The clandestine cargo carried into polar orbit Thursday aboard the first California-launched Delta 4-Heavy rocket was a crucial replacement satellite for the nation's surveillance and security network, amateur sky-watchers say.

Read our full story.

We have posted launch photo galleries from Surf Beach and sound-activated cameras at Space Launch Complex 6.

Some additional post-launch quotes from the 30th Space Wing press release:

"The teamwork between the 30th Space Wing, the National Reconnaissance Office, United Launch Alliance and numerous other agencies was outstanding for our first-ever Delta 4-HLV from Vandenberg Air Force Base," said Col. Keith Balts, 30th Space Wing vice commander and Launch Decision Authority. "I'm very proud to be part of the team who worked so hard to make this mission a success."

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

"Today's launch was the second Delta 4-Heavy launch for the NRO in two months and was also the largest rocket ever launched from the West Coast," said Jim Sponnick, ULA vice president, Mission Operations.

"Most important is the critical NRO payload launched today which will significantly enhance the effectiveness and safety of the brave men and women defending our nation every day. Today's successful launch represents the culmination of five years of hard work and exceptional skill in modifying the launch system to establish the West Coast heavy lift capability for the nation and to integrate this important mission.

"I congratulate the combined NRO, Air Force, supplier and ULA team on this impressive accomplishment and successful launch."

The Delta 4-Heavy 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 upper stage engine firings and release of the payload will be announced in real-time.

It is believed by satellite watchers and military analysts that the rocket has launched a telescope-like surveillance spacecraft that continues the long-line of Keyhole birds. "It is generally accepted that NROL-49 is an electro-optical imaging intelligence satellite of the KH-11 lineage, which were built by Lockheed Martin," said Ted Molczan, a respected sky-watcher who keeps tabs on orbiting spacecraft.

Molczan believes the satellite going up today will replace the aging craft originally deployed in 2001.

Experts say the imaging satellites have powerful vision with ultra-high resolution to monitor the globe for U.S. national security.

T+plus 6 minutes, 20 seconds. The nose cone that enclosed the classified National Reconnaissance Office satellite during ascent through the atmosphere has jettisoned.

T+plus 5 minutes, 58 seconds. Engine start! The Pratt & Whitney Rocketdyne RL10B-2 cryogenic rocket engine is up and burning for the first firing during today'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, 15 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 Pacific 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. 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. 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 southward over the Pacific 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 on its maiden mission from the West Coast in service to the nation.

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 of the launch pad and risen into view from here at the beach. The Delta 4-Heavy is majestically firing into the blue skies with three distinct red-hot main engine plumes trailing 20 stories long for the flight southward.

T-minus 10, 9, 8, 7, 6, ignition sequence start, 3, 2, 1, engines running, commit, and LIFTOFF! Liftoff of the Delta 4 rocket from Space Launch Complex 6, establishing America's new heavy-lift path to polar orbit!

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 Western 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 for the Delta 4-Heavy rocket's first launch from California.

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-49 classified satellite-deployment mission for the National Reconnaissance Office. Liftoff is set to occur at 1:10:30 p.m. local (4:10:30 p.m. EST; 2110:30 GMT) from Space Launch Complex 6 at Vandenberg Air Force Base, California.

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 1:10:30 p.m. Pacific.

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 afternoon. The targeted launch time is 1:10:30 p.m. local (4:10:30 p.m. EST; 2110:30 GMT).

Now 10 minutes away from the NROL-49 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."

Assuming all systems remain go, clocks will resume ticking at 1:05:30 p.m. Pacific Time. 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 1:10:30 p.m. PST (4:10:30 p.m. EST) on the NROL-49 spy satellite deployment mission.

T-minus 5 minutes and holding. The countdown has just entered a planned hold point. Clocks will remain here for 17 minutes, 30 seconds to give the launch team members a chance to finish any work running behind schedule and mission officials to conduct final readiness checks.

T-minus 10 minutes. The countdown clocks will be going into a planned hold at the T-minus 5 minute mark. Liftoff remains targeted for 1:10 p.m. local time.

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."

Steering checks of the Delta 4 rocket's engines are complete and satisfactory. 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 Vandenberg Air Force Base at 1:10 p.m. local time. Here's a look at some stats about today's mission. This will be:

• The 352nd Delta rocket launch since 1960
• The 15th Delta 4 rocket mission since 2002
• The 3rd Delta 4 rocket launch from Vandenberg
• The 5th Heavy configuration to fly
• The 8th Delta 4 under the ULA banner
• The 11th use of Delta 4 by the Air Force
• The 4th classified Delta 4 for the NRO

The team is now preparing to conduct steering checks of the Delta 4 rocket's engines.

Launch time is 75 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.

The rocket's safety systems are being checked by personnel to verify that equipment is ready for launch.

A sizable crowd is building at Vandenberg's Surf Beach, located about 7 miles north of the pad. This is the closest vantage point for watching the launch.

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

Today's mission will be the fifth 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. A repeat mission for the NRO with another such communications-interceptor went up last November.

The NRO's plans for the Heavy following this launch include another from Cape Canaveral this December. There's also an additional Vandenberg mission slated for late 2013 or early 2014.

NEW LAUNCH TIME! The target launch time is being adjusted by two-and-a-half minutes to 1:10:30 p.m. Pacific (4:10:30 p.m. EST; 2110:30 GMT). This change was prompted by the COLA, or collision avoidance safety measures. COLA cutouts ensure the rocket isn't launched on a course that would take it too close to another object already in space.

To recap, fueling operations have progressed smoothly today at Space Launch Complex 6. The rocket's Common Booster Cores are in topping mode for liquid hydrogen and liquid oxygen. The upper stage liquid hydrogen is being topped off, too. The liquid oxygen supply will start topping shortly, after some post-loading checks are completed.

Loading of the upper stage liquid oxygen tank just finished, meaning the Delta 4-Heavy rocket now stands fully fueled for launch.

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 1:08 p.m. Pacific Time.

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.

The upper stage liquid oxygen system will take 4,500 gallons. This is the last of the rocket's eight cryogenic supplies to be filled in today's countdown to launch.

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

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

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.

Weather is chilly but gorgeous right now at Vandenberg Air Force Base, hoping for the clear skies to continue through launch time.

The loading of liquid oxygen into the Common Booster Cores just finished. 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 upper stage liquid hydrogen supply is starting. The tank will be loaded with 10,000 gallons of propellant for the RL10 engine.

Loading of the liquid hydrogen tanks on the three Common Booster Cores in fast-fill mode 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.

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 five 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.

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 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 top swing arm that extends from the Fixed Umbilical Tower to the front-side of the rocket.

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

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 as planned.

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 fueling operations procedures are beginning now. 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 6 hours, 15 minutes and counting! The Terminal Countdown has commenced for the Delta 4-Heavy rocket on the NROL-49 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 1:08 p.m. Pacific Time.

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

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No issues are being reported in the countdown and activities are tracking right on the planned timeline this morning.

The launch team has been polled to ensure all stations are manned and systems are ready to proceed with the Terminal Countdown.

We have posted a couple of pictures taken at Space Launch Complex 6 earlier this morning after rollback of the mobile service gantry. The images can be seen here.

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

T-minus 6 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.

The Terminal Count begins when the clocks resume ticking at 6:38 a.m. local (9:38 a.m. EST), leading toward a liftoff of the Delta 4-Heavy rocket at 1:08 p.m. (4:08 p.m. EST) from Vandenberg Air Force Base, California.

All systems remain "go" for Thursday's launch of the Delta 4-Heavy rocket, America's largest unmanned space booster, carrying a reconnaissance satellite for U.S. national security.

The weather outlook continues to forecast a 90 percent chance of acceptable conditions for the 1:08 p.m. local (4:08 p.m. EST; 2108 GMT) launch time.

Exceptionally large crowds are expected at Vandenberg Air Force Base and the surrounding areas to witness the 23-story vehicle roar into the sky on nearly two million pounds of ground-shaking thrust.

"Everybody's pretty excited to see the Big One, as it's called. Over the past year, we've literally hosted thousands of distinguished visitors to the launch pad -- senior Department of Defense, industry, foreign dignitaries. It's been great to show off what we do to them, but a lot of them want to come back now," said Lt. Col. Brady Hauboldt, the Air Force launch director and Vandenberg's 4th Space Launch Squadron commander.

The triple-wide rocket will trail fiery plumes from the three main engines as it majestically climbs into the afternoon sky and heads downrange on a southward trajectory over the Pacific.

At about 8:30 a.m. this morning, crews at Space Launch Complex 6 retracted the 27-story mobile assembly shelter away from the rocket. This 9-million-pound structure, which moves along rails, was built in the 1980s when the pad was being prepared for space shuttle launches. It was designed to shield the shuttle from the weather during on-pad assembly of the vehicle's solid rocket boosters, external tank and mating of the orbiter.

In the predawn hours on Thursday, the 32-story, 13-million-pound mobile service tower that actually wraps around the Delta 4-Heavy to provide workers access to the rocket will be rolled back to fully unveil the space launcher.

Although this is the Heavy's maiden mission from California, the rocket has performed four flights from Florida's Cape Canaveral for the Air Force and National Reconnaissance Office.

"This vehicle is very similar to previous Heavy launches from the Cape. The most recent launch of the Delta 4-Heavy in November was carefully dissected by Space and Missile Systems Center and Aerospace Corp. for any flight or mechanical crossovers which apply to this launch. We've learned a lot about the Heavy vehicle from those previous launches," Hauboldt said.

The rocket has been standing atop the pad since last January 29, participating in extensive testing with the upgraded ground support equipment and ensuring this first West Coast Heavy will give its vital payload a successful ride to orbit.

"Launch is the riskiest part of any space mission...so we spend a lot of time making sure everything is perfect," Hauboldt said.

The final launch readiness reviews have been completed and the countdown is about to begin for the big booster's blastoff.

Ever since the final Titan 4 rocket soared over the horizon from Vandenberg Air Force Base five years ago, the nation lacked the ability to deploy the largest of reconnaissance satellites into polar orbits from the West Coast. But that gap will be closed when the modernized replacement -- the Delta 4-Heavy -- makes its California debut on Thursday.

See our full story.

Forecasters are predicting ideal weather for Thursday's launch of the Delta 4-Heavy rocket from Vandenberg Air Force Base, California.

As high pressure dominates the West Coast with fair weather and warmer temperatures, meteorologists are putting the odds of acceptable launch conditions at 90 percent. Winds at Space Launch Complex 6 will pose only a slight concern.

The forecast calls for a few high cirrus clouds at 25,000 feet, 7 miles of visibility, a temperature between 62-67 degrees F and northwesterly winds of 10 peaking to 15 knots.

For the backup launch opportunity on Friday, similar conditions are expected and chances of acceptable weather remain at 90 percent.

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

And 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.)

Check out this special feature story about this history of Space Launch Complex 6 from manned spaceflight projects to the Delta 4-Heavy rocket.

The excitement is building at California's Vandenberg Air Force Base for next Thursday's launch of the biggest rocket ever from the West Coast -- the Delta 4-Heavy.

Liftoff of the giant rocket, standing 23 stories tall, remains scheduled for 1:08 p.m. (4:08 p.m. EST; 2108 GMT) to deploy a critical national security satellite into space.

"This is the point where it gets real, real exciting. I've been working on this since the day I took this job a year and a half ago. It has consumed a large portion of what the entire squadron has done and the base has done," Lt. Col. Brady Hauboldt, the 4th Space Launch Squadron commander, said in an interview Thursday.

The Space Launch Complex 6 underwent an extensive upgrade to outfit the pad and ground systems with the capability to support the triple-barreled booster.

United Launch Alliance's Delta 4-Heavy is America's largest unmanned rocket currently in service, capable of lofting the heftiest cargos. The mammoth vehicle is created by taking three Common Booster Cores -- the liquid hydrogen-fueled motor that forms a Delta 4-Medium's first stage -- and strapping them together, then adding a powerful upper stage.

"It's great to finally get to this point. We're through most of our senior reviews, we're heading into the final launch preparations and closeouts, which means we're almost there. The launch and space vehicle are ready to go at this point, the base infrastructure is ready to go. Now we're just focused on the final closeouts and keeping our eye on the weather for next week," Hauboldt said.

The launch recently delayed a couple of times, enabling technicians to resolve concerns and ensure the rocket will operate perfectly during its climb to orbit.

"Recent issues that we have had prompting our delay have been addressed. We've done some removal and replacement of a few suspect parts and we're back now to our normal in-line processing," Hauboldt said.

A final round of readiness reviews are planned for next Tuesday and Wednesday, leading into Thursday's launch countdown activities that begin before dawn, Hauboldt added.

(For more insight about 4th Space Launch Squadron, see our earlier feature story from last September)

Officials have delayed the Delta 4-Heavy rocket launch by three days. Liftoff is reset for Thursday, January 20.

The target launch time for next Monday's Delta 4-Heavy rocket has been announced to the public. Liftoff from Vandenberg Air Force Base is scheduled for 1:08 p.m. local (4:08 p.m. EST; 2108 GMT).

The exact duration of the daily launch window hasn't been disclosed.

As we count down to the upcoming Delta 4-Heavy rocket on its maiden West Coast flight from the same launch pad once built for military space shuttle missions, let's look back a quarter-century to the time when Enterprise stood atop Space Launch Complex 6 for testing. It was 1985 and the prototype shuttle was checking out the pad at Vandenberg Air Force Base, California.

Eventually, the whole idea of launching the shuttle from there was cancelled, but the pad lives on and will support the unmanned Delta 4-Heavy liftoff on Jan. 17.

So check out these comprehensive photo collections that document Enterprise's time at Vandenberg beginning with a tour of the shuttle inside its hangar on North Vandenberg.

The shuttle then took a road trip over Vandenberg's hilly terrain and reached Space Launch Complex 6 for attachment to the external fuel tank and solid rocket motors at the pad.

Once the vehicle was put together, the pad structures were retracted to unveil the fully assembled shuttle. There's even a page of nighttime views with Enterprise.

The launch control center was located right at the pad, too. Take a look inside.

And one last page with more beautiful views of the West Coast space shuttle.

The photos are a mixture from William G. Hartenstein and the U.S. Air Force. Please check the captions on each page for credit information.

A United Launch Alliance heavy-lift Delta 4 rocket is undergoing final preparations at Vandenberg Air Force Base for the scheduled January 17 flight carrying a large satellite payload for the National Reconnaissance Office. The exact launch time will be announced about five days in advance.

This will be the first West Coast mission for the Delta 4-Heavy booster following four previous launches from Cape Canaveral, Florida.

The California home for Delta 4 is Space Launch Complex 6, the same pad built in the 1980s for the military space shuttle program.

We will have extensive coverage of the upcoming launch.