A powerful Delta 4 rocket roared to life and climbed away from the Cape Canaveral Air Force Station Sunday evening on a high-priority mission to boost a National Reconnaissance Office spy satellite into orbit.

Read our full story.

Some additional post-launch quotes from the 45th Space Wing press release:

"The tremendous ULA, NRO and Air Force partnership once again delivered success," said Lt. Col. William Heuck, 5th Space Launch Squadron commander.

"The Delta 4 rocket continues to evolve and mature with this fourth Delta 4-Heavy launch from the Cape," said Maj. Jeremy Geib, Delta 4 Launch Operations Flight commander. "The team cut Heavy launch processing time over 50 percent."

"This mission helps to ensure that vital NRO resources will continue to bolster our national defense," said Brig. Gen. Ed Wilson, 45th Space Wing commander. "The spectacular evening launch showcases how the 45th assures access to the high frontier and supports global operations."

The initial portion of tonight's launch of the United Launch Alliance Delta 4-Heavy rocket carrying a payload for the National Reconnaissance Office has been called a success.

"This second Delta 4-Heavy launch for the NRO is the culmination of years of hard work and dedication by the combined NRO, Air Force, supplier, and ULA team," said Jim Sponnick, ULA vice president, Mission Operations.

"ULA is pleased to support the NRO as it protects our nation's security and supports our warriors defending our nation around the world.

"This launch also tops off another exceptional year for ULA. We are proud to have launched 45 missions in 48 months since our inception Dec. 1st, 2006."

A quick picture of the blastoff.

The Delta 4-Heavy rocket has flown into a news blackout. The veil of secrecy surrounding the launch of this classified satellite means no further information about the progress of the upper stage engine firings and release of the payload will be announced in real-time.

All previous Heavy launches saw the upper stage perform three firings in missions that targeted circular orbits at geosynchronous altitude 22,300 miles above the planet. It's fully anticipated that tonight's mission will be another three-burn profile that follows an ascent timeline similar to the one demonstrated during the 2004 test flight and used again in the 2009 launch for the NRO. That would mean the upper stage performs its first two burns in quick succession, reaching a typical geosynchronous transfer orbit by T+plus 30 minutes, then takes an exceptionally long coast before delivering a final boost to circularize the orbit and releasing the payload to complete the launch about six hours after liftoff.

In any event, the ultimate outcome of the launch will remain a mystery, as far as the public is concerned.

T+plus 6 minutes, 40 seconds. The 65-foot-long, tri-sector nose cone that enclosed the classified National Reconnaissance Office satellite during ascent through the atmosphere has jettisoned.

T+plus 5 minutes, 58 second. Engine start! The Pratt & Whitney Rocketdyne RL10B-2 cryogenic rocket engine is up and burning for the first of three firings during tonight's launch of the Delta 4-Heavy.

T+plus 5 minutes, 48 seconds. Pyrotechnics have detonated to jettison the spent center Common Booster Core. The rocket's upper stage and attached payload are now flying free.

T+plus 5 minutes, 40 seconds. Main engine cutoff! The center booster's RS-68 engine has finished firing and shut down.

T+plus 4 minutes, 45 seconds. The center Common Booster Core's RS-68 engine has revved up to full throttle for the Delta 4-Heavy rocket's on-going journey to space. The booster is identical to the outer strap-on stages, carrying the same propellant supply and engine package, but it employed a more conservative fuel consumption strategy over the past three minutes. That has left enough cryogenic fuel to fire nearly 90 seconds longer.

T+plus 4 minutes, 12 seconds. The 15-story tall starboard and port Common Booster Cores that provided the vast majority of thrust during the first four minutes of flight have expended their fuel and peeled away from the center stage. Tiny solid-fueled motors on the discarded boosters gave helpful nudges to ensure a clean separation. The boosters will tumble into the Atlantic Ocean below.

T+plus 4 minutes, 10 seconds. Engine cutoff! Standing by for booster separation.

T+plus 3 minutes, 35 seconds. Coming up in about 20 seconds, the outer Common Booster Cores will throttle down as a precursor to engine shutdown and jettison of the stages. It will take five seconds to ease the power setting to 57 percent. The boosters will operate at that throttle for another five seconds before the RS-68s are shut down.

T+plus 3 minutes, 10 seconds. The Delta 4-Heavy rocket is 28.6 miles in altitude and 45 miles downrange from the launch pad.

T+plus 3 minutes. The Delta 4-Heavy now weighs half of what it did at liftoff. The rocket is burning vast amounts of cryogenic propellant to accelerate away from the planet.

The center engine remains at 57 percent thrust while the starboard Common Booster Core's engines are firing at 102 percent. The outer boosters have just over one minute remaining in powered flight.

T+plus 2 minutes, 20 seconds. The Delta 4-Heavy rocket is 15 miles in altitude and 11 miles downrange from the launch pad.

T+plus 2 minutes. The 8-foot diameter bell-shaped nozzles on the three main engines gimbal during flight, allowing the rocket to steer itself on the intended trajectory eastward across the Atlantic Ocean and toward space.

T+plus 1 minute, 45 seconds. The outer Common Booster Cores and their RS-68 main engines continue to consume the supply of super-cold liquid hydrogen and liquid oxygen rocket fuel while firing at full throttle. The RS-68 is considered the world's largest hydrogen-fueled rocket engine. Each powerplant is capable of generating 17 million horsepower.

T+plus 1 minute, 30 seconds. The vehicle is ascending through the flight regime that provides the maximum aerodynamic pressures on the rocket. This period is called Max-Q. And the Delta 4-Heavy is breaking the sound barrier as its speed reaches Mach 1.

T+plus 60 seconds. One minute into the flight of the Delta 4-Heavy.

T+plus 55 seconds. The center Common Booster Core's main engine is throttling back to 57 percent thrust as a fuel conservation effort. The starboard and port boosters continue to operate at their maximum power setting of 102 percent thrust.

T+plus 30 seconds. All three Pratt & Whitney Rocketdyne RS-68 main engines are firing at full throttle, gulping three tons of propellant per second to produce 1.9 million pounds of thrust.

T+plus 15 seconds. The vehicle has cleared the towers at Complex 37 to begin pitch and roll programs that will place the rocket on the proper heading to fly eastward from Cape Canaveral.

T-minus 10, 9, 8, 7, 6, ignition sequence start, 3, 2, 1, engines running, commit, and LIFTOFF! Liftoff of the Delta 4-Heavy rocket, guarding America's security with another critical satellite launch for the National Reconnaissance Office!

T-minus 15 seconds. America's heavy-lift rocket, the towering white and orange triple-barreled booster responsible for launching vital security and intelligence satellites, is ready to make another of its spectacular ascents from Cape Canaveral.

T-minus 30 seconds. The terminal countdown sequencer will take control at T-minus 8.5 seconds. Ignition of the three RS-68 powerplants will follow at T-minus 5.5 seconds. The engines power up to the 102 percent level of thrust for a computer-controlled checkout before liftoff.

T-minus 40 seconds. Upper stage liquid hydrogen tank now secure at flight level.

T-minus 60 seconds. The three RS-68 main engines are ready for ignition.

T-minus 70 seconds and counting. The Eastern Range has given its "go" for launch.

T-minus 80 seconds. The upper stage liquid oxygen tank has been verified at flight level.

T-minus 90 seconds and counting. All systems are "go" with a minute-and-a-half remaining in the countdown.

T-minus 1 minute, 45 seconds. The three Common Booster Core liquid hydrogen tanks have reached flight levels and pressures.

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

T-minus 2 minute, 30 seconds. The liquid oxygen tanks in the three Common Booster Cores are confirmed at the proper levels and pressures for flight.

T-minus 3 minutes and counting. Replenishment of liquid hydrogen and liquid oxygen to the three Common Booster Cores is being secured in preparation to pressurize the tanks for launch.

T-minus 4 minutes and counting. Ordnance devices aboard the vehicle are being armed.

T-minus 4 minutes, 30 seconds. The systems of the Common Booster Cores and upper stage of the Delta 4-Heavy rocket are switching from ground-fed power to internal batteries for launch.

T-minus 5 minutes and counting! Clocks are running again for launch of the Delta 4-Heavy rocket on the NROL-32 classified satellite-deployment mission for the National Reconnaissance Office. Liftoff is set to occur at 5:58 p.m. EST (2258 GMT) from pad 37B at Cape Canaveral Air Force Station, Florida.

Now six minutes from launch! The ULA launch director has given final approval to resume the countdown as planned.

The government mission director has granted permission to launch at 5:58 p.m. EST.

The launch pad swing arm retraction system pins are being pulled. The three arms will be rotated away from the Delta 4 rocket at liftoff.

The final pre-flight poll of the launch team confirms all systems are "ready" for liftoff of the Delta 4-Heavy rocket and its spy spacecraft payload this evening. The targeted launch time is 5:58 p.m. EST.

Now 10 minutes away from the NROL-32 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."

One minor technical issue has been analyzed and determined to be no constraint to flight.

T-minus 5 minutes and holding. The countdown has just entered a planned hold point. Clocks will remain here for 15 minutes to give the launch team members a chance to finish any work running behind schedule and mission officials to conduct final readiness checks. Liftoff is still targeted for 5:58 p.m. EST.

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."

Weather is go! The clouds that had been a problem have passed by.

T-minus 15 minutes. The countdown clocks will be going into a planned hold at the T-minus 5 minute mark. Liftoff remains targeted for 5:58 p.m. EST.

The weather officer says the back edge of the specific cell that's violating the cumulus cloud rule should pass in about 20 minutes. Once that happens, weather will be "go" for launch.

The launch team reports no problems are being worked and liftoff remains on schedule.

Radio frequency link checks are being performed to verify good telemetry streams between the rocket and the receiving station at the Cape.

Steering checks of the Delta 4 rocket's engines have been conducted. The upper stage RL10 engine and the three Common Booster Core main engines were put through slew tests to confirm the rocket will be able to steer itself properly during ascent.

The countdown is entering the final 60 minutes until the Delta 4-Heavy rocket launch from Cape Canaveral at 5:58 p.m. EDT. Here's a look at some stats about today's mission. This will be:

• The 351st Delta rocket launch since 1960
• The 14th Delta 4 rocket mission since 2002
• The 12th Delta 4 rocket launch from Cape Canaveral
• The 4th Heavy configuration to fly
• The 7th Delta 4 under the ULA banner
• The 3rd Delta 4 launch this year
• The 10th use of Delta 4 by the Air Force
• The 3rd classified Delta 4 for the NRO

Weather is "no go" at this time due to violation of the cumulus cloud rule. Forecasters expect the specific clouds that are the problem will clear about an hour from now. There's no violation of the flight thru precipitation rule right now and the shower may skirt the pad after all.

Launch time is 90 minutes away. The rocket has been filled up with fuel for the mission. But as the countdown continues, all eight propellant tanks will be replenished to replace the cryogenics that naturally boil away. Topping mode is underway for all eight tanks.

Today's mission will be the fourth for the heavy-lift varient of the Delta 4 family. The towering white and orange triple-barreled booster is responsible for launching vital security and intelligence satellites.

The initial launch was a demonstration test flight conducted in December 2004. The first operational mission in November 2007 orbited a missile-warning satellite for the U.S. military. The National Reconnaissance Office's first use of the vehicle came in January 2009 with a geosynchronous eavesdropper.

The NRO's plans for the Heavy following this launch include a flight early next year from Vandenberg Air Force Base in California and another from Cape Canaveral in late 2011.

The upper stage liquid oxygen tank has been loaded and the Delta 4-Heavy rocket now stands fully fueled for launch.

The weather officer says the flight thru precipitation and cumulus cloud rules could go "red" about 15 minutes from now. It could take upwards of 90 minutes to clear out, right near the target liftoff time. There is nothing behind this approaching band, so forecasters remain optimistic for getting the rocket off the ground today.

Filling of the upper stage liquid oxygen tank is finishing as fueling nears completion.

Just two hours left to go until liftoff time. Weather conditions remain within the allowable limits right now. But there's some more showers just off the coastline moving this way.

The post-loading checks for the Common Booster Cores liquid hydrogen tanks have been completed ahead of topping. The team is proceeding into the upper stage hydrogen checks now.

Last night marked the eighth anniversary of the Delta 4 rocket's maiden mission, a successful debut that launched a commercial communications satellite into orbit for Paris-based Eutelsat. The program has flown a dozen addition times since then, carrying out flawless deployments of Air Force communications, navigation, weather and missile-warning spacecraft, National Reconnaissance Office spy satellites and civilian geostationary weather observatories.

See our full archive of Delta rocket flights.

The latest update from the launch weather team still puts odds at 80 percent chance of acceptable conditions for liftoff today.

The official launch forecast calls for scattered-to-broken stratocumulus clouds at 4,000 feet, showers in the vicinity, 7 miles of visibility, a temperature between 68-70 degrees F and easterly winds from 080 degrees at 10 peaking to 15 knots.

Fast-fill loading of the upper stage liquid hydrogen tank just wrapped up.

The chilldown of the upper stage liquid oxygen system is reported complete, clearing the way for loading the rocket's tank with 4,500 gallons. This is the last of the rocket's eight cryogenic supplies to be filled in today's countdown to launch.

Post-loading checks of the Common Booster Core liquid oxygen systems have been accomplished and the tanks are going into topping mode.

The launch team is starting the chilldown thermal conditioning of the upper stage liquid oxygen system. This is the last tank left to fill today.

As the countdown proceeds toward launch this evening, you can follow along right here on this page.

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Three hours and counting as the United Launch Alliance team works to get the Delta 4-Heavy rocket fully fueled with cryogenic propellants for today's launch. Liftoff remains scheduled for 5:58 p.m. EST.

The weather is back in a "go" status again. The specific cumulus clouds that were violating launch criteria and the rain shower over the pad have moved out of the way now. It's still cloudy, obviously, but the current conditions at Complex 37 are within limits for a liftoff. And the forecast remains optimistic of weather allowing a launch today.

Fast-fill loading of the upper stage liquid hydrogen supply is starting. The tank will be loaded with 10,000 gallons of propellant for the RL10 engine.

The loading of liquid oxygen into the Common Booster Cores has been completed. The launch team will be performing vent and relief checks following tanking and begin chilldown procedures for the upper stage liquid oxygen system.

Fast-fill loading of the liquid hydrogen tanks on the three Common Booster Cores has been completed. Some 110,000 gallons of LH2 are put into the rocket's tanks for flight. Vent and relief checks will be performed shortly.

The liquid oxygen loading is progressing as planned for the three Common Booster Cores. Each tank will be loaded with about 40,000 gallons of supercold LOX.

With the CBC liquid hydrogen tanking continuing, the launch team has been given approval to begin chilldown conditioning of the upper stage liquid hydrogen system. This is a precursor to fueling the upper stage.

Now four hours till launch. The Delta 4 rocket's three Common Booster Cores currently are being loaded with super-cold liquid oxygen and liquid hydrogen propellants.

Complex 37 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 three Common Booster Cores, 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 boosters via separate umbilicals. The upper stage receives its cryos from the middle swing arm that extends from the Fixed Umbilical Tower to the front-side of the rocket.

No problems or issues are being worked in the countdown and the launch team says activities are proceeding on schedule for a liftoff at 5:58 p.m. EST. Weather remains cloudy and drizzly, but forecasters say there's good odds of conditions permitting a launch this evening. At the current moment, the launch rules for cumulus clouds and flight thru precipitation are red.

With the Common Booster Cores' liquid oxygen systems properly conditioned for cryogenic temperatures, the loading of Minus-298 degree LOX into the Delta 4-Heavy rocket is beginning. The liquid oxygen tanks in all three Common Booster Cores will be filled over the next hour or so. The oxidizer will be consumed by the RS-68 main engines during launch.

The liquid hydrogen loading is switching to the "fast-fill" mode.

And now the liquid oxygen chilldown is starting in advance of feeding the cryogenic oxidizer into the Delta 4-Heavy rocket.

The cold gas chilldown for the hydrogen side has been completed and the launch team is beginning the initial loading of liquid hydrogen propellant into the three Common Booster Core stages. This "slow-fill" will be sped up to "fast-fill" after a small portion of each tank is loaded.

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

The launch team is getting into the fueling operations procedures now. The cold gas chilldown conditioning of the Common Booster Cores for liquid hydrogen fueling has begun.

Fueling activities will start with thermal conditioning steps to ready equipment for pumping the super-cold liquid oxygen and liquid hydrogen propellants into the Delta 4-Heavy rocket.

T-minus 5 hours, 15 minutes and counting! The second Terminal Countdown is underway for the Delta 4-Heavy rocket on the NROL-32 mission to serve the U.S. National Reconnaissance Office. With one final hold planned at T-minus 5 minutes, liftoff is still targeted to occur at 5:58 p.m. EST.

The multi-step process of loading all eight cryogenic propellant tanks in the rocket is scheduled to begin in the next half hour and continue into the late afternoon.

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T-minus 5 hours, 15 minutes and holding. A pre-planned one-hour hold has started ahead of the Terminal Countdown sequence. During this time the full launch team will be seated at the consoles, the pad is scheduled to be cleared of all workers and readiness polls will be conducted by mission management to ensure everyone is ready to proceed with the count.

The Terminal Count begins when the clocks resume ticking at 12:28 p.m. EST, leading toward a liftoff of the Delta 4-Heavy rocket at 5:58 p.m. EST from Cape Canaveral.

The weather forecast for today's launch opportunity now predicts an 80 percent chance of acceptable conditions for liftoff. Those odds are down slightly because of the cloud cover and rain showers streaming ashore from the Atlantic.

It has been a gloomy and wet morning around the Space Coast today.

"Localized coastal effects have increased the coverage of scattered showers along the near shore waters over the past couple of days. These showers will move onshore throughout the day, mainly over areas the south of the Cape. As a result, the overall probability of weather constraint violation has increased, although confidence remains high that favorable conditions will exist at times throughout the launch window," the Air Force weather team reported this morning.

The official launch forecast calls for scattered-to-broken stratocumulus clouds at 4,000 feet, showers in the vicinity, 7 miles of visibility, a temperature between 68-70 degrees F and easterly winds from 080 degrees at 10 peaking to 15 knots.

The two weather rules at risk of being violated and holding up the launch will be cumulus clouds and flight through precipitation.

The mobile service gantry is moving away from the rocket right now, clearing the way for the second launch countdown to commence. The multi-hour fueling operations will begin in the early afternoon as clocks target a blastoff time just after the sun goes down.

Here's the official statement from ULA about the rescheduling the launch for Sunday:

"The launch of the United Launch Alliance Delta 4-Heavy with a National Reconnaissance Office payload is rescheduled for Nov. 21, at 5:58 p.m. EST.

"Following the scrubbed Nov. 19 launch attempt, the launch team examined the port and starboard common core strap-on boosters in the areas where they received anomalous temperature data signatures during Friday's launch countdown. After inspections by engineers, it was determined that the temperature data signatures were caused by issues with two temperature sensors. New temperature sensors have been installed and tested, which has resolved the issue.

"The Delta 4-Heavy rocket and NRO payload are safe and secure.

"The current weather forecast calls for a 90 percent chance of acceptable weather for Nov. 21."

Officials announced a few moments ago that launch will be targeted for Sunday at 5:58 p.m. EST (2258 GMT). The weather outlook is 90 percent favorable.

Be sure to check out must-see images of the Delta 4-Heavy rocket from Pat Corkery, ULA's photographer, taken earlier today. The photo gallery is posted here.

United Launch Alliance says details on rescheduling the Delta 4-Heavy rocket flight won't be settled tonight and liftoff isn't going to happen on Saturday. We'll pass along the new launch date when it is announced.

With the Delta 4-Heavy launch postponed, attention now turns to Alaska where the U.S. Air Force and Orbital Sciences are preparing to fly a Minotaur 4 rocket carrying a cache of small satellites into orbit. Spaceflight Now is live at the Kodiak Launch Complex with updates and streaming video of the mission.

Here's the official statement from ULA about the delay:

"The launch attempt of the United Launch Alliance Delta 4-Heavy with a National Reconnaissance Office payload was scrubbed today. During the launch countdown, anomalous temperature data signatures were detected on the port and starboard strap-on common core boosters during cryogenic fueling. When detected, mission managers halted the countdown and stopped further tanking of the rocket. After evaluation, the decision was made to scrub today's launch attempt. Mission managers are currently studying the situation to determine a corrective action plan.

"The Delta 4-Heavy and payload are safe and secure at this time. When a decision is made confirming the date of the next launch attempt it will be announced."

SCRUB. Today's launch attempt for the Delta 4-Heavy rocket has been called off due to a problem that arose during fueling operations. The vehicle is safe and secure. But time will be needed to assess the issue and officials just determined that liftoff won't be possible this evening. There's no immediate word about a new launch date.

NEW LAUNCH TIME. Liftoff is being retargeted for tonight at 8:30 p.m. EST (0130 GMT).

The launch team remains on standby right now, hoping the issue can be resolved and fueling resumed for liftoff tonight. Here's an update from rocket-maker United Launch Alliance:

"During today's cryogenic fueling, anomalous temperature readings were observed on the port and starboard strap-on common core boosters. At this time, fuel loading has ceased and the launch countdown is on hold. Mission managers are currently studying the situation to see if this can be satisfactorily resolved to continue with today's launch attempt."

The troubleshooting and go-forward plans continue to be worked. Launch still can happen tonight, albeit a little later than 6:06 p.m. EST. The rocket's available liftoff window extends a few hours, which could enable the problem to be fixed, fuels reloaded and the launch to occur this evening.

The offloading of liquid hydrogen is being stopped. Officials are still assessing whether the team can overcome the earlier problem and still launch tonight.

Still in a holding pattern after some sort of problem arose during fueling operations. The rocket is being drained of what cryogenics had been loaded aboard.

Countdown clocks are continuing to tick despite the stop in fueling. Awaiting official word on the plan going forward.

The team is proceeding into liquid hydrogen offloading.

Flow of liquid oxygen to the rocket has stopped and technicians are starting to offload the commodity.

We have posted a gallery of pictures taken at pad 37B this morning after rollback of the mobile service gantry. The images can be seen here.

With the Common Booster Cores' liquid oxygen systems properly conditioned for cryogenic temperatures, the loading of Minus-298 degree LOX into the Delta 4-Heavy rocket is beginning. The liquid oxygen tanks in all three Common Booster Cores will be filled over the next hour or so. The oxidizer will be consumed by the RS-68 main engines during launch.

The liquid hydrogen loading is switching to the "fast-fill" mode.

And now the liquid oxygen chilldown is starting in advance of feeding the cryogenic oxidizer into the Delta 4-Heavy rocket.

The cold gas chilldown for the hydrogen side has been completed and the launch team is beginning the initial loading of liquid hydrogen propellant into the three Common Booster Core stages. This "slow-fill" will be sped up to "fast-fill" after a small portion of each tank is loaded.

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

No issues are being worked in the countdown and the launch team says activities are proceeding on schedule.

The cold gas chilldown conditioning of the Common Booster Cores for liquid hydrogen fueling has begun.

The "go" has been given for fueling operations. The launch team will start thermal conditioning steps to ready equipment for pumping the super-cold liquid oxygen and liquid hydrogen propellants into the Delta 4-Heavy rocket today.

T-minus 5 hours, 15 minutes and counting! The Terminal Countdown has commenced for today's launch of the Delta 4-Heavy rocket and a satellite payload for the U.S. National Reconnaissance Office. With one final hold planned at T-minus 5 minutes, liftoff is still targeted to occur at 6:06 p.m. EST.

The multi-step process of loading all eight cryogenic propellant tanks in the rocket is scheduled to begin in the next half hour and continue into the late afternoon.

Weather continues to look beautiful for the Delta 4-Heavy rocket's launch. There's just a few scattered clouds, light winds and temperatures in the low 70s F right now.

The call to "man stations for Terminal Count" is sounding to the launch team.

T-minus 5 hours, 15 minutes and holding. Clocks have been paused for a planned one-hour hold, during which time the full launch team will be seated at their consoles, the launch pad is scheduled to be cleared of all workers and readiness polls will be conducted by mission management to ensure everyone is ready to proceed with the count.

The Terminal Countdown begins when the clocks resume ticking at 12:36 p.m. EST, leading toward a liftoff of the Delta 4-Heavy rocket at 6:06 p.m. EST from Cape Canaveral.

It is launch day at Cape Canaveral Air Force Station for the Delta 4-Heavy rocket carrying a reconnaissance satellite for the U.S. intelligence community. Liftoff of America's largest unmanned space booster is scheduled for 6:06 p.m. EST.

The mobile service tower has been moved away from the rocket, allowing workers to proceed onward with today's checklist of chores needed to configure and secure the pad for the countdown.

Rollback began a little before 7:30 a.m. and the tower was clear of the Heavy about 10 minutes later. The gantry reached its parking spot around 7:45 a.m.

The Terminal Count is scheduled to begin at 12:36 p.m. EST, some five-and-a-half hours before the targeted liftoff time. The countdown will be spent fueling the eight cryogenic fuel tanks aboard the rocket, testing critical systems and verifying the hardware is ready to fly.

At 5:46 p.m., the countdown enters a planned 15-minute hold at the T-minus 5 minute mark. This offers managers a chance to perform final readiness polls of the entire launch team to confirm there are no issues or concerns before entering the last phase of the countdown.

Assuming all systems are go, clocks will resume ticking at 6:01 p.m. During those final five minutes, the rocket will switch to internal power, ordnance will be armed, all eight 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 nozzles. 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 three RS-68 powerplants follows at T-minus 5.5 seconds as the main hydrogen fuel valve in each engine 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 valves in the engines are opened at T-minus 2 seconds as the RS-68s begin roaring to life. The engines 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 engines will shut down and the rocket prevented from lifting off.

A successful engine startup leads to T-0 as the 12 hold-down bolts that have been restraining the rocket to Earth finally detonate. The 23-story, 1.6-million pound vehicle blasts off at 6:06 p.m. EST (2306 GMT) on the NROL-32 spy satellite deployment mission.

Each booster core features a Pratt & Whitney Rocketdyne RS-68 main engine that generates 650,000 pounds of thrust while burning supercold liquid hydrogen and liquid oxygen.

About 50 seconds into flight, the center Common Booster Core's engine is throttled back to its minimum power level of 57 percent thrust to conserve fuel that becomes important later. The starboard and port boosters continue firing at full throttle -- 102 percent thrust -- through the launch's first four minutes before emptying their liquid hydrogen and liquid oxygen propellant tanks and shutting down the RS-68 engines. The 15-story boosters will peel away and plummet into the Atlantic Ocean.

Once the outer boosters are shed, the center stage finally throttles back up to 102 percent for more than a minute of propulsion, consuming that fuel supply saved during the period of reduced thrust. Once the stage is jettisoned, the rocket's cryogenic upper stage powered by a Pratt & Whitney Rocketdyne RL10B-2 engine will continue the push to orbit.

The 65-foot-long shiny white metallic nose cone, originally developed to shroud payloads on Titan 4 rockets, is jettisoned after the upper stage is ignited.

Soon thereafter, the launch will enter a news blackout and no further information about the secretive mission is expected.

Ground crews are busy in the predawn hours getting launch pad 37B prepared for today's 6:06 p.m. EST sendoff of the Delta 4-Heavy rocket carrying a critical spy satellite.

Retraction of the 330-foot tall mobile service tower from around the rocket is expected to begin a little later this morning. The wheeled gantry structure moves along rail tracks to its launch position about the length of a football field from the rocket's mount.

The 9-million pound tower shields the Delta 4 from the weather, provides workers 360-degree access to the various areas on the vehicle and is needed to hoist the payload atop the upper stage during the launch campaign. The tower is 90 feet wide and 40 feet deep.

The Cape's Complex 37 is the same site used in the 1960s to fly unmanned Saturn 1 and 1B rockets that helped prepare for mankind's voyage to the moon. The site was rebuilt for the Delta 4 era, successfully supporting 11 liftoffs in the next-generation vehicle family so far.

Air Force meteorologists are predicting good weather conditions for a Friday liftoff of the Delta 4-Heavy rocket from Cape Canaveral. There is a 90 percent chance of acceptable conditions, with ground-level winds posing only a slight concern.

Today's weather: "Stalled cold frontal boundary over southern Florida. Widespread low level cloudiness and chance for an isolated shower will decrease during the day as drier air moves in from the north," the weather team says.

The outlook: "Surface high pressure center located north of the area will move eastward providing a northeast onshore wind on launch day, and remainder of week. On Friday, local conditions will consist of northeast winds, post frontal stratocumulus clouds, and temperatures near normal for mid-November. The only item of interest will be the strength of the onshore winds as they will approach but remain below the 20-knot liftoff constraint."

The forecast for Friday night's launch window includes some scattered clouds at 3,000 feet, 7 miles of visibility, a temperature between 66-68 degrees F and northeasterly winds from 030 degrees at 12 peaking to 18 knots.

The odds of acceptable weather on Saturday and Sunday, if the launch should be delayed, are 90 percent favorable both nights.

Launch of the Delta 4-Heavy rocket has been delayed by 24 hours to fix an issue with ground pyrotechnics that release the big booster at liftoff. The new launch opportunity is scheduled for Friday evening at 6:06 p.m. EST (2306 GMT).

Here is rocket-maker United Launch Alliance's press statement:

"During closeout processing of the launch system in preparation for flight, engineers detected that the installation of some ground support equipment pyrotechnic ordnance lines did not meet requirements. These ordnance lines fire the 'hold down bolts' at liftoff releasing the Delta 4-Heavy for flight. Mission managers have delayed the launch 24 hours, which allows time for new ordnance lines to be installed that meet all flight requirements.

"The Delta 4-Heavy rocket and NRO payload are safe and secure. The current weather forecast calls for a 90 percent chance of acceptable weather for Nov. 19."

One cannot overstate the importance of Thursday night's Delta 4-Heavy launch from Cape Canaveral to national security, a mission by the massive rocket that will deploy "the largest satellite in the world" to hear the whispers of evil.

Read our preview story.

As pre-flight preparations continue as planned for Thursday's countdown, meteorologists at the 45th Weather Squadron have bumped up the odds of favorable launch conditions to 90 percent.

The forecast continues to call for just a few clouds, good visibility, a temperature around 67 degrees F and north-northwesterly winds of 12 peaking to 18 knots. The limit is 20 knots, and that's what the weather team will be watching.

If the launch should slip to Friday night, the outlook will be much of the same. The forecast for Saturday brings the change of rain into the equation.

The early weather projections for Thursday night's launch of the Delta 4-Heavy rocket carrying a clandestine spy satellite calls for good conditions at Cape Canaveral Air Force Station.

Meteorologists issued their initial forecast this morning and put the odds of acceptable launch weather at 80 percent. Gusty winds at pad 37B will pose only a slight concern.

"Conditions aloft will feature a relatively flat, progressive pattern with low pressure trough moving across the northern tier of the U.S. and off the eastern seaboard. At the surface, a low pressure center will develop along the northwestern Gulf Coast states on Monday and quickly move northeastward. An accompanying weak cold front will move through central Florida during the day on Wednesday. Surface high pressure will build in across Florida behind the front and be the main feature on launch day, and remainder of week," forecasters say.

"On Thursday local conditions will consist of north-northwest winds, post frontal stratocumulus clouds mainly over the ocean, and temperatures near normal for mid-November. The only item of interest will be the strength of the post frontal ground level winds as they will approach but remain below the 20-knot liftoff constraint."

The forecast calls for a few low clouds at 3,000 feet and a few high clouds at 25,000 feet, 7 miles of visibility, a temperature between 68-70 degrees F and north-northwesterly winds from 340 degrees at 12 peaking to 18 knots.

The evening's launch window opens at 6:10 p.m. EST (2310 GMT) for this mission to deploy a payload for the National Reconnaissance Office. The NRO is the government agency responsible for the country's fleet of intelligence-gathering satellites.

Watch this page for continuing pre-flight status and live coverage throughout Thursday's countdown.

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