The 15th use of Delta 4 by the Air Force
• The first Medium+ 5,2 configuration to fly
• The second launch of the Delta family in 2012
• The 59th United Launch Alliance mission since 2006
• The 12th Delta 4 under the ULA banner
• The 6th classified Delta 4 for the NRO

The RS-68 first stage main engine spin start pressurization operation is about to start.

That earlier technical issue that the team was discussing is no concern for launch.

With the safety system testing conducted satisfactorily, flight slews of the engines is next in the countdown.

The external inspections of the Delta 4 rocket's thermal insulation following fueling have been completed without any problems seen.

Proper flight conditioning of the upper stage liquid hydrogen and liquid oxygen supplies has been achieved.

The launch team is entering the last 90 minutes of the countdown. With fueling of the Delta 4 rocket completed, team members are monitoring systems while the clocks tick down.

In the immediate future, a series of engine steering tests will occur.

Everything continues to proceed at Vandenberg for liftoff at 4:12 p.m.

Pre-launch checks of the Delta 4 rocket's safety system are being performed at this point in the countdown.

Radio frequency link checks between the rocket and ground have occurred in the most recent portion of countdown operations. ULA reports there are no technical issues standing in the way of launch today.

Now one hour, 45 minutes away from the NROL-25 launch for the National Reconnaissance Office.

"Today, the United States is preeminent in satellite reconnaissance. The NRO enlists the expertise of highly skilled engineers from across government and industry to maintain this edge in edge in space - the ultimate high ground from which to watch, listen and learn," the NRO says.

"Always vigilant, NRO's eyes and ears give America's policy markers, intelligence analysts, warfighters and homeland security specialists the critical information they need to keep America safe, secure and free."

NEW LAUNCH TIME. Liftoff time has been adjusted by a few seconds to the precise moment of 4:12:57 p.m. local.

Proper flight conditioning of the first stage liquid hydrogen supply has been achieved.

Now entering the last two hours of the countdown. Activities are pressing ahead as planned for a liftoff at 4:12 p.m. local time of the Delta 4 rocket from Vandenberg Air Force Base, California.

Upper stage liquid oxygen topping has commenced. That puts all four cryogenic fuel tanks aboard the Delta 4 rocket in topping mode.

Engineers are conducting the standard evaluation of the Delta 4 rocket's thermal insulation following the loading of supercold propellants into the vehicle.

The upper stage liquid hydrogen post-filling checks have been conducted, allowing the tank to be placed into topping mode.

The upper stage liquid oxygen tank has been filled up, now making the Delta 4 a fully fueled rocket for launch at 4:12 p.m. local (7:12 p.m. EDT).

Proper topping and flight conditioning of the first stage liquid oxygen supply has been achieved.

As fueling operations are nearing completion today, the team is off discussing the details of a possible technical problem in the countdown.

Post-fueling venting and valve checks have been completed on the first stage liquid hydrogen tank and its topping phase is being set up for the remainder of the countdown.

A reminder that if you will be away from your computer but would like to receive occasional countdown updates, sign up for our Twitter feed to get text message 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.)

Loading to the upper stage liquid hydrogen tank just ended. The launch team continues to load the liquid oxygen supply to the stage, the last tank left to finish in today's countdown.

Post-filling tests on the first stage liquid oxygen system are complete and the tank has gone into a stable topping mode.

The upper stage conditioning on the liquid oxygen side has finished, so loading of the tank is starting. This is the last of the rocket's four cryogenic supplies to be filled in today's countdown to launch.

The launch team is actively loading the upper stage's liquid hydrogen tank with 10,000 gallons of propellant for the RL10 engine.

The launch team has gotten the approval to start chilldown conditioning of the upper stage liquid oxygen system.

The loading of liquid oxygen into the Common Booster Core first stage has been completed. The launch team will conduct vent and valve checks before putting the tank into topping mode for the rest of the countdown.

Countdown checks of the C-band beacon are beginning. This system is used in tracking the rocket during the flight downrange.

Now four hours till launch. The Delta 4 rocket is being loaded with super-cold liquid oxygen and liquid hydrogen propellants.

Space Launch Complex 6 has two giant sphere-shaped fuel tanks to store the cryogenic liquid oxygen and liquid hydrogen. The LOX tank holds 250,000 gallons and LH2 sphere about 850,000 gallons.

The cryogenics are fed from the storage tanks through pipelines to the pad. For the Common Booster Core first stage, the propellants are routed up to the launch table upon which the rocket sits. Tail service masts, the large box-like structures at the base of the vehicle, feed the oxygen and hydrogen to the booster via separate umbilicals. The upper stage receives its cryos from the top swing arm that extends from the Fixed Umbilical Tower to the front-side of the rocket.

Fast-fill just finished for the first stage liquid hydrogen tank. Topping mode for the supercold propellant will be established shortly.

The chilldown of the upper stage stage liquid hydrogen system is reported complete, clearing the way for loading that tank on the rocket as the countdown rolls on.

First stage liquid oxygen loading continues in progress. "Slow-fill" just finished. The rocket's tank will be loaded with 40,000 gallons of the supercold oxidizer that's chilled to Minus-298 degrees F.

The "go" has been given for the upper stage liquid hydrogen chilldown in advance of fueling.

The first stage liquid oxygen chilldown is complete. Fueling is beginning in the "slow-fill" mode to load a small percentage of the tank. The process then speeds up to the "fast-fill" mode until the tank is nearly full.

Purging preps before fueling are complete on the rocket's upper stage. Those cryogenic loading operations will get started shortly.

First stage liquid hydrogen tanking operation is switching from "slow-fill" to "fast-fill" mode. Some 110,000 gallons of LH2 will load up the rocket's tank.

"Go" for chilldown of the first stage liquid oxygen system. This preps the tank and pumping to guard against shock when the supercold oxidizer begins flowing into the rocket a short time from now.

The cold gas chilldown conditioning of the liquid hydrogen system has been accomplished. Liquid hydrogen propellant will start to flow into the first stage in "slow-fill" mode. That is sped up to "fast-fill" after a small portion of the tank is loaded.

Chilled to Minus-423 degrees Fahrenheit, the liquid hydrogen will be consumed by the RS-68 main engine along with liquid oxygen during the first four minutes of the launch.

The Terminal Countdown is underway for the Delta 4 rocket on the NROL-25 mission to serve the U.S. National Reconnaissance Office. Liftoff remains targeted to occur today at 4:12 p.m. local time from Vandenberg Air Force Base, California.

The multi-step process of loading all four cryogenic propellant tanks in the rocket has begun and will continue into the early afternoon.

If you will be away from your computer but would like to receive occasional countdown updates, sign up for our Twitter feed to get text message 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.)

Now entering the final six hours until liftoff time. We hope to begin our live play-by-play updates on the countdown in a little while.

We have posted a picture gallery taken at Space Launch Complex 6 earlier this morning during rollback of the mobile service gantry.

The 32-story-tall mobile service tower has been retracted from the Delta 4 rocket at Vandenberg's Space Launch Complex 6 pad for today's flight that will place a surveillance satellite into orbit for the U.S. National Reconnaissance Office.

The wheeled structure, a modified piece of hardware from the pad's history as a manned launch site, was moved along rail tracks to its retracted position east of the rocket. The 13-million-pound gantry shielded the Delta from the elements during the stay on the pad since Jan. 5, provided workers 360-degree access to the various areas on the vehicle and was instrumental in attaching the strap-on solid motors and the payload during the launch campaign.

Crews will spend the next couple of hours securing the complex for launch before leaving the danger area around the pad. All workers must be clear of the area for the start of hazardous operations in the countdown, which include fueling the vehicle later this morning.

Liftoff remains scheduled for 4:12 p.m. local. The actual length of the day's available launch window to get the rocket airborne today is not disclosed to the public.

Tower rollback has begun to reveal the United Launch Alliance Delta 4 rocket for flight today!

Retraction of the tower has not started yet. Winds are howling at the pad this morning.

Good morning from Vandenberg Air Force Base where launch day has arrived for the Delta 4 rocket on its hush-hush military mission known simply as NROL-25, a spacecraft-deployment flight for the government agency that operates the nation's spy satellites.

We are standing atop a vista spot just south of Space Launch Complex 6 to photograph retraction of the gantry that will unveil the 21-story-tall rocket, offering the first glimpses of the fully assembled vehicle.


Read our earlier status center coverage.